U.S. patent application number 10/611817 was filed with the patent office on 2004-02-26 for feature quality in array fabrication.
Invention is credited to Bass, Jay K..
Application Number | 20040039532 10/611817 |
Document ID | / |
Family ID | 23952610 |
Filed Date | 2004-02-26 |
United States Patent
Application |
20040039532 |
Kind Code |
A1 |
Bass, Jay K. |
February 26, 2004 |
Feature quality in array fabrication
Abstract
A method, and apparatus and computer program products for
executing the method. The method includes obtaining a set of
multiple images of a target feature location on an array of
multiple features, each image of the set representing the target
feature location following deposition of a corresponding sub-set of
multiple droplets for that feature. An overlay composite may be
generated from the image set. The overlay composite may be used as
a quality control tool, or in interrogating the array or processing
results of the interrogation.
Inventors: |
Bass, Jay K.; (Mountain
View, CA) |
Correspondence
Address: |
AGILENT TECHNOLOGIES, INC.
Legal Department, DL429
Intellectual Property Administration
P. O. Box 7599
Loveland
CO
80537-0599
US
|
Family ID: |
23952610 |
Appl. No.: |
10/611817 |
Filed: |
June 30, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10611817 |
Jun 30, 2003 |
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09491527 |
Jan 26, 2000 |
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6587579 |
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Current U.S.
Class: |
702/19 ;
422/68.1; 536/25.3; 702/27 |
Current CPC
Class: |
B01J 2219/0061 20130101;
B01J 2219/00659 20130101; B01J 2219/00605 20130101; B01J 2219/00608
20130101; B01J 2219/00662 20130101; C12Q 2565/513 20130101; B01J
2219/00689 20130101; C40B 60/14 20130101; B01J 2219/00529 20130101;
B01J 2219/00722 20130101; B01J 2219/00637 20130101; B01J 2219/00725
20130101; B01J 2219/00702 20130101; C40B 40/06 20130101; C12Q
2565/507 20130101; C12Q 1/6837 20130101; B01J 2219/00549 20130101;
B01J 2219/00612 20130101; B01J 2219/00378 20130101; C12Q 1/6837
20130101; B01J 2219/00693 20130101; C40B 40/10 20130101; G01N
33/54353 20130101; C40B 70/00 20130101; B01J 2219/00617 20130101;
B01J 2219/00695 20130101 |
Class at
Publication: |
702/19 ; 702/27;
536/25.3; 422/68.1 |
International
Class: |
G01N 033/48; C07H
021/00; G06F 019/00; G01N 015/06 |
Claims
What is claimed is:
1. A method comprising: obtaining a set of multiple images of a
target feature location on an array of multiple features, each
image of the set representing the target feature location following
deposition of a corresponding sub-set of multiple droplets for that
feature; and generating an overlay composite from the image
set.
2. A method according to claim 1 wherein the overlay composite
comprises a region of overlap of the droplet sub-sets.
3. A method according to claim 1 wherein: multiple image sets are
obtained of respective multiple target feature locations, each
image set representing a corresponding target feature location and
in which each image represents the location following deposition of
a corresponding droplet sub-set for that feature; and an overlay
composite is generated from each of the image sets.
4. A method of fabricating an array of features, comprising:
depositing multiple reagent droplets for each of multiple target
feature locations so as to form the array of features; obtaining a
set of multiple images of a target feature location, each image of
the set representing the target feature location following
deposition of a corresponding sub-set of multiple droplets for that
feature; and generating an overlay composite from the image
set.
5. A method according to claim 4 wherein the multiple reagent
droplets are ejected from a pulse-jet.
6. A method according to claim 4 wherein the overlay composite
comprises a region of overlap of the droplet sub-sets.
7. A method according to claim 4 wherein multiple image sets are
obtained of respective multiple target feature locations, each
image set representing a corresponding target feature location and
in which each image represents the location following deposition of
a corresponding sub-set of multiple droplets for that feature.
8. A method according to claim 7 wherein each set is obtained from
multiple captured images each of which simultaneously includes
multiple target feature locations following a cycle of droplet
depositions at those locations.
9. A method according to claim 4 wherein the array is a biopolymer
array.
10. A method according to claim 4 wherein the array is a
polynucleotide array and the set of images includes, for all
nucleotide droplets for the feature, an image representing the
target feature location following deposition of all droplets for a
corresponding one of the nucleotide monomers.
11. A method according to claim 4 additionally comprising either
altering the deposition of additional droplets for the feature, or
of droplets for other features on the same or another array, based
at least in part on the overlay composite.
12. A method according to claim 4 wherein the overlay composite is
stored on a storage medium and forwarded to a remote user of the
array.
13. A method of fabricating an array of features, comprising:
depositing multiple reagent droplets for each of multiple target
feature locations so as to form the array of features; obtaining a
set of multiple images of a target feature location, each image of
the set representing the target feature location following
deposition of a corresponding sub-set of multiple droplets for that
feature; and storing the set on a storage medium.
14. A method according to claim 13 wherein the multiple droplets
are deposited from a pulse-jet.
15. A method according to claim 13 wherein the set is stored on a
storage medium and forwarded to a remote user of the array.
16. A method according to claim 1 additionally comprising: exposing
the array to a sample; interrogating the array following the
exposure and optionally processing results of the interrogation;
wherein either the interrogation or processing is based at least in
part on the overlay composite.
17. A method according to claim 15 wherein a result of the
interrogation or processing is forwarded to a remote location.
18. A method comprising transmitting data representing a result of
the interrogation or processing from the method of claim 17.
19. An apparatus for fabricating an array of features, comprising:
a drop deposition system to deposit multiple reagent droplets for
each of multiple target feature locations so as to form the array
of features; an image capture system which provides a set of
multiple images of a target feature location, each image of the set
representing the target feature location following deposition of a
corresponding sub-set of multiple droplets for that feature; and a
processor which generates an overlay composite from the image
set.
20. An apparatus according to claim 19 wherein the drop deposition
system comprises a pulse-jet.
21. An apparatus according to claim 19 wherein the overlay
composite generated by the processor comprises a region of overlap
of the droplet sub-sets.
22. An apparatus according to claim 19 wherein the image capture
system provides multiple image sets of respective multiple target
feature locations, each image set representing a corresponding
target feature location and in which each image represents the
location following deposition of a corresponding sub-set of
multiple droplets for that feature.
23. An apparatus according to claim 22 wherein the image capture
system provides each set from multiple captured images each of
which simultaneously includes multiple target feature locations
following a cycle of droplet depositions at those locations.
24. An apparatus according to claim 19 wherein the array is a
polynucleotide array and the set of images includes, for multiple
nucleotide reagent droplets for the feature, an image representing
the target feature location following deposition of a corresponding
one of the nucleotide monomer droplets.
25. An apparatus according to claim 19 wherein the drop deposition
system alters the deposition of additional droplets for the
feature, or of droplets for other features on the same or another
array, based at least in part on the overlay composite.
26. An apparatus according to claim 19 additionally comprising a
storage medium and a communication module, wherein the processor
stores the overlay composite on the storage medium and causes the
communication module to communicate the stored overlay composite to
a remote user of the array.
27. An apparatus for fabricating an array of features, comprising:
a drop deposition system to deposit multiple reagent droplets for
each of multiple target feature locations so as to form the array
of features; an image capture system which provides a set of
multiple images of a target feature location, each image of the set
representing the target feature location following deposition of a
corresponding sub-set of multiple droplets for that feature; and a
storage medium onto which the image set or an overlay composite of
them are stored.
28. An apparatus according to claim 27, additionally comprising a
communication module to communicate the stored image set or an
overlay composite to a remote user of the array.
29. A computer program product comprising a computer readable
storage medium carrying computer readable program code, for use
with an apparatus for fabricating an array of features which
apparatus includes a drop deposition system and an image capture
system under the control of a computer, the program code when
loaded into the computer performing the steps of: depositing
multiple reagent droplets from the drop deposition system for each
of multiple target feature locations, so as to form an array of
features; obtaining from the image capture system, a set of
multiple images of a target feature location on an array of
multiple features, each image of the set representing the target
feature location following deposition of a corresponding sub-set of
multiple droplets for that feature; and generating in the computer
an overlay composite from the image set.
30. A computer program product comprising a computer readable
storage medium carrying computer readable program code, for use
with an apparatus having a data retrieval unit under the control of
a computer, the program code when loaded into the computer
performing the steps of: obtaining through the data retrieval unit
a set of multiple images of a target feature location on an array
of multiple features, each image of the set representing the target
feature location following deposition of a corresponding sub-set of
multiple droplets for that feature; and generating in the computer
an overlay composite from the image set.
31. A computer program product according to claim 30 wherein the
program code generates an overlay composite comprising a region of
overlap of the multiple droplets.
32. A computer program product according to claim 30 wherein:
multiple image sets are obtained of respective multiple target
feature locations, each image set representing a corresponding
target feature location and in which each image represents the
location following deposition of a corresponding sub-set of
multiple droplets for that feature; and an overlay composite is
generated in the computer from each of the image sets.
33. A computer program product according to claim 30 wherein the
program code additionally either alters the deposition of
additional droplets for the feature, or of droplets for other
features on the same or another array, based at least in part on
the overlay composite.
34. A computer program product according to claim 30 wherein the
program code additionally performs the step of: controlling at
least in part, interrogation of the array following exposure to a
sample; and optionally processing results of the interrogation;
wherein either the interrogation or processing is based at least in
part on the overlay composite.
Description
FIELD OF THE INVENTION
[0001] This invention relates to 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] Polynucleotide arrays (such as DNA or RNA arrays), are known
and are used, for example, as diagnostic or screening tools. Such
arrays include regions of usually different sequence
polynucleotides arranged in a predetermined configuration on a
substrate. These regions (sometimes referenced as "features") are
positioned at respective locations ("addresses") on the substrate.
The arrays, when exposed to a sample, will exhibit an observed
binding pattern. This binding pattern can be detected upon
interrogating the array. For example all polynucleotide targets
(for example, DNA) in the sample can be labeled with a suitable
label (such as a fluorescent compound), and the fluorescence
pattern on the array accurately observed following exposure to the
sample. Assuming that the different sequence polynucleotides were
correctly deposited in accordance with the predetermined
configuration, then the observed binding pattern will be indicative
of the presence and/or concentration of one or more polynucleotide
components of the sample.
[0003] Biopolymer arrays can be fabricated by depositing previously
obtained biopolymers (such as from synthesis or natural sources)
onto a substrate, or by in situ synthesis methods. Methods of
depositing obtained biopolymers include loading then touching a pin
or capillary to a surface, such as described in U.S. Pat. No.
5,807,522 or deposition by firing from a pulse jet such as an
inkjet head, such as described in PCT publications WO 95/25116 and
WO 98/41531, and elsewhere. For in situ fabrication methods,
multiple different reagent droplets are deposited at a given target
location in order to form the final feature (hence a probe of the
feature is synthesized on the array stubstrate). The in situ
fabrication methods include those described in U.S. Pat. No.
5,449,754 for synthesizing peptide arrays, and described in WO
98/41531 and the references cited therein for polynucleotides. The
in situ method for fabricating a polynucleotide array typically
follows, at each of the multiple different addresses at which
features are to be formed, the same conventional iterative sequence
used in forming polynucleotides from nucleoside reagents on a
support by means of known chemistry. This iterative sequence is as
follows: (a) coupling a selected nucleoside through a phosphite
linkage to a functionalized support in the first iteration, or a
nucleoside bound to the substrate (i.e. the nucleoside-modified
substrate) in subsequent iterations; (b) optionally, but
preferably, blocking unreacted hydroxyl groups on the substrate
bound nucleoside; (c) oxidizing the phosphite linkage of step (a)
to form a phosphate linkage; and (d) removing the protecting group
("deprotection") from the now substrate bound nucleoside coupled in
step (a), to generate a reactive site for the next cycle of these
steps. The functionalized support (in the first cycle) or
deprotected coupled nucleoside (in subsequent cycles) provides a
substrate bound moiety with a linking group for forming the
phosphite linkage with a next nucleoside to be coupled in step (a).
Final deprotection of nucleoside bases can be accomplished using
alkaline conditions such as ammonium hydroxide, in a known
manner.
[0004] The foregoing chemistry of the synthesis of polynucleotides
is described in detail, for example, in Caruthers, Science 230:
281-285, 1985; Itakura et al., Ann. Rev. Biochem. 53: 323-356;
Hunkapillar et al., Nature 310: 105-110, 1984; and in "Synthesis of
Oligonucleotide Derivatives in Design and Targeted Reaction of
Oligonucleotide Derivatives", CRC Press, Boca Raton, Fla., pages
100 et seq., U.S. Pat. No. 4,458,066, U.S. Pat. No. 4,500,707, U.S.
Pat. No. 5,153,319, U.S. Pat. No. 5,869,643, EP 0294196, and
elsewhere The phosphoramidite and phosphite triester approaches are
most broadly used, but other approaches include the phosphodiester
approach, the phosphotriester approach and the H-phosphonate
approach. The substrates are typically functionalized to bond to
the first deposited monomer. Suitable techniques for
functionalizing substrates with such linking moieties are
described, for example, in Southern, E. M., Maskos, U. and Elder,
J. K., Genomics, 13, 1007-1017, 1992.
[0005] In the case of array fabrication, different monomers may be
deposited at different addresses on the substrate during any one
iteration so that the different features of the completed array
will have different desired biopolymer sequences. One or more
intermediate further steps may be required in each iteration, such
as the conventional oxidation and washing steps in the case of in
situ fabrication of polynucleotide arrays.
[0006] In array fabrication, the quantities of polynucleotide
available are usually very small and expensive. Additionally,
sample quantities available for testing are usually also very small
and it is therefore desirable to simultaneously test the same
sample against a large number of different probes on an array.
These conditions require use of arrays with large numbers of very
small, closely spaced features. It is important in such arrays that
features actually be present, that they are put down accurately in
the desired target pattern, are of the correct size, and that the
DNA is uniformly coated within the feature. If any of these
conditions are not met within a reasonable tolerance, and the array
user is not aware of deviations outside such tolerance, the results
obtained from a given array may be unreliable and misleading. This
of course can have serious consequences to diagnostic, screening,
gene expression analysis or other purposes for which the array is
being used. However, in any system used to fabricate arrays with
the required small features, there is inevitably some degree of
error, either fixed (and hence repeated) and/or random. The present
invention realizes that in the special case of in situ fabrication
method or any other method requiring deposition of multiple
droplets at a target feature location, drop deposition errors from
cycle to cycle may be different and are cumulative in determining
errors in the finally formed features.
[0007] It would be desirable then to provide a means by which
errors in features resulting during an in situ or any array
fabrication method requiring multiple droplet deposition for a
target feature location, can be readily determined.
SUMMARY OF THE INVENTION
[0008] The present invention further realizes that in array
fabrication using the in situ method or any method using multiple
drop deposition for a target feature location, the final error in a
feature is a sum of errors during respective droplet depositions,
and that such individual droplet errors may vary during each cycle
at a given feature. Such errors may either be fixed or random. For
example, in the fabrication of a polynucleotide array using
phosphoramidite chemistry, different drop dispensers (such as pulse
jets which eject drops drops toward a surface) may be provided to
deposit different phosphoramidite droplets. Each nozzle may have
its own inherent fixed drop dispensing error (such as error in drop
dispenser position within a head, droplet size, or direction of
drop). Also, the positioning system may have fixed inherent errors.
Further, random errors can occur which are different during the
dispensing of any one droplet. For example, air currents may vary
during different droplet dispensing steps, or ambient temperature
variations may cause expansion/contraction in dispensing apparatus
components which affects absolute and/or relative positions of
dispensed droplets. Thus, an error in the final feature may be a
sum of errors from individual drop deposition at each feature. The
present invention provides a means of tracking such individual
droplet deposition error for a feature and using such multiple drop
deposition error for that feature to determine an overall feature
error.
[0009] In one aspect, the present invention provides a method which
includes obtaining a set of multiple images of a target feature
location on an array of multiple features. Each image of the set
represents the target feature location following deposition of a
corresponding sub-set of multiple droplets for that feature. An
overlay composite is generated from the image set. Note that the
processing for this can be done as each image of a set is obtained
or after all images of a set are obtained. By an "overlay
composite" in this context is referenced that information from at
least one same location on the set of images is combined or
compared using some function (for example, logical AND or some
other operation). The same location may be, for example, all of the
target feature location plus some predetermined area around that
location, or just some point or portion of the foregoing. A
particular overlay composite comprises a region of overlap of the
multiple droplets. One or more feature characteristics (for
example, the extent, size, shape or location of overlap of
deposited droplets) may be provided by the overlay composite.
Typically, since an array will usually contain many features and it
will be desirable to determine feature characteristics of multiple
such features (and perhaps all of them), the method may be used by
obtaining multiple image sets of respective multiple target feature
locations. In this case each image set represents a corresponding
target feature location with each image of the set representing the
location following deposition of a corresponding sub-set of
multiple droplets for that feature. An overlay composite may then
be generated from each of the image sets.
[0010] The above aspect may be used in the fabrication of arrays,
or by an end user of the array or elsewhere. When the method is
used in fabrication, it will also typically include depositing
multiple reagent droplets for each of multiple target feature
locations so as to form array of features, and obtaining the image
sets during such fabrication. In the fabrication, the image set is
typically obtained by capturing an image of each target feature
location following deposition of a corresponding drop sub-set (for
example, from multiple captured images each of which simultaneously
includes multiple target feature locations following a cycle of
droplet depositions at those locations). When the above aspect is
used by an end user or elsewhere, the image sets may be obtained by
other means (such as from a portable data storage medium associated
with the array and carrying the image sets as digital data, or from
communication with a remote array fabricator).
[0011] The overlay composite can be used for any of a number of
purposes. For example, the overlay composite may also be used by
the fabricator as a quality control tool such as by rejecting
arrays with one or more feature characteristics which do not meet
predetermined requirements, and/or by altering the deposition of
additional droplets for the feature, or of droplets for other
features on the same or another array. Such rejecting or altering
may be based at least in part on the overlay composite.
Additionally, the overlay composite may be forwarded to a remote
user of the array for use by them in interrogating the array or
processing data resulting from the interrogation. Typically, the
remote user will expose the array to a sample, interrogate the
array following the exposure and optionally process the results of
the evaluation (such as for evaluating the sample composition, for
example, for the presence of a component). The interrogation or
processing may be based at least in part on the overlay composite.
However, in an alternative aspect of the present invention, rather
than (or in addition to) forwarding the composite overlay to the
remote user, the image sets themselves may be stored on a storage
medium and forwarded to the remote user (such as by hard copy or on
a portable digital data storage medium, or by communication). Any
forwarding to the remote user may be, for example, be by hard copy
or portable digital data storage medium carrying the required
information, or by communication over a suitable communication
channel.
[0012] The present invention also provides an apparatus for
fabricating an array in accordance with any of the methods of the
invention. The apparatus may include a drop deposition system to
deposit multiple reagent droplets for each of multiple target
feature locations so as to form the array of features. An image
capture system provides the one or more sets of multiple images
previously referenced. The apparatus may further include either a
processor which generates an overlay composite from the image set
and optionally performs any the processing previously described, or
a storage medium onto which the image set or an overlay composite
of them are stored, or both. Optionally, a communication module is
present to communicate an image set or overlay composite to a
remote location.
[0013] The present invention further provides a computer readable
storage medium carrying program code which can be used with an
apparatus of the present invention, to cause it to execute the
steps of a method of the present invention.
[0014] The various aspects of the present invention can provide any
one or more of the following and/or other useful benefits. For
example, individual droplet deposition errors during an in situ or
any array fabrication method requiring multiple droplet deposition
for a target feature location, can be readily determined and
tracked, and resultant feature errors determined from those
individual droplet errors. Such results can be used as quality
control tools during array fabrication and/or forwarded to a remote
location for use in interrogating or processing interrogation
results from the corresponding array.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 illustrates a substrate carrying multiple arrays,
such as may be fabricated by methods of the present invention;
[0016] FIG. 2 is an enlarged view of a portion of FIG. 1 showing
multiple ideal spots or features;
[0017] FIG. 3 is an enlarged illustration of a portion of the
substrate in FIG. 2;
[0018] FIGS. 4 and 5 illustrate examples of formation of overlay
composites for less than ideal features;
[0019] FIG. 6 is a schematic diagram of a fabrication apparatus and
method of the present invention; and
[0020] FIG. 7 is a schematic diagram of an apparatus at a user site
which can execute a method of the present invention.
[0021] To facilitate understanding, identical reference numerals
have been used, where practical, to designate identical elements
that are common to the figures.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0022] In the present application, unless a contrary intention
appears, the following terms refer to the indicated
characteristics. A "biopolymer" is a polymer of one or more types
of repeating units. Biopolymers are typically found in biological
systems and particularly include peptides or polynucleotides, as
well as such compounds composed of or containing amino acid analogs
or non-amino acid groups, or nucleotide analogs or non-nucleotide
groups. This includes polynucleotides in which the conventional
backbone has been replaced with a non-naturally occurring or
synthetic backbone, and nucleic acids (or synthetic or naturally
occurring analogs) in which one or more of the conventional bases
has been replaced with a group (natural or synthetic) 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 sub-unit of a
nucleic acid and has a phosphate group, a 5 carbon sugar and a
nitrogen containing base, as well as functional analogs (whether
synthetic or naturally occurring) of such sub-units which in the
polymer form (as a polynucleotide) can hybridize with naturally
occurring polynucleotides in a sequence specific manner analogous
to that of two naturally occurring polynucleotides. For example, a
"biopolymer" includes DNA (including cDNA), RNA, oligonucleotides,
and PNA and other polynucleotides as described in U.S. Pat. No.
5,948,902 and references cited therein (all of which are
incorporated herein by reference), regardless of the source. 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 liquid containing either a
biomonomer or biopolymer, respectively (typically in solution).
[0023] An "array", unless a contrary intention appears, includes
any one or two dimensional arrangement of addressable regions
bearing a particular chemical moiety to moieties (for example,
biopolymers such as polynucleotide sequences) associated with that
region. An array is "addressable" in that it has multiple regions
of different moieties (for example, different polynucleotide
sequences) such that a region (a "feature" or "spot" of the array)
at a particular predetermined location (an "address") on the array
will detect a particular target or class of targets (although a
feature may incidentally detect non-targets of that feature). Array
features are typically, but need not be, separated by intervening
spaces. In the case of an array, the "target" will be referenced as
a moiety in a mobile phase (typically fluid), to be detected by
probes ("target probes") which are bound to the substrate at the
various regions. However, either of the "target" or "target probes"
may be the one which is to be evaluated by the other (thus, either
one could be an unknown mixture of polynucleotides to be evaluated
by binding with the other). An "array layout" refers collectively
to one or more characteristics of the features, such as feature
positioning, one or more feature dimensions, and some indication of
a moiety at a given location. "Hybridizing" and "binding", with
respect to polynucleotides, are used interchangeably.
[0024] When one item is indicated as being "remote" from another,
this is referenced that the two items are at least in different
buildings, and may be at least one mile, ten miles, or at least one
hundred miles apart. "Communicating" information references
transmitting the data representing that information over a suitable
communication channel (for example, a private or public network).
"Forwarding" an item refers to any means of getting that item from
one location to the next, whether by physically transporting that
item and includes, at least in the case of data, physically
transporting a medium carrying the data or communicating the data.
An array "package" may be the array plus only a substrate on which
the array is deposited, although the package may include other
features (such as a housing with a chamber). A "chamber" references
an enclosed volume (although a chamber may be accessible through
one or more ports). It will also be appreciated that throughout the
present application, that words such as "top", "upper", and "lower"
are used in a relative sense only. "Fluid" is used herein to
reference a liquid. An "image" in relation to a target feature
location following droplet deposition, refers to data on shape,
size or position of the whole or part of the droplet (in liquid
form or after drying), regardless of how such data was obtained
(for example by capturing with a camera, or by scanning with a
laser beam, or by some other means). A "set" or a "sub-set" may
have one or more members (for example, one or more droplets).
Reference to a singular item, includes the possibility that there
are plural of the same items present. All patents and other cited
references are incorporated into this application by reference.
[0025] Referring first to FIGS. 1-3, typically methods and
apparatus of the present invention generate or use a contiguous
planar substrate 10 carrying one or more arrays 12 disposed across
a front surface 11a of substrate 10 and separated by inter-array
areas 13. A back side 11b of substrate 10 does not carry any arrays
12. The arrays on substrate 10 can be designed for testing against
any type of sample, whether a trial sample, reference sample, a
combination of them, or a known mixture of polynucleotides (in
which latter case the arrays may be composed of features carrying
unknown sequences to be evaluated). Each array 12 has associated
with it a unique identification in the form of a bar code 356.
While ten arrays 12 are shown in FIG. 1 and the different
embodiments described below may use substrates with particular
numbers of arrays, it will be understood that substrate 10 and the
embodiments to be used with it, may use any number of desired
arrays 12. Similarly, substrate 10 may be of any shape, and any
apparatus used with it adapted accordingly. Depending upon intended
use, any or all of arrays 12 may be the same or different from one
another and each will contain multiple spots or features 16 of
biopolymers in the form of polynucleotides. A typical array may
contain from more than ten, more than one hundred, more than one
thousand or ten thousand features, or even more than from one
hundred thousand features. All of the features 16 may be different,
or some or all could be the same. In the embodiment illustrated,
there are interfeature areas 17 between features, which do not
carry any polynucleotide. It will be appreciated though, that the
interfeature areas 17 could be of various sizes and configurations.
It will be appreciated that there need not be any space separating
arrays 12 from one another, nor features 16 within an array from
one another. However, in the case where arrays 12 are formed by the
conventional in situ method as described above, by depositing for
each feature a droplet of reagent in each step such as by using a
pulse jet such as an inkjet type head, such interfeature areas 17
will typically be present. Each feature carries a predetermined
polynucleotide (which includes the possibility of mixtures of
polynucleotides). As per usual, A, C, G, T represent the usual
nucleotides. It will be understood that there is usually a linker
molecule (not shown) of any known types between the front surface
11a and the first nucleotide.
[0026] FIGS. 2 and 3 illustrate ideal features where the actual
features formed are the same as the target (or "aim") features,
with each feature 16 being uniform in shape, size and composition,
and the features being regularly spaced. Such an array when
fabricated by the in situ method, would require all reagent
droplets for each feature to be uniform in shape and accurately
deposited at the target feature location. In practice, such an
ideal result is difficult to obtain due to both the fixed and
random errors such as those discussed above. FIG. 4 shows images of
two phosphoramidite droplets deposited in different cycles, for a
particular feature (that is FIG. 4 shows an image set for that
feature), and illustrates a less than ideal result. FIG. 5
similarly illustrates an image set for another feature of five
phosphoramidite droplets with a less than ideal actual feature
being formed (reference to the shape of the deposited droplets
will, in the following discussion, refer to dried droplet shape).
The droplet errors illustrated in FIGS. 4 and 5 have been somewhat
exaggerated for the purpose of clarity. For the discussion which
follows, it will be assumed that each "sub-set" of droplets after
which an image is captured, consists of only one set. However, in
practice each such sub-set will typically consist of multiple
droplets of the same composition. In FIG. 4, a nucleoside
phosphoramidite reagent droplet 404 (such droplets being often
referenced simply as "phosphoramidite" droplets) of circular shape
has been deposited in one cycle with its center exactly at the
center 402 of the target feature location. However, another
phosphoramidite droplet 400 deposited in a subsequent or earlier
cycle has an elliptical shape due to fixed or random errors, and
has its center mis-aligned with target feature center 402. If the
target feature was only to be formed from the foregoing two
phosphoramidites, the actual feature having the desired nucleotide
sequence would only consist of overlap region 406 (which is the
intersection of the droplets, or logical AND of them), which is
neither of the target circular shape nor on the target feature
center. Similarly, in FIG. 5 where five phosphoramidites droplets
410, 416, 418, 422 are deposited in different cycles for a target
feature, one droplet 410 is centered on target feature center 412
and is correctly shaped (circular) but is too large, while droplets
416, 418 have the target shape and size but are off the center 412,
and droplet 422 is both of the wrong shape, size and position. In
this case, the resulting actual feature 430 of five nucleotides in
length, would again be the overlap (or logical AND) of the
droplets. Note that actual feature 430 is of incorrect shape and
size, and does not even overlap the target center 412.
[0027] Thus, as illustrated in FIGS. 4 and 5, when an image of each
of the deposited reagent droplets in the multi-cycle in situ
synthesis are obtained (such as by obtaining an image of each
entire droplet), formation of an overlay composite can provide
information on one or more characteristics of an actual feature. In
the particular cases described in connection with FIGS. 4 and 5, a
logical AND operation is applied to the set of such images for a
given feature to provide the overlap region characteristics (such
as size, shape and location) and hence the characteristics of the
actual feature. As is apparent from FIGS. 4 and 5, overlay
composites formed from a logical AND operation, automatically
provides an evaluation of feature characteristics.
[0028] Referring now to FIG. 6, an apparatus of the present
invention which can execute a method of the present invention, will
now be described.
[0029] Referring now to FIG. 6 the apparatus shown includes a
substrate station 20 on which can be mounted a substrate 10. Pins
or similar means (not shown) can be provided on substrate station
20 by which to approximately align substrate 10 to a nominal
position thereon. Substrate station 20 can include a vacuum chuck
connected to a suitable vacuum source (not shown) to retain a
substrate 14 without exerting too much pressure thereon, since
substrate 14 is often made of glass. A flood station 68 is provided
which can expose the entire surface of substrate 10, when
positioned beneath station 68 as illustrated in broken lines in
FIG. 4, to a fluid typically used in the in situ process, and to
which all features must be exposed during each cycle (for example,
oxidizer, deprotection agent, and wash buffer).
[0030] A dispensing head 210 is retained by a head retainer 208.
The positioning system includes a carriage 62 connected to a first
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 station 20 (and hence mounted substrate 10) facing
the dispensing head 210, by moving it in the direction of arrow 63,
while transporter 100 is used to provide adjustment of the position
of head retainer 208 (and hence head 210) in a direction of axis
204. In this manner, head 210 can be scanned line by line, by
scanning along a line over substrate 10 in the direction of axis
204 using transporter 100, while line by line movement of substrate
10 in a direction of axis 63 is provided by transporter 60.
Transporter 60 can also move substrate holder 20 to position
substrate 10 beneath flood station 68 (as illustrated by the
substrate 10 shown in broken lines in FIG. 4). Head 210 may also
optionally be moved in a vertical direction 202, by another
suitable transporter (not shown). It will be appreciated that other
scanning configurations could be used. It will also be appreciated
that both transporters 60 and 100, or either one of them, with
suitable construction, could be used to perform the foregoing
scanning of head 210 with respect to substrate 10. 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
or substrate 10) it will be understood that any required moving can
be accomplished by moving either element or a combination of both
of them. The head 210, the positioning system, and processor 140
together act as the deposition system of the apparatus. An encoder
30 communicates with processor 140 to provide data on the exact
location of substrate station 20 (and hence substrate 10 if
positioned correctly on substrate station 20), while encoder 34
provides data on the exact location of holder 208 (and hence head
210 if positioned correctly on holder 208). Any suitable encoder,
such as an optical encoder, may be used which provides data on
linear position.
[0031] Processor 140 also has access through a communication module
144 to a communication channel 180 to communicate with a remote
station. Communication channel 180 may, for example, be a Wide Area
Network ("WAN"), telephone network, satellite network, or any other
suitable communication channel.
[0032] Head 210 may be of a type commonly used in an ink jet type
of printer and may, for example, include five or more chambers (at
least one for each of four nucleoside phosphoramidite monomers plus
at least one for an activator solution) each communicating with a
corresponding set of multiple drop dispensing orifices and multiple
ejectors which are positioned in the chambers opposite respective
orifices. Each ejector is in the form of an electrical resistor
operating as a heating element under control of processor 140
(although piezoelectric elements could be used instead). Each
orifice with its associated ejector and portion of the chamber,
defines a corresponding pulse jet. It will be appreciated that head
210 could, for example, have more or less pulse jets as desired
(for example, at least ten or at least one hundred pulse jets).
Application of a single electric pulse to an ejector will cause a
droplet to be dispensed from a corresponding orifice. Certain
elements of the head 210 can be adapted from parts of a
commercially available thermal inkjet print head device available
from Hewlett-Packard Co. as part no. HP51645A. Alternatively,
multiple heads could be used instead of a single head 210, each
being similar in construction to head 210 and being provided with
respective transporters under control of processor 140 for
independent movement. In this alternate configuration, each head
may dispense a corresponding biomonomer (for example, one of four
nucleoside phosphoramidites) or an activator solution.
[0033] As is well known in the ink jet print art, the amount of
fluid that is expelled in a single activation event of a pulse jet,
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.
[0034] The apparatus can deposit droplets to provide features which
may 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.
[0035] The apparatus further includes a display 310, speaker 314,
and operator input device 312. Operator input device 312 may, for
example, be a keyboard, mouse, or the like. Processor 140 has
access to a memory 141, and controls print head 210 (specifically,
the activation of the ejectors therein), operation of the
positioning system, operation of each jet in print head 210, and
operation of display 310 and speaker 314. Memory 141 may be any
suitable device in which processor 140 can store and retrieve data,
such as magnetic, optical, or solid state storage devices
(including magnetic or optical disks or tape or RAM, or any other
suitable device, either fixed or portable). Processor 140 may
include a general purpose digital microprocessor suitably
programmed from a computer readable medium carrying necessary
program code, to execute all of the steps required by the present
invention, or any hardware or software combination which will
perform those or equivalent steps. The programming can be provided
remotely to processor 141, or previously saved in a computer
program product such as memory 141 or some other portable or fixed
computer readable storage medium using any of those devices
mentioned below in connection with memory 141. For example, a
magnetic or optical disk 324a may carry the programming, and can be
read by disk writer/reader 326.
[0036] A writing system which is under the control of processor
140, includes a writer in the form of a printer 150 which can write
identifications onto substrate 10 by printing them in the form of
the bar codes 356 (or alternatively on a housing carrying the
substrate) each in association with a corresponding array 12 as
shown in FIG. 1. Printer 150 may accomplish this task before or
after formation of the array by the drop deposition system. The
writing system further includes a data writer/reader 326 (such as
an optical or magnetic disk drive) which can write data to a
portable computer readable storage medium (such as an optical or
magnetic disk). A cutter 152 is provided to cut substrate 10 into
individual array units 15 each carrying a corresponding array 12
and bar code 356. An illumination source 170 can direct light
through a beam splitter in the form of dichroic mirror 172 to
illuminate substrate 10 on station 20 from below (the light shining
through the back side 11b of substrate 10). An image capture system
in the form of linescan camera 174 and processor 140, captures
images through mirror 172 each of which simultaneously includes
multiple target feature locations on substrate 10 following a cycle
of droplet depositions at those locations. Processor 140 can
extract from such captured images, the image set for each target
feature location plus some predetermined region around that
location (for example, a square surrounding that location) images
each of which simultaneously includes multiple target feature
locations following a cycle of droplet depositions at those
locations. Camera 174 may have a pixel resolution of 30 .mu.m or
less, or 20 .mu.m or less, and more preferably 10 .mu.m or less.
Any suitable camera may be used such as a CCD camera capturing a
rectangular image, or a linescan camera. Processor 140 coordinates
capture of the lines with the movement of substrate 10 during
deposition of the reagent droplets.
[0037] The above described components in FIG. 6 represent an
apparatus for producing an addressable array, which is sometimes
referenced herein as a "fabrication station". FIG. 7 illustrates an
apparatus for receiving an addressable array, in particular a
single "user station", which is remote from the fabrication
station. The user station includes a processor 162, a memory 184, a
scanner 160 which can interrogate an array, data writer/reader 186
(which may be capable of writing/reading to the same type of media
as writer/reader 320), and a communication module 164 which also
has access to communication channel 180. Memory 184 can be any type
of memory such as those used for memory 141. Scanner 160 can be any
suitable apparatus for interrogating an array, such as one which
can read the location and intensity of fluorescence at each feature
of an array following exposure to a fluorescently labeled sample.
For example, such a scanner may be similar to the GENEARRAY scanner
available from Hewlett-Packard, Palo Alto, Calif. Scanner 160 also
includes though, a first bar code reader to read a each bar code
356 appearing on segment 15.
[0038] It will be understood that there may be multiple such user
stations, each remote from the fabrication station and each other,
in which case the fabrication station acts as a central fabrication
station (that is, a fabrication station which services more than
one remote user station at the same or different times). One or
more such user stations may be in communication with the
fabrication station at any given time. It will also be appreciated
that processors 140 and 162 can be programmed from any computer
readable medium carrying a suitable computer program. For example,
such a medium can be any memory device such as those described in
connection with memory 141, and may be read locally (such as by
reader/writer 320 in the case of processor 140 or writer/reader 186
in the case of processor 162) or from a remote location through
communication channel 180.
[0039] The operation of the fabrication station will now be
described. It will be assumed that a substrate 10 on which arrays
12 are to be fabricated, is in position on station 20 and that
processor 140 is programmed with the necessary layout information
to fabricate target arrays 12. Processor 140 will generate a unique
identification for each array 12 in the form of a corresponding bar
code 356. Each identifier may be stored in memory 141 in
association with the corresponding image sets for each feature of
an array 12, or with composite overlays derived from those sets by
processor 140 (as mentioned below).
[0040] Processor 140 controls fabrication, as described above, to
generate the one or more arrays on substrate 10 by depositing for
each target feature, multiple droplets of phosphoramidite reagents,
and sends substrate 10 to flood station 68 for intervening or final
steps as required, all in accordance with the conventional in situ
polynucleotide array fabrication process described above.
Preferably at each feature, during any one cycle multiple droplets
of both the same phorsphoramidite solution and a tetrazole
activator are deposited. For example, about five droplets of each
may be deposited (making for a total of ten droplets in each
cycle). Camera 174 captures images through mirror 172 each of which
simultaneously includes multiple target feature locations on
substrate 10 following a cycle of droplet depositions at those
locations. The sub-set of droplets after which each image can be
captured can equal this total number. However, it will be
appreciated that this need not be the case (for example, ten total
droplets may be deposited during a cycle, with an image being
captured after each sub-set of five droplets, which two images are
processed to determine total deposition area with a logical OR).
Processor 140 extracts from such captured images, the image set for
each target feature location plus some predetermined region around
that location. At this point, if it is desired to provide feature
characteristic information to an array user, processor 140 may
store such image sets for all features of an array 12 into memory
141, or more preferably generates an overlay composite from all the
sets (preferably by a logical AND operation as described above) and
stores the overlay composites for all the features of an array 12
into memory 141. In either event, the image sets or overlay
composites for an array 12 are stored in association with the
corresponding unique identifier for that array. Note that the
generation of an overlay composite can be performed after all
images of a set are collected, or data processing can be performed
as the images are obtained (that is, each image is processed as
required immediately after it is obtained). Optionally, the overlay
composites for an array or the image sets themselves, can later be
stored onto a portable storage medium 324b in association with the
corresponding array unique identification, by writer/reader 326 for
provision to a remote user. Note that the overlay composites
effectively represent a map of actual features on the array. It
will be understood that the data form of the overlay composites can
be varied though, such as being absolute data or relative data
(such as relating the actual feature map to a corresponding target
feature map forwarded from the fabrication station).
[0041] If it is not desired to provide overlay composites to an
array user, but only to use the overlay composites as a quality
control measure, then they can be used to reject an array 12 and
direct it toward a garbage bin (not shown) if one or more
predetermined number of features have one or more characteristics
outside a predetermined tolerance. Such characteristics may include
a minimum feature size (note that a feature size would be
considered zero where the images indicate a complete failure to
deposit a required phosphoramidite reagent during any one cycle).
In an alternative, the deposition of additional droplets for a
selected feature or droplets deposited at other features on the
same or another array, can be based at least in part on an
evaluated characteristic from an overlay composite for other
droplets for that selected or other features. For example, if
processor 140 generates logical AND for image sets of all features
in an array and determines the resulting features have a
characteristic outside a predetermined limit, such as a common
mispositioning error, processor 140 may be able to compensate for
this by repositioning head 210 during fabrication of other arrays.
Other functions can be used, such as a logical "OR" where all of
the area which has been covered by the various deposition cycles
can be determined. The result of a logical "OR" shows the region
where both full-length and non full-length polynucleotides are
obtained (which can be helpful with, for example, HPLC analysis of
DNA fragments)
[0042] It will be appreciated also, and any of the foregoing uses
of the overlay composites can be combined. For example overlay
composites can be both used to reject an array as described above,
and the overlay composites or image sets still stored and forwarded
to an end user for arrays that were not rejected. Furthemore,
information from the image sets can be used for other purposes,
such as monitoring variation in the size of a deposited droplet
sub-set (which may indicate a problem).
[0043] Either before array fabrication on substrate 10 has been
commenced, or after it has been completed, substrate 10 may be sent
to writer 150 which, under control of processor 140, writes the
unique bar codes 356 on substrate 10 each in association with its
corresponding array (by being physically close to it in the manner
shown in FIG. 1). The substrate 10 is then sent to a cutter 152
wherein portions of substrate 10 carrying an individual array 12
and its associated local identifier 356 are separated from the
remainder of substrate 10, to provide multiple array units 15. The
array unit 15 is placed in package 340 with storage medium 324b (if
used) carrying overlay composites or image sets for the
corresponding array 12, and the package then shipped to a remote
user station.
[0044] The above sequence can be repeated at the fabrication
station as desired for multiple substrates 10 in turn. As mentioned
above, the fabrication station may act as a central fabrication
station for each of multiple remote user stations, in the same
manner as described above. Whether or not the fabrication station
acts as a central fabrication station, it can optionally maintain a
database of unique array identifiers in memory 141, each in
association with the corresponding image sets or overlay
composites.
[0045] At the user station of FIG. 7, the resulting package 340 is
then received from the remote fabrication station. A sample, for
example a test sample, is exposed to the array 12 on the array unit
15 received in package 340. Following hybridization and washing in
a known manner, the array is then inserted into scanner 160 and
interrogated by it to obtain interrogation results (such as
information representing the fluorescence pattern on the array 12).
The first reader in scanner 160 also reads the identifier 356
present on the array substrate 10 in association with the
corresponding array 12. Using identifier 356, processor 162 may
then obtain the corresponding overlay composites or image sets for
array 12 from portable storage medium 324b or from the database of
such information in memory 141 by communicating with that database
through communication module 164 and communication channel 180.
Alternatively, in the case where processor 162 has only obtained
image sets, it can generate an overlay composite itself as
needed.
[0046] Once processor 162 has obtained the overlay composites or
image sets for an array 12, it can then control interrogation of
the corresponding array by scanner 160 and/or the processing of the
results of the interrogation, using such information. For example,
an overlay composite may indicate a specific feature of such low
quality (that is, having a characteristic outside a predetermined
range) which is redundant with another feature, such that the
scanner need not interrogate that specific feature for a given
test, or alternatively that information read from that address can
be ignored or deleted as useless. Following array interrogation,
further processing of the interrogation results can be performed to
evaluate the sample composition (such as for a specific target)
based on the results of the interrogation. This further processing
can be done by processor 162 or by a user examining the
interrogation results. The interrogation results (raw data) or
processed results from the interrogation results, could be
forwarded (such as by communication) to a remote location for
further evaluation and/or processing, or use, using communication
channel 180 or reader/writer 186 and medium 190. This data may be
transmitted by others as required to reach the remote location, or
re-transmitted to elsewhere as desired.
[0047] In a variation of the above, it is possible that each array
12 and its substrate 10 may be contained with a suitable housing.
Such a housing may include a closed chamber accessible through one
or more ports normally closed by septa, which carries the substrate
10. It will also be appreciated that an image of a target feature
location may include just a portion of that location, and that an
image set preferably, but not necessarily, includes all of the
droplets for that feature.
[0048] Modifications in the particular embodiments described above
are, of course, possible. For example, where a pattern of arrays is
desired, any of a variety of geometries may be constructed other
than the organized rows and columns of arrays 12 of FIG. 1. For
example, arrays 12 can be arranged in a series of curvilinear rows
across the substrate surface (for example, a series of concentric
circles or semi-circles of spots), and the like. Similarly, the
pattern of regions 16 may be varied from the organized rows and
columns of spots in FIG. 2 to include, for example, a series of
curvilinear rows across the substrate surface(for example, a series
of concentric circles or semi-circles of spots), and the like. Even
irregular arrangements of the arrays or the regions within them can
be used.
[0049] 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 mm, 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. However, larger substrates can be used, particularly when
such are cut after fabrication into smaller size substrates
carrying a smaller total number of arrays 12. Substrates of other
configurations and equivalent areas can be chosen. The
configuration of the array may be selected according to
manufacturing, handling, and use considerations.
[0050] 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; fused silica, silicon, plastics (for
example, polytetrafluoroethylene, polypropylene, polystyrene,
polycarbonate, and blends thereof, and the like); metals (for
example, gold, platinum, and the like).
[0051] The substrate surface onto which the polynucleotide
compositions or other moieties is deposited may be porous or
non-porous, 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),
[0052] Various further modifications to the particular embodiments
described above are, of course, possible. Accordingly, the present
invention is not limited to the particular embodiments described in
detail above.
* * * * *