U.S. patent application number 09/820476 was filed with the patent office on 2001-08-02 for preparation of biopolymer arrays.
Invention is credited to Caren, Michael P., Schembri, Carol T., Schleifer, Arthur.
Application Number | 20010010916 09/820476 |
Document ID | / |
Family ID | 23169686 |
Filed Date | 2001-08-02 |
United States Patent
Application |
20010010916 |
Kind Code |
A1 |
Schleifer, Arthur ; et
al. |
August 2, 2001 |
Preparation of biopolymer arrays
Abstract
A method and apparatus for fabricating an array of biopolymers
on a substrate using a biopolymer or biomonomer fluid, and using a
fluid dispensing head. The head has at least one jet which can
dispense droplets onto a substrate, the jet including a chamber
with an orifice, and including an ejector which, when activated,
causes a droplet to be ejected from the orifice. The method
includes positioning the head with the orifice facing the
substrate. Multiple droplets of the biopolymer or biomonomer fluid
are dispensed from the head orifice so as to form an array of
droplets on the substrate. A gas flow is directed through a venturi
which has a throat opening communicating with the dispensing head
chamber. A venturi control valve which particularly communicate
with an outlet of the venturi, is adjusted to alter the chamber
pressure. The venturi may be driven by a source of inert anhydrous
compressed gas which assists in maintaining fluid in the head
isolated from moisture.
Inventors: |
Schleifer, Arthur; (Portola
Valley, CA) ; Schembri, Carol T.; (San Mateo, CA)
; Caren, Michael P.; (Palo Alto, CA) |
Correspondence
Address: |
AGILENT TECHNOLOGIES, INC.
Legal Department, 51UPD
Intellectual Property Administration
P.O. Box 58043
Santa Clara
CA
95052-8043
US
|
Family ID: |
23169686 |
Appl. No.: |
09/820476 |
Filed: |
March 28, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09820476 |
Mar 28, 2001 |
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09302899 |
Apr 30, 1999 |
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6242266 |
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Current U.S.
Class: |
435/6.11 |
Current CPC
Class: |
B01J 2219/0036 20130101;
B01J 2219/0061 20130101; B01J 2219/00626 20130101; B01J 2219/00722
20130101; B01J 2219/00725 20130101; B01J 2219/00617 20130101; B01J
2219/00637 20130101; B01J 2219/0059 20130101; B01J 2219/00378
20130101; B01J 2219/00612 20130101; B01J 2219/00619 20130101; G01N
35/1074 20130101; B01J 2219/00585 20130101; B01J 2219/00729
20130101; B01J 2219/00527 20130101; B01L 3/0268 20130101; B01J
2219/00605 20130101; B01J 2219/00731 20130101; C40B 40/12 20130101;
C40B 40/14 20130101; C40B 40/06 20130101; B01J 19/0046 20130101;
B01J 2219/00596 20130101; B01J 2219/00689 20130101; C40B 40/10
20130101; C40B 60/14 20130101; B01J 2219/00659 20130101; G01N
2035/1041 20130101 |
Class at
Publication: |
435/6 |
International
Class: |
C12Q 001/68 |
Claims
What is claimed is:
1. A method of fabricating an array of biopolymers on a substrate
using a biopolymer or biomonomer fluid, and using a fluid
dispensing head having: at least one jet which can dispense
droplets onto a substrate, the jet including a chamber with an
orifice, and including an ejector which, when activated, causes a
droplet to be ejected from the orifice; the method comprising: (a)
positioning the head with the orifice facing the substrate; (b)
dispensing multiple droplets of the biopolymer or biomonomer fluid
from the head so as to form an array of droplets on the substrate;
(c) directing a gas flow through a venturi which has a throat
opening communicating with the dispensing head chamber; (d) varying
gas flow resistance on an outlet side of the venturi, to alter the
chamber pressure.
2. A method according to claim 1 wherein gas flow resistance on the
venturi outlet side is adjusted to alter the chamber pressure
before or after step (b).
3. A method according to claim 1 wherein a negative spotting
pressure is provided from the venturi throat opening to the head
chamber during dispensing of the droplets, and wherein the gas flow
resistance of the venturi outlet side is adjusted to provide a
positive chamber pressure.
4. A method according to claim 1 additionally comprising loading
the chamber with fluid from a direction behind the orifice and
wherein, following loading, the gas flow resistance of the venturi
outlet side is increased to provide a positive priming pressure to
the chamber so as to assist in priming the at least one jet.
5. A method according to claim 1 wherein the gas flow resistance of
the venturi outlet side is increased to provide a positive purging
pressure to the chamber so as to purge any fluid remaining in the
chamber through the orifice.
6. A method according to claim 3 additionally comprising adding a
purge fluid to the chamber prior to providing the purging pressure
to the chamber.
7. A method according to claim 1 wherein the gas directed through
the venturi is an anhydrous compressed gas.
8. A method according to claim 1 wherein each fluid droplet has a
volume of from 0.1 to 1000 pL.
9. A method according to claim 1 additionally comprising altering
the gas flow rate through the venturi by adjusting a valve on an
inlet side of the venturi.
10. A method according to claim 1 additionally comprising:
providing a spotting pressure in the chamber from the venturi
throat opening while the head is facing the substrate so as to
retain fluid in the chamber in the absence of the ejector being
activated; and wherein the venturi outlet side gas flow resistance
is increased to provide a purging pressure which is greater than
the spotting pressure and sufficiently positive so as to purge
fluid remaining in the chamber through the orifice.
11. A method according to claim 10 additionally comprising adding a
purge fluid to the head prior to providing the purging pressure to
the head.
12. A method according to claim 1 additionally comprising, prior to
step (a): positioning the head facing a load station spaced from
the substrate, with the orifice adjacent and facing the biomonomer
or biopolymer fluid, and providing a loading pressure in the
chamber from the venturi throat opening while the head is facing
the load station, which is sufficiently negative such that the
fluid is drawn into the chamber through the orifice; and wherein
the gas flow rate through the venturi is adjusted to provide a
spotting pressure while dispensing droplets from the head, which
spotting pressure is higher than the loading pressure.
13. A method according to claim 12 wherein the gas flow rate is
adjusted to provide the spotting pressure by adjusting a valve on
an inlet side of the venturi.
14. A method according to claim 1 additionally comprising:
positioning the head facing a load station with the orifice
adjacent and facing the biomonomer or biopolymer fluid; providing a
loading pressure in the chamber from the venturi throat opening
while the head is facing the load station, which is sufficiently
negative such that the fluid is drawn into the chamber through the
orifice; positioning the head facing a purge station which is
spaced from the substrate; and wherein: the gas flow rate through
the venturi is adjusted by adjusting a valve on an inlet side of
the venturi to provide a spotting pressure while dispensing
droplets from the head, which spotting pressure is higher than the
loading pressure; and following dispensing of droplets, the venturi
outlet side gas flow resistance is increased to provide a purging
pressure in the chamber while the head is facing the purge station
which is sufficiently positive such that fluid in the chamber is
purged through the orifice.
15. A method of fabricating an array of biopolymers on a substrate
using a biopolymer or biomonomer fluid, and using a fluid
dispensing head having: at least one jet which can dispense
droplets onto a substrate, the jet including a chamber with an
orifice, and including an ejector which, when activated, causes a
droplet to be ejected from the orifice; the method comprising: (a)
positioning the head with the orifice facing the substrate; (b)
dispensing multiple droplets of the biopolymer or biomonomer fluid
from the head so as to form an array of droplets on the substrate;
(c) directing a flow of anhydrous gas through a venturi which has a
throat opening communicating with the dispensing head chamber.
16. A method according to claim 15 additionally comprising
providing a spotting pressure in the chamber from the venturi
throat opening while the head is facing the substrate so as to
retain fluid in the chamber in the absence of the ejector being
activated.
17. A method according to claim 15 additionally comprising:
positioning the head facing a purge station which is spaced from
the substrate; and providing a purging pressure in the chamber from
the venturi throat opening so as to purge fluid remaining in the
chamber through the orifice.
18. A method according to claim 15 additionally comprising, prior
to step (a): positioning the head facing a load station which is
spaced from the substrate, with the orifice adjacent and facing the
biomonomer or biopolymer fluid, and providing a loading pressure in
the chamber from the venturi throat opening while the head is
facing the load station, which is sufficiently negative such that
the fluid is drawn into the chamber through the orifice.
19. A method according to claim 15 wherein the head has multiple
pulse jets with orifices on a common front face of the head.
20. A method according to claim 18 wherein fluid is simultaneously
drawn in through the orifice of the multiple jets when the head is
facing the loading station.
21. An apparatus for fabricating an array of biopolymers on a
substrate, comprising: (a) a substrate station on which the
substrate can be mounted; (b) a dispensing head having: at least
one jet which can dispense droplets onto a substrate, the jet
including a chamber with an orifice, and including an ejector
which, when activated, causes a droplet to be ejected from the
orifice; (c) a positioning system to move at least one of the
dispensing head and mounted substrate with respect to the other so
that multiple droplets dispensed from the head onto the substrate
will form an array thereon; (d) a venturi having an inlet and an
outlet, and a throat opening communicating with the chamber; and
(e) an adjustable venturi outlet control valve communicating with
the venturi outlet so that selectable pressure can be applied to
the head chamber by adjustment of the outlet control valve.
22. An apparatus according to claim 21 wherein the venturi outlet
control valve can be adjusted to apply positive or negative
pressure to the dispensing head chamber.
23. An apparatus according to claim 21 additionally comprising a
load station spaced from the substrate station to retain multiple
biopolymer or polymerizable biomonomer reagent solutions for
loading into the head.
24. An apparatus according to claim 21 wherein each fluid droplet
has a volume of from 0.1 to 1000 pL.
25. An apparatus according to claim 21 additionally comprising a
source of anhydrous compressed gas communicating with the venturi
inlet.
26. An apparatus according to claim 21 wherein the venturi outlet
control valve is adjustable to provide selectable different
negative pressures to the chamber.
27. An apparatus according to claim 21 additionally comprising: a
purge station spaced from the substrate station; and a control
processor which operates the positioning system to selectively
position the head facing any one of the stations, and which adjusts
the venturi outlet control valve to a restricted position so as to
provide, when the head is facing the purge station, a positive
pressure to the chamber from the venturi throat opening to purge
fluid from the dispensing head.
28. An apparatus according to claim 21 additionally comprising: a
load station spaced from the substrate station; a control processor
which operates the positioning system to selectively position the
head facing any one of the stations, and which adjusts the venturi
outlet control valve so as to provide, when the head is facing the
load station, a negative pressure to the chamber from the venturi
throat opening to draw fluid positioned adjacent the orifice into
the chamber through the orifice.
29. An apparatus according to claim 21 additionally comprising: a
load station and a purge station which are spaced from the
substrate station; and a control processor which operates the
positioning system to selectively position the dispensing head
facing any one of the stations; and wherein: the control processor
adjusts the venturi outlet control valve to apply negative pressure
to the chamber from the venturi throat opening when the dispensing
head is facing the load station, so as to draw fluid positioned
adjacent the orifice into the chamber through the orifice; and the
control processor adjusts the venturi outlet control valve so that
positive pressure is applied to the chamber from the venturi throat
opening when the dispensing head is facing the purge location, to
force out any fluid in the head.
30. An apparatus according to claim 21 wherein the head has
multiple pulse jets with orifices on a common front face of the
head.
31. An apparatus for fabricating an array of biopolymers on a
substrate, comprising: (a) a substrate station at which the
substrate can be mounted; (b) a dispensing head having: at least
one jet which can dispense droplets onto a substrate, the jet
including a chamber with an orifice, and including an ejector
which, when activated, causes a droplet to be ejected from the
orifice; (c) a positioning system to move at least one of the
dispensing head and mounted substrate with respect to the other so
that multiple droplets dispensed from the head onto the substrate
will form an array thereon; (d) a venturi having an inlet and an
outlet, and a throat opening communicating with the chamber; and
(e) a source of anhydrous compressed gas communicating with the
venturi pressurized gas inlet.
32. An apparatus according to claim 31 additionally comprising a
valve to adjust the gas flow rate through the venturi.
33. An apparatus according to claim 31 wherein the valve is on an
inlet side of the venturi.
34. An apparatus according to claim 31 wherein the head has
multiple pulse jets with orifices on a common front face of the
head.
35. An apparatus for fabricating an array of biopolymers on a
substrate, comprising: (a) a substrate station at which the
substrate can be mounted; (b) a dispensing head having: at least
one jet which can dispense droplets onto a substrate, the jet
including a chamber with an orifice, and including an ejector
which, when activated, causes a droplet to be ejected from the
orifice; (c) an enclosure about the substrate station and
dispensing head so that the head and substrate station can be
maintained in a controlled atmosphere; (d) a positioning system to
move at least one of the dispensing head and mounted substrate with
respect to the other so that multiple droplets dispensed from the
head onto the substrate will form an array thereon; (d) a venturi
having an inlet and an outlet, and a throat opening communicating
with the chamber; and (e) a valve to control gas flow rate through
the venturi.
Description
FIELD OF THE INVENTION
[0001] This invention relates to biopolymer arrays, particularly
polynucleotide arrays such as DNA arrays, which are useful in
diagnostic, screening, gene expression analysis, and other
applications.
BACKGROUND OF THE INVENTION
[0002] Arrays of biopolymers, such as arrays of peptides or
polynucleotides (such as DNA or RNA), are known and are used, for
example, as diagnostic or screening tools. Such arrays include
regions (sometimes referenced as spots) of usually different
sequence biopolymers arranged in a predetermined configuration on a
substrate. The arrays, when exposed to a sample, will exhibit a
pattern of binding which is indicative of the presence and/or
concentration of one or more components of the sample, such as an
antigen in the case of a peptide array or a polynucleotide of
particular sequence in the case of a polynucleotide array. The
binding pattern can be detected, for example, by labeling all
potential targets (for example, DNA) in the sample with a suitable
label (such as a fluorescent compound), and accurately observing
the fluorescence pattern on the array.
[0003] Biopolymer arrays can be fabricated using in situ synthesis
methods or deposition of the previously obtained biopolymers. The
in situ synthesis methods include those described in U.S. Pat. No.
5,449,754 for synthesizing peptide arrays, as well as WO 98/41531
and the references cited therein for synthesizing polynucleotides
(specifically, DNA). Such in situ synthesis methods can be
basically regarded as repeating at each spot the sequence of: (a)
deprotecting any previously deposited monomer so that it can now
link with a subsequently deposited protected monomer; and (b)
depositing a droplet of another protected monomer for linking.
Different monomers may be deposited at different regions on the
substrate during any one iteration so that the different regions of
the completed array will have different desired biopolymer
sequences. One or more intermediate further steps may be required
in each iteration, such as oxidation, capping and washing steps.
The deposition methods basically involve depositing biopolymers at
predetermined locations on a substrate which are suitably activated
such that the biopolymers can link thereto. Biopolymers of
different sequence may be deposited at different regions of the
substrate to yield the completed array. Washing or other additional
steps may also be used. Reagents used in typical in situ synthesis
are water sensitive, and thus the presence of moisture should be
eliminated or at least minimized.
[0004] Typical procedures known in the art for deposition DNA such
as whole oligomers or cDNA, are to load a small volume of DNA in
solution on the tip of a pin or in an open capillary and touch the
pin or capillary to the surface of the substrate. When the fluid
touches the surface, some of the fluid is transferred. The pin or
capillary must be washed prior to picking up the next type of DNA
for spotting onto the array. This process is repeated for many
different sequences and, eventually, the desired array is formed.
Alternatively, the DNA can be loaded into an inkjet head and fired
onto the substrate. Such a technique has been described, for
example, in PCT publications WO 95/25116 and WO 98/41531, and
elsewhere. This method has the advantage of non-contact deposition.
Still other methods include pipetting and positive displacement
pumps such as the Bio-Dot A/D3000 Dispenser available from Bio-Dot
Inc., Irvine, Calif., USA. There are four important design aspects
required to fabricate an array of bioplymers such as cDNA's or DNA
oligomers. First, the array sensitivity is dependent on having
reproducible spots on the substrate. The location of each type of
spot must be known and the spotted area should be uniformly coated
with the DNA. Second, since DNA is expensive to produce, a minimum
amount of the DNA solution should be loaded into any of the
transfer mechanisms. Third, any cross contamination of different
DNA's must be lower than the sensitivity of the final array as used
in a particular assay, to prevent false positive signals.
Therefore, the transfer device must be easily cleaned after each
type of DNA is deposited or the device must be inexpensive enough
to be a disposable. Finally, since the quantity of the assay sample
is often limited, it is advantageous to make the spots small and
closely spaced.
[0005] Similar technologies can be used for in-situ synthesis of
biopolymer arrays, such as DNA oligomer arrays, on a solid
substrate. In this case, each oligomer is formed nucleotide by
nucleotide directly in the desired location on the substrate
surface. This process demands repeatable drop size and accurate
placement on the substrate. It is advantageous to have an easily
cleaned deposition system since some of the reagents have a limited
lifetime and must be purged from the system frequently. Since
reagents, such as those used in conventional phosphoramidite DNA
chemistry may be water sensitive, there is an additional limitation
that these chemical reagents do not come in contact with water or
water vapor. Therefore, the system must isolate the reagents from
any air that may contain water vapor for hours to days during array
fabrication. Additionally, the materials selected to construct
system must be compatible with the chemical reagents thereby
eliminating a lot of organic materials such as rubber.
[0006] Given the above requirements of biopolymer array
fabrication, deposition using an inkjet type head is particularly
favorable. In particular, inkjet deposition has advantages which
include producing very small spot sizes. This allows high-density
arrays to be fabricated. Furthermore, the spot size is uniform and
reproducible as demonstrated by the successful use of inkjets in
printers. Since it is a non-contact technique, ink-jet deposition
will not scratch or damage the surface. Ink-jets have very high
deposition rate, which facilitates rapid manufacture of arrays.
[0007] However, an ink-jet deposition system used for fabricating a
biopolymer array, should meet a number of requirements.
Specifically, the inkjet head must be capable of being loaded with
very small volumes of DNA solution and function with minimal or no
priming of the inkjets. The system should provide for easy purging
of the working solution and readily flushed clean when required.
When used for in-situ synthesis, the system should be able to to
keep reagents isolated from moisture in the surrounding air.
Additionally, use of an inkjet head typically requires that a
negative backpressure (that is, a pressure behind an orifice of the
jet), in the range of one to six inches of water, be supplied to
the inkjet head so that the inkjets form repeatable droplets
without dripping during times when the jet has not been
activated.
[0008] Open-cell foam has been used to provide this negative
backpressure in an inkjet printer in a manner disclosed in U.S.
Pat. No. 4,771,295, such the capillarity of the foam creates the
negative backpressure in an ink reservoir. While this is an easy
and economical way to provide the required negative backpressure,
the foam cannot be easily purged of the working fluid. A small
rubber thimble, similar to an eyedropper, can alternatively be used
but the backpressure will vary as the reservoir is depleted. In
addition, rubber is incompatible with the chemical reagents
typically used in in-situ synthesis. A spring bag reservoir can be
designed to control the backpressure of the fluid reservoir,
however it requires a large working volume and is therefore not a
good choice for the small reservoir volumes required by DNA or
other biopolymer array fabrication. A regulated vacuum source could
also be used. However, this may permit undesirable components, such
as moisture, entering the head particularly during in situ
synthesis. Additionally, purging the inkjet head then requires
extra valves and a compressed nitrogen (or other suitable gas)
source. Gravity is one of the easiest backpressure control means,
however the backpressure changes as the fluid height drops and it
requires too large a fluid volume to work properly for the small
volumes encountered in an inkjet. It would be desirable then, to
provide an apparatus and method for fabricating arrays of
biopolymers which can use an inkjet type head or other pulse jet
head, and which provides for easy purging and cleaning of the head.
It would further be desirable that such an apparatus and method
provide a simple way of providing a controlled negative
backpressure to the head and also provide a simple way of purging
the head, without an overly complex system of valves. It would also
be desirable that any apparatus and method facilitates isolating
reagents in the head from moisture or other undesirable components,
and that it is of a compact construction given the small size of
other components typically encountered in polynucleotide
synthesis.
SUMMARY OF THE INVENTION
[0009] The present invention then, provides a method of fabricating
an array of different or the same moieties (for example, multiple
different chemical compounds) on a substrate using one or more
suitable fluids, and using a fluid dispensing head. The invention
is particularly useful for the in situ process since it provides
the required head pressure while facilitating isolation of reagents
from moisture or other undesirable components. However, the
invention is also applicable to the direct deposition of
polynucleotides. Particularly, the invention provides a method of
fabricating an array of biopolymers using a biopolymer containing
fluid, or one or more fluids containing a biomonomer. The head has
at least one jet which can dispense droplets of a fluid onto a
substrate, the jet including a chamber with an orifice, and
including an ejector which, when activated, causes a droplet to be
ejected from the orifice. The head may particularly be of a type
commonly used in inkjet printers, in which a plurality of pulse
jets (such as those with thermal or piezoelectric ejectors) are
used, with their orifices on a common front surface of the
head.
[0010] The method comprises positioning the head with the orifice
facing the substrate. Multiple fluid droplets of the biopolymer,
biomonomer or other fluid, are dispensed from the head orifice so
as to form an array of droplets on the substrate (this formed array
may or may not be the same as the final desired array since, for
example, multiple heads can be used to form the final array). A gas
flow is directed through a venturi which has a throat opening
communicating with the dispensing head chamber. The gas used may be
any suitable gas which may be selected depending upon the reagent
chemistry. For example, when phosphoramidite oligonucleotide
synthesis or other water sensitive chemistries are used, the gas
should preferably be an inert anhydrous compressed gas such as
anhydrous nitrogen. By "inert" in this context is referenced no
substantial adverse reaction with a reagent. Gas flow rate through
the venturi may be adjusted to alter the chamber pressure. This
adjustment can occur whenever it is desired to change the pressure
in the chamber, for example before or after the dispensing step.
The adjustment can be accomplished by suitable means such as a
valve on the venturi inlet and/or outlet side, or some other way of
at least partially obstructing the inlet and/or outlet side (for
example, an operator may simply manually block the outlet side). It
will be appreciated from this arrangement, that all of the
pressures in or at various chambers in the head therefore, are
typically gas pressure (that is, provided by a gas in the location
specified).
[0011] The venturi throat opening may provide a negative spotting
pressure to the head chamber during dispensing of the droplets, and
the gas flow resistance of the venturi outlet side may be adjusted
(before or after dispensing) to provide a positive chamber
pressure. This positive pressure may be provided by increasing the
gas flow resistance of the venturi outlet side before dispensing
(for example, as a priming pressure so as to assist in priming the
jets) or after dispensing (for example, as a purging pressure so as
to assist in purging any fluid remaining in the chamber out through
the orifice). The priming and purging pressures may be the same or
different, and each will typically be higher than the spotting
pressure. In the case of purging, a purge fluid may optionally be
added to the head chamber prior to providing the purging
pressure.
[0012] In one aspect of the method, which is particularly useful
for (but not limited to) the in situ method, the chamber is loaded
with the fluid from a direction behind the orifice (that is, liquid
is not loaded through the orifice). Following loading, the gas flow
resistance of the venturi outlet side is increased to provide a
positive priming pressure to the chamber. This assists in forcing
liquid into the one or more jets to prime them.
[0013] In another aspect, which is particularly useful for (but not
limited to) the deposition of previously obtained biopolymers, the
method may additionally include, prior to the dispensing step,
loading the head with a fluid, such as a fluid containing a
biomonomer (for example, a nucleotide reagent), biopolymer (for
example, a pre-synthesized oligonucleotide, cDNA, or DNA purified
or amplified from a natural source), or other fluid (for example a
fluid containing a moiety or a reagent used in producing such
chemical a moiety). This loading step includes positioning the head
facing a load station which is spaced from the substrate, with the
one or more orifices adjacent and facing the fluid to be loaded. A
loading pressure is provided in the chamber from the venturi throat
opening while the head is facing the load station, which is
sufficiently negative such that the fluid is drawn into the chamber
through the one or more orifices. The gas flow rate through the
venturi is adjusted to provide a spotting pressure to the chamber
while dispensing droplets from the head, which spotting pressure
may be the same or higher (that is, less negative) than the loading
pressure. This adjustment may, for example, be accomplished by
adjusting a valve on the inlet side of the venturi.
[0014] The method may include the loading, spotting and purging
steps as described above.
[0015] In another aspect, the present invention provides a method
of fabricating an array of different moieties, particularly
biopolymers on a substrate using a biopolymer or biomonomer fluid,
and using a fluid dispensing head as described above, which method
includes positioning the head with the orifice facing the
substrate. Multiple fluid droplets of the biopolymer, biomonomer,
or other fluid are dispensed from the head so as to form an array
of droplets on the substrate. A flow of inert anhydrous gas is
directed through a venturi which has a throat opening communicating
with the dispensing head chamber. This aspect may additionally
include providing any of the loading, spotting and purging
pressures, in the same manners as mentioned above. The head used in
the method may have multiple pulse jets with orifices on a common
front face of the head, such as a typical inkjet printing head. In
this case, some or all of the jets can be loaded with the same or
different fluids (biopolymer or otherwise, for example,
deprotection reagent or other reagent).
[0016] An apparatus which can be used to execute a method of the
present invention is also provided. In one aspect, the apparatus
comprises a substrate station on which the substrate can be
mounted, and a fluid dispensing head, and venturi, all as described
above. The apparatus may further include a source of inert
anhydrous gas communicating with the venturi pressurized inlet,
and/or a valve to adjust the gas flow rate through the venturi (the
valve being on the inlet or outlet side of the venturi, or a valve
can be provided on both sides). A positioning system moves at least
one of the dispensing head and mounted substrate with respect to
the other, so that multiple droplets dispensed from the head onto
the substrate will form an array thereon. The apparatus may further
include, particularly in the aspect used for deposition of
previously obtained biopolymers, the load and purge stations. A
control processor may be present to operate the positioning system
to selectively position the head facing any one of the stations,
and which processor also adjusts the venturi outlet control valve
to any of the required positions. In a particular embodiment, the
load station comprises a plate on which multiple drops of different
solutions can be retained.
[0017] The method and apparatus of the present invention can
provide a simple way of controlling backpressure in a pulse type
fluid dispensing head, and can also provide a simple way of purging
the head, without requiring an overly complex system of valves. The
apparatus and method can also facilitate isolating reagents in the
head from moisture or other undesirable components.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a perspective view of a substrate bearing multiple
arrays, as may be produced by a method and apparatus of the present
invention;
[0019] FIG. 2 is an enlarged view of a portion of FIG. 1 showing
some of the identifiable individual regions of a single array of
FIG. 1;
[0020] FIG. 3 is an enlarged cross-section of a portion of FIG.
2;
[0021] FIG. 4 is a schematic view showing components of an
apparatus of the present invention;
[0022] FIG. 5 is a schematic view of an apparatus of the present
invention utilizing the components of FIG. 4;
[0023] FIG. 6 is another embodiment of an apparatus of the present
invention;
[0024] FIG. 7 is an enlarged cross-section of a load station of the
apparatus of FIG. 1;
[0025] FIG. 8 is an enlarged cross-section of a purge station of
the apparatus of FIG. 1;
[0026] FIG. 9 is an enlarged cross-section of a cleaning station of
the apparatus of FIG. 1;
[0027] FIG. 10 is a top view of a fluid dispensing head used in an
apparatus of the present invention;
[0028] FIG. 11 is a bottom view of the head of FIG. 7; and
[0029] FIG. 12 is a cross-section along the line 9-9 in FIG. 7.
[0030] To facilitate understanding, identical reference numerals
have been used, where practical, to designate corresponding
elements that are common to the Figures. Figure components are not
drawn to scale.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0031] In the present application, unless a contrary intention
appears, the following terms refer to the indicated
characteristics. A "biopolymer" includes peptides or
polynucleotides, as well as such compounds composed of or
containing amino acid or nucleotide analogs or non-nucleotide
groups. This includes those compounds in which the conventional
polynucleotide backbone has been replaced with a non-naturally
occurring or synthetic backbone, and those a nucleic acid in which
one or more of the conventional bases has been replaced with a
synthetic base capable of participating in Watson-Crick type
hydrogen bonding interactions. Polynucleotides include single or
multiple stranded configurations, where one or more of the strands
may or may not be completely aligned with another. A "nucleotide"
refers to a subunit of a nucleic acid and includes a phosphate
group, a 5 carbon sugar and a nitrogen containing base, as well as
analogs of such subunits. Specifically, a "biopolymer" includes DNA
(including cDNA), RNA and oligonucleotides. An "oligonucleotide"
generally refers to a nucleotide multimer of about 10 to 100
nucleotides in length, while a "polynucleotide" includes a
nucleotide multimer having any number of nucleotides. A
"biomonomer" references a single unit, which can be linked with the
same or other biomonomers to form a biopolymer (for example, a
single amino acid or nucleotide with two linking groups one or both
of which may have removable protecting groups). A biomonomer fluid
or biopolymer fluid reference a fluid containing either a
biomonomer or biopolymer, respectively. An "array", unless a
contrary intention appears, includes any one or two dimensional
arrangement of discrete regions bearing particular moieties (for
example, different polynucleotide sequences) associated with that
region. It will also be appreciated that throughout the present
application, words such as "upper", "lower" and the like are used
with reference to a particular orientation of the apparatus with
respect to gravity, but it will be understood that other operating
orientations of the apparatus or any of its components, with
respect to gravity, are possible. Reference to a "droplet" being
dispensed from a pulse jet herein, merely refers to a discrete
small quantity of fluid (usually less than about 1000 pL) being
dispensed upon a single pulse of the pulse jet (corresponding to a
single activation of an ejector) and does not require any
particular shape of this discrete quantity. "Fluid" is used herein
to reference a liquid. Further, when reference is made in this
application to providing a pressure within the dispensing head or a
chamber therein this refers, unless a contrary indication appears,
to a pressure therein relative to the pressure immediately outside
the head pulse jet orifices. Such pressures can be provided by
varying the pressure outside the head, or inside the head, or
both.
[0032] Referring first to FIG. 1, either embodiment of invention
described below may produce multiple identical arrays 12 (only some
of which are shown in FIG. 1) across the complete surface of a
single substrate 14. However, the arrays 12 produced on a given
substrate need not be identical and some or all could be different.
Each array 12 will contain multiple spots or regions, 16. As
mentioned above, an array 12 may contain any number of multiple
regions, with a typical number being from 100 to 10,000 regions
(although more or less are possible). All of the regions 16 may be
different, or some or all could be the same. All of the regions 16
may be different, or some or all could be the same. Each region
carries a predetermined moiety or a predetermined mixture of
moieties, such as a particular polynucleotide sequence or a
predetermined mixture of polynucleotides. This is illustrated
somewhat schematically in FIG. 3 where regions 16 are shown as
carrying different polynucleotide sequences.
[0033] Referring to FIG. 4 the illustrated apparatus includes a
fluid dispensing head 209 which is positioned on a reagent
reservoir 207. Head 209 is an inkjet type of printing head with
multiple jets each having an orifice, a dispensing chamber and an
ejector which, when activated, causes a droplet to be ejected from
the orifice. Head 209 may be of similar construction to head 210
described below in connection with FIGS. 6 and 10-12. However,
cover 219 and the individual reservoir chambers 222 of head 210 may
be omitted. Each reservoir 207 may have a capacity of only about 1
or 2 ml. A septum 205 allows sealed access to the interior chamber
defined by reservoir 207 by means of a syringe. Septum 205 may be
made of rubber or other suitable resilient material in a known
manner. A venturi 80 has inlet and outlet sides 82, 90,
respectively, an outlet opening 91, and a throat opening which
communicates with reservoir 207 and hence communicates with the
dispensing chambers of head 209. A flow of an anhydrous inert gas
(particularly nitrogen) can be directed through venturi 80 from an
adjustable flow regulator 85 (which may be regarded as a type of
valve) and compressed nitrogen tank 88.
[0034] An apparatus using the components of FIG. 4 is schematically
illustrated in FIG. 5. This apparatus is particularly useful for an
in situ method of forming polynucleotides on a substrate 10 using a
procedure such as mentioned above. Four sets of the components
shown in FIG. 4 are used in the apparatus of FIG. 5, with the
exception that only a single compressed nitrogen tank 88 is used to
supply all four adjustable flow regulators 85. A substrate station
20 can receive and retain substrate 10 thereon. A flood station 68
is provided to expose an entire substrate with reagents which are
used in the in situ process to simultaneously treat all regions 16
during their formation (for example, with deprotection and washing
solutions). Substrate station 20 is mounted for movement on a
carriage 62 in both an "X" and "Y" direction using a suitable
transporter (not shown). An enclosure 120 is positioned about the
dispensing heads 209 and arranged to allow substrate station 20 to
move in and out of it. Enclosure 120 permits the head and substrate
station to be maintained in a controlled atmosphere environment
(such as an anhydrous nitrogen atmosphere provided from a suitable
external source). Movement of substrate station 20 and operation of
heads 209 and flood station 68, can all be coordinated by a
suitable processor in an analogous manner to that described in
connection with the embodiment FIG. 6.
[0035] In operation of the apparatus of FIG. 5, flow regulators 85
can be manually adjusted to direct an anhydrous nitrogen flow
through each venturi 80 from the inlet side 82 to the outlet side
90. The flow rate is sufficient to provide the spotting pressure to
each of the four reservoirs 207. Suitable spotting pressures (which
will be slightly negative) are mentioned below. In the event that
any water vapor may be present in reservoirs 207, they can
initially be flushed with anhydrous nitrogen by increasing gas flow
resistance on the outlet side 90 of each venturi. This can be
accomplished such as by briefly manually blocking each outlet
opening 91 (an operator can readily use their finger for this
purpose since each venturi 80 may only be in the order of less than
10 mm in width or length). Alternatively, a valve (such as valve 94
described in connection with FIG. 6) communicating with outlet side
90, could be used rather than manual blocking. This causes a
nitrogen flow from regulators 85 to be briefly forced through lines
96 and hence into reservoirs 207 and out the orifices of the heads
209. Following flushing, the pressure within reservoirs 207 returns
to the spotting pressure. Each of reservoirs 207 may then be loaded
with respective nucleotide reagents through its septum 205 using a
syringe. Given the capillary size of the dispensing chambers and
orifices of heads 209, all jets may not be properly primed such
that activation of any ejector may not yield a droplet of the
expected volume. To ensure proper priming, a priming pressure
(which is a positive pressure) can be applied to reservoirs 207.
This can be accomplished by again increasing gas flow resistance on
the outlet side 90 of venturis 80, in a manner already described.
Enclosure 120 is provided with a nitrogen atmosphere and carriage
62 positions substrate 10 within enclosure 120 facing the orifices
of heads 209. The processor then controls movement of substrate 10
in the X and Y directions while coordinating activation of the
ejectors in heads 209, such that droplets are dispensed from heads
209 so as to form an initial array or pattern of droplets on
substrate 10. A single array or multiple arrays of droplets can be
dispensed in this manner with intervening movement of substrate 10
by carriage 62 to flood station 68 for treatment of all deposited
spots with reagents, as required. The final product is one or more
biopolymer arrays on substrate 10.
[0036] Typically, there is sufficient capacity within reservoirs
207 such that many substrates 10 can be treated in turn by the
above method to form many arrays. At some point though, it becomes
necessary to flush reservoirs 207 and heads 209. Gas flow
resistance on the outlet side 90 of each venturi can then be
increased in a manner already described. As already mentioned, this
will cause nitrogen to flow through lines 96 and increase pressure
within reservoirs 207 to what is referenced as a "purging
pressure", so as to force any liquid within reservoirs 207 out
through the orifices in heads 209. This purging pressure is, in
practice, a positive pressure which may be about the same as the
priming pressure. Openings 91 can be uncovered when all liquid
appears to have been purged from reservoirs 207. A syringe can then
be used to add a purge fluid (such as a solvent) to each reservoir
207 through septa 205, and the foregoing purging procedure
repeated.
[0037] Referring now to the embodiment of FIG. 6 the apparatus
includes a substrate station 20 on which can be mounted the
substrate 14. Substrate station 20 can include a vacuum chuck
connected to a suitable vacuum source (not shown) to retain a
mounted substrate 14 without exerting too much pressure thereon,
since substrate 14 is often made of glass. A load station 30, purge
station 40, and cleaning station 50 are spaced apart from one
another an substrate station 20. Load station 30 can be of any
construction with regions which can retain small volumes of
different fluids for loading into head 210. For example, it may be
a glass surface with different hydrophobic and hydrophilic regions
to retain different drops thereon in the hydrophilic regions.
Alternatively, the flexible microtitre plate described in U.S.
patent application "Method and Apparatus for Liquid Transfer", Ser.
No. 09/183,604 could be used. In the drawings load station 30 and
has an upper surface with small notches 32 to assist in retaining
multiple individual drops of a biomonomer or biopolymer fluid on
that surface. The number of notches 32 or other regions for
retaining drops of different fluids, is at least equal to (and can
be greater than) the number of reservoir chambers 222 in a printer
head 210 (described further below), and are spaced to align with
orifices 214 in head 210. Even where the number of such fluid
retaining regions is less than the number of orifices 214, all
delivery chambers communicating with one another (through a
reservoir chamber 222) can still be filled in the present
invention. This occurs since, with the previously defined load
pressure value, fluid which has entered a reservoir chamber 222
through one orifice 214 can still be drawn by capillary pressure
into other delivery chambers communicating with the same reservoir
chamber 222.
[0038] Purge station 40 has an upper surface defined by a generally
rectangular urethane gasket 43 and a region 42 interior of gasket
43. Interior region 42 communicates with a vacuum line 72. A vacuum
source 74 communicates through vacuum line 72 and an electrically
controlled valve 70, which is controlled by a processor 140 through
control line 76. Vacuum source may include a suitable vacuum supply
(such as a pump) as well as a trap. Gasket 43 is dimensioned such
that a periphery of a front face of a dispensing head 210
(described in more detail below) can sealingly engage against upper
surface 43 with interior region 42 aligned and communicating with
the two rows of orifices 214 in head 210. In this manner, orifices
214 can be placed in communication with vacuum line 72 so that,
during a purging step (described further below) vacuum from line 72
can pull fluid out of head 210 through orifices 214. Any processor
in the present application, including processor 140, may be a
general purpose microprocessor suitably programmed to execute all
of the steps required by the present invention, or any hardware or
software combination which will perform the required functions.
[0039] Cleaning station 50 can retain an upwardly facing pad 52
which can be saturated with a suitable cleaning fluid. A dispensing
head 210 (described in more detail below) is retained by a head
retainer 208. Head 210 can be positioned to face any one of loading
station 30, substrate station 20, purge station 40, or cleaning
station 50 by a positioning system. The positioning system includes
a carriage 62 connected to each of the foregoing stations, a
transporter 60 controlled by processor 140 through line 66, and a
second transporter 100 controlled by processor 140 through line
106. Transporter 60 and carriage 62 are used execute one axis
positioning of any of the stations 20, 30, 40 and 50 facing the
dispensing head 210 by moving them in the direction of arrow 63,
while transporter 100 is used to provide two axis adjustment of the
position of head 210 in a vertical direction 202 or in the
direction 204. Further, once substrate station 20 has been
positioned facing head 210, transporter 100 will be used to scan
head 208 across a mounted substrate 10, line by line. However, it
will be appreciated that both transporters 60 and 100, or either
one of them, with suitable construction, can be used to perform any
necessary positioning (including the foregoing scanning) of head
210 with respect to any of the stations. Thus, when the present
application recites "positioning" one element (such as head 210) in
relation to another element (such as one of the stations 20, 30, 40
or 50) it will be understood that any required moving can be
accomplished by moving either element or a combination of both of
them.
[0040] Head retainer 208, and hence head 210 (specifically,
delivery chambers 217 of head 210 as described below), communicates
with a source of purging fluid, such as tank 110, through line 112
in which is provided an electrically operable valve 114 controlled
by processor 140 through control line 116. The apparatus further
includes a venturi 80 having an inlet side 82 communicating through
line 84 and an adjustable flow regulator 86, with a source of
compressed anhydrous inert gas in the form of nitrogen tank 88.
Flow regulator may optionally be adjusted under control of
processor 140 through line 87. Since a flow regulator may be
regarded as a type of valve, flow regulator 86 will often be
referenced herein as valve 86. An adjustable venturi outlet control
valve 94 communicates with a venturi outlet 90 through line 92.
Valve 94 is electrically operable by processor 140 through line 98
and may be of any suitable type, such a simple pivoting gate valve.
A throat opening 89 in venturi 80 communicates with head retainer
208, and hence head 210, through line 96. It will be appreciated
that with the foregoing arrangement, selectable negative or
positive pressure can be applied to head 210 from throat opening 89
by adjustment of valve 94 only. Optionally, selectable negative
pressures can also be applied by adjustment of valve 86. Thus, in
the discussion below where negative pressures are varied by
adjusting valve 94, it will be understood that this can instead (or
additionally) be accomplished by adjusting valve 86, and that
corresponding settings of valve 86 (or both valves) for providing
the recited negative pressures can be substituted for the negative
pressure producing settings of valve 94. Furthermore, it will be
appreciated that when valve 94 is at least partially closed to
provide a positive pressure in head 210 from throat opening 89,
such pressure will be provided by the anhydrous nitrogen from
cylinder 88 thereby avoiding contact of fluid in head 210 with
moisture or other contaminants. However, if the fluids in head are
not sensitive to moisture or other particular gasses, a source of
compressed gas other than the anhydrous nitrogen source can be
used. When the fluids are moisture or otherwise sensitive,
dispensing station 20 and head 208, and such other components as
may be required or desired, can be enclosed in a controlled
atmosphere environment (such as a nitrogen fed environment).
[0041] Referring now to Figures FIGS. 10, 11, these show in plan
view a particular fluid dispensing head 210 of the apparatus of
FIG. 6. Head 210 has multiple fluid dispensing jets, and six
reservoir chambers 222 and three hundred capillary delivery
chambers 217. In a front view, FIG. 10, an orifice member 212 (here
an orifice plate) represents a front face of head 210, and has
orifices 214 disposed in two orifice rows 213, 215. Each orifice
214 can be regarded as part of a delivery chamber 217, and tapers
inwardly away from a delivery chamber 217 toward an open end 214a
of the orifice 214. Prototypes having this configuration were
constructed having 150 orifices in each of the orifice rows. Thus,
while each fluid pulse jet includes a fluid dispensing chamber 217,
an ejector 224 as described below, and a reservoir chamber 222, the
six reservoir chambers 222 are shared among a number of delivery
chambers 217 (that is, each reservoir chamber 222 has multiple
delivery chambers 217), while each pulse jet, of course, has its
own ejector 224. It will be appreciated that the number of orifices
and corresponding ejectors could of course be varied, for example
between 10 to 300 or to 500 or more, depending upon their size and
materials used to construct head 210. Rearward of orifice member
212 are barrier 220 and adhesive 221, and, resting upon adhesive
221 is reservoir block 218 and resting upon barrier 220 is back
member 216 (here a silicon die, as described more fully below), all
more readily understood with reference to a rear view as in FIG. 11
and to a sectional view as in FIG. 12.
[0042] In a particular configuration, the barrier 220 is a photo
polymer layer, and accordingly the delivery chambers (for example
delivery chambers 217) are defined in part by the inner surface 211
of the orifice plate 212, in part by the front surface of the
margin (for example surface 226) of the back member 216, and in
part by an edge (for example edge 225) of the portion of the photo
polymer layer 220 situated between the orifice plate and the back
member. And, in such a configuration, the reservoirs (for example
reservoir 222), which are not separate from the delivery chambers,
are defined in part by a portion of an edge of the back member (for
example edge portion 227), and in part by an inner wall (for
example wall 228) of the reservoir block 218 together with an edge
(for example edge 229) of the adhesive layer, situated partly
between the reservoir block 218 and the orifice plate 212.
[0043] A cover 219 (removed in FIG. 11; shown in sectional view in
FIG. 12) is affixed to the rear surface of the reservoir block 218,
and sealed peripherally (for example by means of an "O" ring 223)
so that it provides a common enclosure for the reservoirs. Cover
219 is provided with a port 221, permits communication with holder
208 and hence lines 112 and 97. As will be appreciated, the
delivery chambers and reservoirs of the device of FIGS. 10-12 can
be filled with fluid by contacting the exit ends of the orifices
with a quantity of the fluid and then lowering the pressure
upstream from the orifices by connecting a source of vacuum at the
port in the cover, resulting in drawing fluid in an upstream
direction through the orifices into the delivery chambers and then
into the reservoirs. Selected different fluids (or fluids
containing different materials) can be drawn into the different
chambers and reservoirs by contacting each orifice group (in fluid
communication with a delivery chamber) with a different fluid.
[0044] Opposite each orifice 214 on the front surface 226 of the
margin of the back member is an ejector 224 (here an electrical
resistor operating as a heating element), which is electrically
connected to a source of electrical energy which can be controlled
to deliver a suitable pulse of electricity to activate the ejector
on demand. (The connectors, the source of electrical energy, and
the controller are not shown in the Figs.). In a particular
embodiment the back member is a silicon die, and the electrical
parts (heating element and connectors, for example) are formed
using conventional solid state silicon ship manufacturing
techniques.
[0045] The various fluid-handling parts of the head 210 generally
have the following characteristics. The size of each orifice in the
orifice plate is one that produces a spot of suitable dimensions on
the substrate surface, where the orifice generally has an exit
diameter (or exit diagonal depending upon the particular format of
the device) in the range about 1 .mu.m to 1 mm, usually about 5
.mu.m to 100 .mu.m, and more usually about 10 .mu.m to 60 .mu.m.
The fluid capacity of the delivery chamber is in the range about 1
pL to 10 nL, usually about 10 pL to 5 nL and more usually about 50
pL to 1.5 nL. The reservoir chamber 222 and the connected delivery
chamber 217, with which any one of the orifices 214 communicate,
together have a combined fluid capacity in the range about 1 pL up
to 1 mL (more typically less than 100 .mu.L), usually about 0.5
.mu.L to 10 .mu.L, and more usually about 1 .mu.L to 5 .mu.L. The
front-to-rear thickness of the delivery chamber, defined by the
space between the rear surface of the orifice plate and the front
surface of the margin of the back plate, may in some embodiments be
in the range less than about 100 .mu.m, for example in prototypes
of embodiments shown in the Figures herein, in the range 10 .mu.m
to 60 .mu.m.
[0046] Where the ejector is a heating element, the heating element
will preferably be made out of a material that can deliver a quick
energy pulse, and suitable materials include TaAl and the like. The
thermal element is capable of achieving temperatures sufficient to
vaporize a sufficient volume of the fluid in the firing chamber to
produce a bubble of suitable dimensions upon actuation of the
ejector. Generally, the heating element is capable of attaining
temperatures at least about 100.degree. C., usually at least about
400.degree. C., and more usually at least about 700.degree. C., and
the temperature achievable by the heating element may be as high as
1000.degree. C. or higher. It will be appreciated of course, that
other ejector types, such as piezoelectric ejectors, could be used
instead of a heating element.
[0047] A device as in FIGS. 10-12 can be constructed by adaptation
of techniques known in the printing art and, particularly, in the
art of inkjet device construction. Certain elements of the device
of FIGS. 10-12 can be adapted from parts of a commercially
available thermal inkjet print head device available from
Hewlett-Packard Co. as part no. HP51645A. Various other dispensing
head designs can be used, such as those described in U.S. patent
application entitled "A MULTIPLE RESERVOIR INK JET DEVICE FOR THE
FABRICATION OF BIOMOLECULAR ARRAYS" Ser. No. 09/150,507 filed Sep.
9, 1998. That reference and all other references cited in the
present application are incorporated herein by reference.
[0048] It should be noted that the above dimensions of the head
210, and particularly the dimensions of the deliver chamber 217
(and included orifices 214) are small enough that capillary forces
can have a significant effect on the fluid pressures within the
fluid column contained within these and larger fluid-handling
parts. Particularly, each orifice 214 and connected capillary
delivery chamber 217 are so dimensioned that they can be expected
to fill by capillary action when the orifice 214 is brought into
contact with the meniscus of a liquid to be loaded into the pulse
jet. Reservoir chamber 222 is also capillary but it may be
non-capillary (by non-capillary is meant that it is so dimensioned
that it will not fill by capillary action after delivery chamber
217 has completely filled). While reservoir chamber 222 is
capillary it is distinguishable from the delivery chamber 217.
However, reservoir chamber 222 could be dimensioned such that it is
indistinguishable from delivery chamber 217 (in which case the
reservoir and delivery chambers may be the same chamber). A
slightly negative loading pressure can simultaneously be applied to
chamber 222 from pressure source 80 during a load step (described
further below), which is sufficiently negative such that the fluid
is drawn into the reservoir chamber 222 through the delivery
chamber 217 while simultaneously being insufficient to result in
ambient atmosphere entering the delivery when no further fluid is
facing and adjacent the orifice (typically when a drop of liquid to
be loaded, has been completely loaded). Otherwise, fluid being
loaded into a jet through an orifice would be drawn into delivery
chambers 217 with possible loss of prime of the jets. That is, the
delivery chambers 217 should be completely filled (and preferably
along with at least part of reservoir chambers 222), with a liquid
face or meniscus being maintained within orifice 214 and preferably
at the open end 214a of the orifices 214. Air entering orifices 214
after loading may result in loss of this condition.
[0049] Venturi 80, in the presence of a sufficient flow of
anhydrous nitrogen from tank 88 and valve 86, is also capable of
providing a "spotting pressure" which is slightly negative, but is
typically higher (that is, less negative) than the loading
pressure, during a dispensing step (described below). The spotting
pressure is sufficient to retain fluid within the jets in the
absence of activation of a given ejector 224. This can be obtained
by processor 140 at least partially closing valve 94 from the load
setting to a more restricted spotting position. The spotting
pressure will typically be a known quantity for a given head 210 or
can also be readily determined by experimentation. Additionally,
valve 94 can be further closed from the spotting setting to a
"cleaning setting" such that throat opening 89 provides in
reservoir chamber 222 a holdoff pressure which is sufficiently
positive to prevent liquid contacting the orifices 214 during a
head cleaning step (described below) from entering delivery
chambers 217 through the orifices 214. The holdoff pressure is a
gas pressure in the reservoir chamber 217 (that is, there is a gas
in the delivery chamber). It will also be appreciated that during a
purge step for head 210 (described below), a positive "purging
pressure" which is provided to reservoir chamber 222 by providing a
negative pressure from pump 74 to purge station 40, could instead
be replaced by providing a positive pressure to reservoir chamber
22 from throat opening 89 by at least partially closing valve 94.
In this case the corresponding "purge setting" of valve 94 will
typically be a further closed position from the cleaning setting
since the purging pressure will typically be higher than the
holdoff pressure.
[0050] The loading pressure is a negative pressure which will
typically be less than the capillary pressure within a given jet
during loading (for example, 10-90% of the capillary pressure),
although allowances may need to be made for other factors such as
the weight of the fluid column in a jet during loading (although in
most fluid heads this will be negligible compared to capillary
pressure). The mensiscus at an orifice 214 has a capillary pressure
based on its curvature. To avoid air (or other ambient gas) from
entering a delivery chamber 217 the meniscus should not move away
from the end of an orifice 214. This basically implies that the
value of the loading pressure should be below this capillary
pressure. A suitable loading pressure for any particular apparatus
can be readily determined by experimentation, simply by adjusting
valve 94 (and/or valve 86 as already mentioned) until the required
result is observed. That is, liquid to be loaded is drawn into
reservoir chamber 222 without ambient atmosphere outside orifices
214 entering the delivery chamber 217 after the reservoir chambers
have been loaded and there is no further fluid facing and adjacent
the orifices 214. When too high a negative pressure is used, entry
of ambient atmosphere into delivery chambers 217 can be observed
directly or from the fact that the jets have lost their prime. When
prime is lost, one way to regain it is to purge the head and reload
it. The load setting of valve 94 can be recorded by processor 140
or can be set mechanically in valve 94. Suitable spotting, purge
and holdoff pressures can also be readily determined by
experimentation or calculation, and the corresponding settings of
valves 84, 94 recorded by processor 140. Generally, the purging
pressure is greater than the holdoff pressure which is greater than
the spotting pressure, which is in turn greater than the loading
pressure (that is, the spotting pressure is less negative than the
loading pressure). For example, ambient pressure will typically be
about 14.7 psia, the capillary pressure in a head of the above
described type might be about 18 inches of water (0.65 psig), while
the loading pressure might typically be about 8 inches of water
below atmosphere (that is, below ambient pressure). The holdoff
pressure is greater than the capillary pressure, typically about 2
to 3 times the capillary pressure (for example, about 2 psig or 55
inches of water above atmosphere), while the spotting pressure is
typically about 10-90% of the capillary pressure (for example,
about 5 inches of water, or 0.18 psig, below atmosphere). The
purging pressure will typically be many times the capillary
pressure, for example about 10 to 12 psig or 275-330 inches of
water above atmosphere. Description of the pressure adjustments is
also provided in U.S. Patent Application entitled"FABRICATING
BIOPOLYMER ARRAYS", by M. Caren et al., assigned to the same
assignee as this application, Attorney Docket No. 10990640, filed
on the same date as the present application.
[0051] The apparatus of FIGS. 4 through 5 can fabricate arrays of
different moieties, including arrays of different biopolymers, such
as those illustrated in FIGS. 1 to 3. Operation of the apparatus to
generate biopolymers will now be described although it will be
understood that analogous methods can be used to generate arrays of
other moieties. First, it will be assumed that tank 110 contains a
suitable purging fluid (usually a buffered solution), that valve 86
has been manually opened to provide a flow of anhydrous nitrogen so
that adjustment of valve 94 (and/or valve 86, as already mentioned)
to the load, spotting, and cleaning settings (and optionally a
purge setting) will cause the throat opening to provide the load,
spotting and holdoff pressures (and optionally a purging pressure).
It will also be assumed that drops of different biomonomer or
biopolymer containing fluids (or other fluids) have been placed at
respective notches 32 (or other drop retaining regions) of load
station 30. This placement can be accomplished by manual or
automated pipetting, or spotting of drops onto load station 30
using glass rods, which are of a volume required to load all of the
pulse jets. Alternatively, as already mentioned, the flexible
microtitre plate described in U.S. patent application "Method and
Apparatus for Liquid Transfer", Ser. No. 09/183,604 could be used
as load station 30. Also, pad 52 has been previously placed in
cleaning station 50 and saturated with a suitable cleaning
solution. Operation of the following sequences are controlled by
processor 140 unless a contrary indication appears.
[0052] A loading sequence is initiated in which processor 140
directs the positioning system to position head 210 facing load
station 30 with the orifices aligned, facing, and adjacent to
respective drops on load station 30. As previously mentioned,
during any positioning operation one axis positioning of the head
210 facing the required station can be accomplished through
transporter 60, and then the other two axes positioning of head 210
can be accomplished through transporter 100. Processor 140 may
optionally ensure valve 86 is open and selects the load setting of
valve 94 so that the loading pressure is applied to load chamber
222 and hence to delivery chamber 217. Capillary pressure will
cause fluid to then simultaneously flow in through orifices 214 to
fill delivery chambers 217 and reservoir chambers 222. The load
pressure assists in this filling by causing the fluid to flow
faster. At this point, or shortly thereafter, there will be no
further fluid facing and adjacent orifices 214, either because the
fluid at load station 30 is exhausted or head 210 is moved away
from load station 30. In the case where head 210 is moved away
before all fluid is exhausted, some fluid may remain on the front
face of head 210 and will continue to be drawn in until exhausted.
In any event, because of the value of the loading pressure as
discussed above, ambient atmosphere (air or nitrogen, for example)
does not then enter delivery chambers 217.
[0053] A dispensing sequence is then initiated in which processor
140 then causes the positioning system to position head 210 facing
substrate station 20, and particularly the mounted substrate 10,
and with head 210 at an appropriate distance from substrate 10. The
load setting of valve 94 is selected. Processor 140 then activates
ejectors 224 in a controlled sequence while causing the positioning
system to scan head 210 across substrate 10 line by line (or in
some other desired pattern), to dispense droplets in a
configuration which results in multiple arrays of the desired
configuration on substrate 10. If necessary or desired, processor
140 can repeat the load and dispensing sequences one or more
times.
[0054] Following a dispensing sequence, a purging sequence is
initiated by processor 140 causing the positioning system to
position head 210 facing, and in sealing engagement against, purge
station such that orifices 214 are in communication with vacuum
source 74. Processor 140 selects a neutral position of valves 84,
94 in which reservoir chamber 222 is essentially open to ambient
pressure, and opens valve 114 such that a predetermined quantity of
a purge fluid fills chambers 222, 217. Valve 114 is then closed and
valve 70 opened by processor 140, so that vacuum is thereby applied
from outside of orifices 214 resulting in purging of liquid in head
210 simultaneously out through orifices 214. After a suitable
predetermined time has elapsed to allow complete purging of head
210, processor 140 causes the positioning system to position head
210 at cleaning station 50, ensures valve 84 is closed selects the
holdoff setting of valve 94, and causes head 210 to wipe across
saturated pad 52 thereby cleaning plate 212 including the regions
around the orifices 214. During such operation, since the gas
pressure inside delivery chamber 217 exceeds the capillary
pressure, some outgassing will occur through orifices 214 (that is,
bubbling of gas exiting orifices will be seen there).
[0055] The above sequences can be repeated as often as desired for
a single substrate 10 or multiple different substrates (which may
be manually or automatically mounted and held on substrate station
20).
[0056] Where the ejectors are electrically resistive heating
elements, activation results in raising the temperature of the
heater to a temperature sufficient to vaporize a small portion of
the fluid immediately adjacent the heater and produce a bubble. The
temperature of the heater is raised to a temperature at least about
100.degree. C., usually at least about 400.degree. and more usually
at least about 700.degree. C., and the temperature may be raised as
high as 1000.degree. C. or higher, but is usually raised to a
temperature that does not exceed about 2000.degree. C. and more
usually does not exceed about 1500.degree. C. Accordingly, a
sufficient amount of energy will be delivered to the resistive
element to produce the requisite temperature rise, where the amount
of energy is generally in the range about 1.0 to 100 .mu.J, usually
about 1.5 to 15 .mu.J. The portion of fluid in the firing chamber
that is vaporized will be sufficient to produce a bubble in the
firing chamber of sufficient volume to force an amount of liquid
out of the orifice.
[0057] The formation of the bubble in the firing chamber traps a
portion or volume of the fluid present in the firing chamber
between the heating element and the orifice and forces an amount or
volume of fluid out of the orifice at high speed. The amount or
volume of fluid that is forced out of the firing chamber can be
controlled according to the quantity of biological material to be
deposited at the particular location on the receiving surface. As
is well known in the ink jet print art, the amount of fluid that is
expelled in a single activation event can be controlled by changing
one or more of a number of parameters, including the orifice
diameter, the orifice length (thickness of the orifice member at
the orifice), the size of the deposition chamber, and the size of
the heating element, among others. The amount of fluid that is
expelled during a single activation event is generally in the range
about 0.1 to 1000 pL, usually about 0.5 to 500 pL and more usually
about 1.0 to 250 pL. A typical velocity at which the fluid is
expelled from the chamber is more than about 1 m/s, usually more
than about 10 m/s, and may be as great as about 20 m/s or greater.
As will be appreciated, if the orifice is in motion with respect to
the receiving surface at the time an ejector is activated, the
actual site of deposition of the material will not be the location
that is at the moment of activation in a line-of-sight relation to
the orifice, but will be a location that is predictable for the
given distances and velocities.
[0058] Upon actuation of an ejector, as described above, fluid is
expelled from the orifice and travels to the substrate surface,
where it forms a spot on the substrate surface. In this manner, the
biological material (such as a nucleic acid) is deposited on the
substrate surface. As mentioned above, by varying the operating
parameters of the apparatus, the spot dimensions can be controlled
such that spots of various sizes can be produced. The sizes of the
spots (and, hence, of the array features) can have widths (that is,
diameter, for a round spot) in the range from a minimum of about 10
.mu.m to a maximum of about 1.0 cm. In embodiments where very small
spot sizes or feature sizes are desired, material can be deposited
according to the invention in small spots whose width is in the
range about 1.0 .mu.m to 1.0 mm, usually about 5.0 .mu.m to 500
.mu.m, and more usually about 10 .mu.m to 200 .mu.m.
[0059] Where a pattern of arrays is desired, any of a variety of
geometries may be constructed, including for example, organized
rows and columns of spots (for example, a grid of spots, across the
substrate surface), a series of curvilinear rows across the
substrate surface(for example, a series of concentric circles or
semi-circles of spots), and the like. An array according to the
invention generally includes at least tens of features, usually at
least hundreds, more usually thousands, and as many as a hundred
thousand or more features. Where a pattern of spots of an array is
deposited on a substrate surface, the pattern may vary as desired.
As such, the pattern may be in the form of organized rows and
columns of spots (for example, a grid of spots, across the
substrate surface), a series of curvilinear rows across the
substrate surface(for example, a series of concentric circles or
semi-circles of spots), and the like.
[0060] The present methods and apparatus may be used to deposit
biopolymers or other moieties on surfaces of any of a variety of
different substrates, including both flexible and rigid substrates.
Preferred materials provide physical support for the deposited
material and endure the conditions of the deposition process and of
any subsequent treatment or handling or processing that may be
encountered in the use of the particular array. The array substrate
may take any of a variety of configurations ranging from simple to
complex. Thus, the substrate could have generally planar form, as
for example a slide or plate configuration, such as a rectangular
or square or disc. In many embodiments, the substrate will be
shaped generally as a rectangular solid, having a length in the
range about 4 mm to 200, usually about 4 mm to 150 mm, more usually
about 4 mm to 125 mm; a width in the range about 4 mm to 200 mm,
usually about 4 mm to 120 mm and more usually about 4 mm to 80 mm;
and a thickness in the range about 0.01 mm to 5.0 mm, usually from
about 0.1 mm to 2 mm and more usually from about 0.2 to 1 mm. The
configuration of the array may be selected according to
manufacturing, handling, and use considerations.
[0061] The substrates may be fabricated from any of a variety of
materials. In certain embodiments, such as for example where
production of binding pair arrays for use in research and related
applications is desired, the materials from which the substrate may
be fabricated should ideally exhibit a low level of non-specific
binding during hybridization events. In many situations, it will
also be preferable to employ a material that is transparent to
visible and/or UV light. For flexible substrates, materials of
interest include: nylon, both modified and unmodified,
nitrocellulose, polypropylene, and the like, where a nylon
membrane, as well as derivatives thereof, may be particularly
useful in this embodiment. For rigid substrates, specific materials
of interest include: glass; plastics (for example,
polytetrafluoroethylene, polypropylene, polystyrene, polycarbonate,
and blends thereof, and the like); metals (for example, gold,
platinum, and the like).
[0062] The substrate surface onto which the polynucleotide
compositions or other moieties is deposited may be smooth or
substantially planar, or have irregularities, such as depressions
or elevations. The surface may be modified with one or more
different layers of compounds that serve to modify the properties
of the surface in a desirable manner. Such modification layers,
when present, will generally range in thickness from a
monomolecular thickness to about 1 mm, usually from a monomolecular
thickness to about 0.1 mm and more usually from a monomolecular
thickness to about 0.001 mm. Modification layers of interest
include: inorganic and organic layers such as metals, metal oxides,
polymers, small organic molecules and the like. Polymeric layers of
interest include layers of: peptides, proteins, polynucleic acids
or mimetics thereof (for example, peptide nucleic acids and the
like); polysaccharides, phospholipids, polyurethanes, polyesters,
polycarbonates, polyureas, polyamides, polyethyleneamines,
polyarylene sulfides, polysiloxanes, polyimides, polyacetates, and
the like, where the polymers may be hetero- or homopolymeric, and
may or may not have separate functional moieties attached thereto
(for example, conjugated), It will be appreciated from the above
description that the apparatus and method, by including a venturi
80, provides a simple way of providing negative or positive
backpressure in a pulse type fluid dispensing head while
conveniently isolating sensitive reagents to contaminants (such as
moisture). It will also be appreciated that variations and
modifications of the above described embodiments of the invention
are, of course, possible. Accordingly, the present invention is not
limited to such embodiments.
* * * * *