U.S. patent application number 13/231430 was filed with the patent office on 2012-01-05 for microfabricated apparatus for cell based assays.
This patent application is currently assigned to GYROS Patent AB. Invention is credited to Per Andersson, Nicholas Thomas.
Application Number | 20120003682 13/231430 |
Document ID | / |
Family ID | 10830968 |
Filed Date | 2012-01-05 |
United States Patent
Application |
20120003682 |
Kind Code |
A1 |
Thomas; Nicholas ; et
al. |
January 5, 2012 |
MICROFABRICATED APPARATUS FOR CELL BASED ASSAYS
Abstract
Apparatus and methods are provided for performing cell growth
and cell based assays in a liquid medium. The apparatus comprises a
base plate supporting a plurality of micro-channel elements, each
micro-channel element comprising a cell growth chamber, an inlet
channel and an outlet channel, a cover plate positioned over the
base plate to define the chambers and connecting channels. Means
are incorporated in the cell growth chambers, for cell attachment
and cell growth. In particular, the invention provides a rotatable
disc microfabricated for performing cell growth and cell based
assays. The apparatus and method can be used for the growth of
cells and the detection and measurement of variety of biochemical
processes and products using non-invasive techniques, that is
techniques which do not compromise the integrity or viability of
cells.
Inventors: |
Thomas; Nicholas; (Radyr
Cardiff, GB) ; Andersson; Per; (Uppsala, SE) |
Assignee: |
GYROS Patent AB
Uppsala
SE
|
Family ID: |
10830968 |
Appl. No.: |
13/231430 |
Filed: |
September 13, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12236120 |
Sep 23, 2008 |
8030062 |
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13231430 |
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10650412 |
Aug 28, 2003 |
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12236120 |
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09673169 |
Nov 17, 2000 |
6632656 |
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PCT/GB99/00954 |
Mar 17, 1999 |
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10650412 |
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Current U.S.
Class: |
435/29 |
Current CPC
Class: |
B01L 3/5027 20130101;
B01L 3/502761 20130101; C12M 23/16 20130101; C12M 23/38 20130101;
C12M 25/16 20130101; B01L 2300/0877 20130101; B01L 3/502707
20130101; B01L 2400/0688 20130101; B01L 2300/087 20130101; B01L
2300/10 20130101; B01L 2300/0864 20130101; B01L 2200/10 20130101;
B01L 2400/0409 20130101; B01L 3/502753 20130101; B01L 2300/0806
20130101 |
Class at
Publication: |
435/29 |
International
Class: |
C12Q 1/02 20060101
C12Q001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 27, 1998 |
GB |
9808836.2 |
Claims
1.-19. (canceled)
20. A method for determining the effect of a test substance on cell
migration, which method comprises: a) providing an apparatus having
i) a base plate supporting a plurality of micro-channel elements,
each comprising a cell growth chamber, an inlet channel for
supplying liquid sample thereto and an outlet channel for removal
of liquid sample therefrom; ii) a cover plate positioned over said
base plate, said cover plate extending over said elements so as to
define said chambers and channels; and iii) barrier means in said
cell growth chambers for impeding the passage of cells in the cell
growth chamber; b) introducing said cells into said apparatus and
causing said cells to be transported to one side of the barrier
means in one or more cell growth chambers in said apparatus, c)
providing one or more samples of test substances whose effect on
cell migration is to be measured under conditions so as to cause
said cells to be exposed to said substances, and d) determining
migration of cells through said barrier in response to said
substance or substances.
21. The method according to claim 20, wherein said cell migration
is chemotaxis.
22. The method according to claim 21, wherein a chemoattractant is
placed on the other side of said barrier means.
23. The method according to claim 20, wherein said barrier means
comprise raised moulded structures disposed on the base portion of
the cell growth chamber to form pillars.
24. The method according to claim 23, wherein gaps between the
pillars are between 5 and 50 .mu.m.
25. The method according to claim 20, wherein at least some of the
micro-channel elements each comprise one or more assay chambers
connected in line between said cell growth chamber and said outlet
channel.
26. The method according to claim 20, wherein the apparatus
comprises a flow system for causing liquid flow through the
micro-channel elements.
27. The method according to claim 26, wherein the liquid flow is
controlled by centrifugal force.
28. The according to claim 20, wherein the base plate comprises a
rotatable disc which is microfabricated to provide a sample
introduction port located towards the center of the disc and
connected to an annular sample reservoir, and wherein the
micro-channel elements are radially dispersed on the disc with
their respective input channels connected to receive sample from
the reservoir.
29. The method according to claim 20, wherein the growth chambers
comprise localised regions modified to have surface properties
which promote cell growth.
30. The method according to claim 20, wherein weakly attached cells
in the growth chambers are removed by centrifugal force.
Description
[0001] The present invention relates to cell based assays. In
particular the invention relates to a microfabricated apparatus for
performing cell growth and cell based assays and to methods for
performing such assays.
[0002] The current focus in high throughput screening applications
towards the screening of increasing numbers of compounds is being
driven by the twin technologies of combinatorial chemistry and
genomics, in order to produce new potential drug targets and novel
candidate drugs as potential therapeutic compounds. The primary
screening process has been addressed by the development of high
throughput screening assay processes and assay miniaturisation
utilising the microtitre well plate format with 384, 864, 1536 or
greater miniaturised wells. Miniaturised assays are capable of
allowing throughput levels of over 100,000 tests/day in primary
screening. At this level of throughput, a primary screen might be
expected to yield 100-1000 `hits` per day. Each of these putative
drugs is required to undergo further refined screening and testing
in a variety of assays in order to investigate the biological
compatibility of the compound. Such assays include bioavailability,
metabolism and toxicology, and they are carried out predominantly
using cultured cell lines. In comparison with assays used in the
primary screening process, secondary screening assays have a much
higher level of complexity and more stringent requirements, both in
the mechanics of the assay and in the information generated. There
is a requirement in the art for secondary screening assay
methodologies which are capable of handling both the increasing
rate of putative drug lead generation and the generation of
biological data concerning the drug candidate. In addition,
development of assays yielding higher information content have the
potential to increase the level of characterisation of a lead drug
during the screening phase of drug development.
[0003] Microfabricated devices have been described previously which
are suitable for use in miniaturized biological analyses. For
example, WO 96/15450 discloses a device which comprises an etched
glass structure with a collection of chambers connected by a
micro-channel and enclosed by a glass cover plate. Devices have
been described by Wilding et al., for example in WO 93/22058, which
discloses a mesoscale device for amplifying DNA by PCR, the device
consisting of a number of chambers connected by a channel. WO
93/22055 and WO 93/22053 relate to devices for analysing a fluid
cell-containing sample comprising a mesoscale flow system with
entry port for capture and/or lysis of cells in biological fluids,
or containing a binding moiety for specifically binding an analyte,
where the analyte may be an intracellular component in a cell in a
sample, or a cell population in a sample. The above devices are
concerned with the measurement or detection of cells or cellular
analytes in cells introduced into the device immediately prior to
analysis. They are not described for use in cell culture or growth,
nor for use in the study of cellular responses to agents under
test. Moreover, they do not describe or permit the use of adherent
cultured cells.
[0004] There is a requirement for a device capable of providing an
environment which supports the long term survival of cultured
cells, coupled with means to utilise cells cultured within the
device for secondary drug screening or other studies.
[0005] In one aspect, the present invention provides apparatus
microfabricated for performing cell growth and cell based assays in
a liquid medium, said apparatus comprising:
a) a base plate supporting a plurality of micro-channel elements,
each comprising a cell growth chamber, an inlet channel for
supplying liquid sample thereto and an outlet channel for removal
of liquid sample therefrom; b) a cover plate positioned over said
base plate said cover plate extending over said elements so as to
define said chambers and connecting channels; said cover plate
being supplied with holes to provide access to said channels; and
c) means, incorporated in said cell growth chambers, for cell
attachment and cell growth.
[0006] In a second aspect of the invention there is provided a
method for studying the effect of a test substance on a cellular
activity or physical parameter by the use of the apparatus as
defined, which method comprises:
a) providing a suspension of cells in a fluid medium; b)
introducing said cells into said apparatus and causing said cells
to be transported to one or more cell growth chambers in said
apparatus; c) providing one or more samples of test substances
whose effect upon the cells is to be measured under conditions so
as to cause said cells to be exposed to said substances; d)
determining the effect of the test substances on said cells by
means of optical detection.
[0007] Preferably the method for studying the effect of a test
substance includes the step of culturing cells adhering to a
surface within the apparatus prior to the introduction of the test
substances. Preferably there are provided following step c) one or
more assay reagents and dispersing the reagents to one or more
reaction chambers in the apparatus.
[0008] In a further aspect of the present invention there is
provided a method for measuring a cellular analyte by the use of
the apparatus as defined, which method comprises:
a) providing a suspension of cells containing an analyte to be
measured in a fluid medium; b) introducing cells into the apparatus
and causing the cells to be transported to one or more cell growth
chambers in the apparatus; c) allowing cells to grow; d) providing
one or more assay reagents and dispersing the reagents to one or
more chambers in the apparatus; e) measuring the cellular analyte
by optical means.
[0009] In order that the invention may be better understood,
several embodiments will now be described by way of example only
and with reference to the accompanying drawings in which:
[0010] FIG. 1a is a diagrammatic representation in plan of an
individual micro-channel element of the microfabricated apparatus
for performing cell growth and cell based assays;
[0011] FIG. 1b is a sectional view of a microfabricated disc
including a plurality of assay elements for performing cell growth
and cell based assays according to the present invention;
[0012] FIG. 2 represents an alternative configuration of an
individual assay element of the microfabricated apparatus for use
with cells growing on the surface of microcarrier beads; and
[0013] FIG. 3 represents a further configuration of an individual
assay element of the microfabricated apparatus in which means are
provided for preventing or impeding the passage of cells in the
cell growth chamber.
[0014] Referring to FIG. 1b, the apparatus of the present invention
comprises a rotatable disc (18) microfabricated to provide a sample
introduction port (not shown) located towards the centre of the
disc and connected to an annular sample reservoir (9) which in turn
is connected to a plurality of radially dispersed micro-channel
assay elements (6) each of said micro-channel elements comprising a
cell growth chamber, a sample inlet channel and an outlet channel
for removal of liquid therefrom and a cover plate positioned onto
said disc so as to define closed chambers and connecting channels.
Each micro-channel element is connected at one end to the central
sample reservoir (9) and at the opposing end to a common waste
channel (10).
[0015] Each of the radially-dispersed micro-channel elements (6) of
the microfabricated apparatus (shown in FIG. 1a) comprises a sample
inlet channel (1) connected at its left hand-end end to the
reservoir (9), a cell growth chamber (2) for performing cell growth
and connected through a channel (4) to an assay chamber (3) and an
outlet channel (5) connected at its right-hand end to the waste
channel (10).
[0016] In an alternative format of the present invention as shown
in FIG. 2, the micro-channel elements (6) are modified to permit
the use of the apparatus with cells growing on the surface of
microcarrier beads (17). Thus, each micro-channel element (6)
comprises a sample inlet channel (8) connected at its left-hand end
to the sample reservoir (9), a cell growth chamber (7) connecting
through a channel (16) to an assay chamber (11), and an outlet
channel (12) leading to the common waste channel (10).
[0017] With reference to FIG. 3, in a further embodiment of the
apparatus, the cell growth chamber (2) may be provided with raised
moulded structures disposed on the base portion of the cell growth
chamber to form pillars (15), such that they form a barrier to the
flow or passage of cells arriving in the cell growth chamber (2)
through the inlet channel (1), while allowing the passage of
liquid. These structures are of dimensions chosen to provide gaps
between the structures which are too narrow to allow passage of
cells carried as a suspension in liquid moving in the device, but
which are sufficiently large to allow cells growing on the surface
of the cell growth chamber (14) to migrate through the barrier by
extension of cell processes between the barrier and subsequent
cytokinesis. Suitable dimensions for the gaps between the raised
pillars (15) formed in the cell growth chambers are between 5 and
50 .mu.m, depending upon the cell type and cell size selected for
capture.
[0018] Preferably, each micro-channel element (6) shown in FIG. 3
additionally includes one or more assay chambers for performing
assays involving cellular constituents and being connected in line
between said cell growth chamber (2) and said outlet channel
(5).
[0019] Suitably the disc (18) is of a one- or two-piece moulded
construction and is formed of an optionally transparent plastic or
polymeric material by means of separate mouldings which are
assembled together to provide a closed structure with openings at
defined positions to allow loading of the device with liquids and
removal of waste liquids. In the simplest form, the device is
produced as two complementary parts, one or each carrying moulded
structures which, when affixed together, form a series of
interconnected micro-channel elements within the body of a solid
disc. Alternatively the micro-channel elements may be formed by
micro-machining methods in which the micro-channels and chambers
forming the micro-channel elements are micro-machined into the
surface of a disc, and a cover plate, for example a plastic film,
is adhered to the surface so as to enclose the channels and
chambers.
[0020] To provide cultured cells with means for obtaining oxygen
for metabolism and to permit use of CO.sub.2-buffered media, one or
more components of the device may be constructed from a gas
permeable plastic, film, polymer, or membrane. Suitably, the gas
permeable plastic, film, polymer, or membrane is formed from
silicone polymers, such as polydimethylsiloxane, or from
polyurethane, polytetrafluoroethylene or other gas permeable
plastic materials. In addition, means (not shown) are preferably
provided for sealing the openings in the closed structure to
prevent evaporation of liquid during use, whereby such means seal
the openings without interfering with gas exchange to the cell
growth medium. Sealing can be accomplished by use of a further
layer of gas permeable material across the whole device, or by use
of a non-permeable material applied locally to the openings only,
leaving the remainder of the gas permeable material exposed to the
local atmosphere.
[0021] Suitable plastic or polymeric materials for forming the cell
growth chamber and micro-channels are preferably selected to have
hydrophobic properties, where the surface of the plastic or polymer
can be additionally selectively modified by chemical or physical
means to alter the surface properties to confer a desired property,
for example, compatibility with cell growth, cell attachment and
the attachment of biomolecules by covalent or non-covalent means.
Preferred plastics are selected from polystyrene and
polycarbonate.
[0022] Alternatively, the cell growth chamber and micro-channels
may be constructed from plastic or polymeric materials which are
selected to have hydrophilic properties. The surface of the plastic
or polymer can be additionally selectively modified by chemical or
physical means to alter the surface properties so as to produce
localised regions of hydrophobicity within the chambers and/or
microchannels to confer a desired property. By this means, for
example, hydrophobic barriers or valves may be provided to control
liquid flow within the apparatus. Preferred plastics are selected
from polymers with a charged surface, suitably chemically or
ion-plasma treated polystyrene, polycarbonate or other rigid
transparent polymers.
[0023] The micro-channel elements (6) are dispersed radially around
the disc (18) and connected to a common centre port. The channels
1, 4, 5, 8, 12, and 16 are of a dimension compatible with movement
of cells along the channels. Suitably, the channels and chambers
may be of any cross-sectional shape, such as square, rectangular,
circular, trapezoid and triangular. Suitably, the cell growth
chamber (2) is sized to give a floor area between 100 .mu.m.sup.2
and 1,000,000 .mu.m.sup.2, preferably between 1000 .mu.m.sup.2 and
1,000,000 .mu.m.sup.2 and most preferably between 10,000
.mu.m.sup.2 and 1,000,000 .mu.m.sup.2. The plastic or polymer
surface of the cell growth chamber may be selectively treated or
modified to permit cell attachment and/or growth. Treatment
preferably involves exposure to intense UV light to modify the
polymer surface or alternatively the use of high voltage plasma
discharge using known techniques (see Amstein, C. F. and Hartmann,
P. A., J.Clin.Microbiol., 2, 1, 46-54 (1975)) to create a
negatively charged surface suitable for cell growth and attachment
and (if required) for assay purposes. Cell attachment may be
further improved by the application of additional coatings to the
surface of the cell growth chamber, eg. polylysine, collagen,
fibronectin.
[0024] As already mentioned, in the preferred aspect of the
invention, each of the micro-channel elements (6) is further
provided with an assay chamber (3) which is located in line between
the cell growth chamber (2) and the outlet channel (5), for
performing assays involving cellular constituents. The assay
chamber is sized proportionally to the volume of the cell growth
chamber (2) to allow collection and/or capture of soluble analytes
which may be derived from the cultured cells under study. Suitably,
the volume of the assay chamber (3) is between twice and one tenth
of the volume of the cell growth chamber (2). Advantageously, the
channel (4) which connects the cell growth chamber and the assay
chamber is characterised by having hydrophobic walls and a
cross-sectional area which is smaller than the channel (1) upstream
of the cell growth chamber. Suitably, channel (4) has a
cross-sectional area of between 0.99 and 0.01 times that of the
inlet channel (1). Suitably, the outlet channel (5) is
characterised by having hydrophobic walls and a cross-sectional
area of between 0.99 and 0.01 times that of channel (4). In this
way, liquid flow in the micro-channel elements can be controlled by
application of a defined centrifugal force to cause the liquid to
flow in a channel of a defined cross-sectional area, wherein the
same force is insufficient to cause the liquid to flow in further
linked channels of lesser cross-sectional area, this having the
effect of stopping the liquid flow at a desired position in the
micro-channel element.
[0025] In an alternative means of controlling liquid flow, channel
(1) and channel (4) are constructed with the same cross-sectional
area, but the surface of each of the channels may be selectively
modified by chemical or physical means to confer a different degree
of hydrophobicity on that channel. For example, channel (4)
downstream of the cell growth chamber (2) may be treated to have a
higher hydrophobicity than the channel (1) upstream of the cell
growth chamber. By this means, application of a defined force to
liquid in channel (1), sufficient to cause liquid to move down this
channel will be insufficient to cause that liquid to enter the
second channel (4) of higher hydrophobicity, this having the effect
of stopping the liquid flow at a desired position in the
micro-channel element. Suitable means for selectively modifying the
hydrophobicity of the surface of the channels include exposure of
defined areas to ionizing or electromagnetic radiation or ion
plasma through a mask, or by application of a hydrophobic material
or ink by screen printing or other means of localized
application.
[0026] The means of controlling liquid flow within the apparatus as
described above may be used alone or in combination as required, in
order to confer the desired control of liquid flow in connected
chambers and channels within the micro-channel element. If used in
combination, the methods may be used sequentially, for example
where a change in cross-sectional area is followed by a change in
hydrophobicity, forming two sequential points of liquid flow
control. Alternatively, the methods may be used coincidentally, in
which a change in cross-sectional area of a channel is accompanied
by a change in hydrophobicity of that channel, the combination
being used to confer a degree of control over liquid flow not
attainable using a single means.
[0027] The inner surface of the assay chamber may be coated with
one or more ligands capable of specifically binding an analyte of
interest by covalently or non-covalently linking the ligand to the
surface. Examples of ligands suitable for the purpose include:
biotin, streptavidin, protein A, antibodies, lectins, hormone
receptors, nucleic acid probes, DNA binding proteins and the
like.
[0028] The apparatus and method can be used for the growth of cells
and the detection and measurement of cellular activity, cellular
parameters and biochemical processes, for example cellular
metabolism, cell viability, reporter gene expression, using
non-invasive techniques, that is techniques which do not compromise
the integrity or viability of cells. Alternatively, the apparatus
may be used in the detection and measurement of cell-derived
products, which have been released or otherwise excreted from
cells, such as peptide hormones, second messengers, etc. By use of
the apparatus shown in FIG. 3, the apparatus permits studies of
cell migration in response to chemical or physical stimuli, for
example chemotaxis, wherein a chemoattractant substance is placed
on one side of a barrier and cells placed on the opposite side of
the barrier are observed to penetrate the barrier in moving toward
the chemoattractant.
[0029] The invention may be used with any cell type that can be
cultured on standard tissue culture plastic-ware. Such cell types
include all normal and transformed cells derived from any
recognised source with respect to species (eg. human, rodent,
simian), tissue source (eg. brain, liver, lung, heart, kidney skin,
muscle) and cell type (eg. epithelial, endothelial). In addition,
cells which have been transfected with recombinant genes may also
be cultured using the invention. There are established protocols
available for the culture of diverse cell types. (See for example,
Freshney, R. I., Culture of Animal Cells: A Manual of Basic
Technique, 2.sup.nd Edition, Alan R.Liss Inc. 1987). Such protocols
may require the use of specialised coatings and selective media to
enable cell growth and the expression of specialist cellular
functions. None of such protocols is precluded from use with the
apparatus of this invention.
[0030] The scale of the device will to a certain extent be dictated
by its use, that is the device will be of a size which is
compatible with use with eukaryotic cells. This will impose a lower
limit on any channel designed to allow movement of cells and will
determine the size of cell containment or growth areas according to
the number of cells present in each assay. An average mammalian
cell growing as an adherent culture has an area of .about.300
.mu.m.sup.2; non-adherent cells and non-attached adherent cells
have a spherical diameter of .about.10 .mu.m. Consequently channels
for movement of cells within the device are likely to have
dimensions of the order of 20-30 .mu.m or greater. Sizes of cell
holding areas will depend on the number of cells required to carry
out an assay (the number being determined both by sensitivity and
statistical requirements). It is envisaged that a typical assay
would require a minimum of 500-1000 cells which for adherent cells
would require structures of 150,000-300,000 .mu.m.sup.2, i.e.
circular `wells` of .about.400-600 .mu.m diameter.
[0031] The configuration of the micro-channels in the present
invention is preferably chosen to allow simultaneous seeding of the
cell growth chamber by application of a suspension of cells in a
fluid medium to the sample reservoir by means of the sample inlet
port, followed by rotation of the disc (18) by suitable means at a
speed sufficient to cause movement of the cell suspension outward
towards the periphery of the disc by centrifugal force.
[0032] The movement of liquid distributes the cell suspension along
each of the inlet micro-channels (1, 8) towards the cell growth
chambers (2, 7). The rotation speed of the disc is chosen provide
sufficient centrifugal force to allow liquid to flow to fill the
cell growth chamber (2, 7), but with insufficient force for liquid
to enter the restricted channel (4, 16) of smaller diameter on the
opposing side of the cell growth chamber.
[0033] Once rotation has stopped, cells in the suspension can
settle under gravity onto the bottom of the cell growth chamber (2,
7) and attach to the treated surface if present. Cells which remain
in the channel are unable to attach to the untreated hydrophobic
surface and will remain in suspension. Therefore, following an
appropriate period of time, chosen to allow cell attachment to take
place, the device may be rotated at a higher speed than previously,
such that all liquid and unattached cells is caused to move towards
the periphery of the disc into the waste channel (10) disposed
around the edge of disc. Following clearance of channels of
unattached cells, rotation is slowed to the same speed initially
used to fill the micro-channel elements and fresh cell culture
media is applied to the sample reservoir. By rotation of the disc
once more, the cell culture media flows under centrifugal force to
fill the micro-channels and the cell growth chambers as previously
described. This action leaves the attached cells seeded on the
surface of the cell growth chambers covered in fresh culture media
suitable for cell growth and for cell based assays.
[0034] In the apparatus of FIG. 2, the beads (17) provide a large
surface area for cell attachment and growth in a relatively small
volume of liquid. In the device described herein, the beads (17)
perform two functions; firstly they provide a surface for the
attachment and growth of cells, so removing the need to provide a
cell-growth compatible surface within the disc allowing a wider
range of materials to be used for construction, and secondly they
provide a larger physical carrier for cells which allows channels
within the device to be easily designed to prevent access of cell.
In the preferred embodiment, each element comprises a cell growth
chamber (2, 7), an analysis chamber (3, 11), and a waste chamber
(10) which are arranged radially about the centre of the disc and
connected to a common port in the centre of the disc.
[0035] Following the addition of cell samples to the apparatus,
their attachment and subsequent cell growth, reagents and samples
for assay may be introduced into the sample reservoir (9) through
the sample inlet port. Reagents to be supplied to all micro-channel
elements may be introduced as described hereinbefore for seeding
with cells, that is by applying a solution containing reagents to
the central port and rotating the disc so as to cause distribution
of the reagent to all micro-channels, cell growth chambers and
assay chambers. The application of specific samples to specific
wells may be achieved by pipetting small volumes of liquid as
discrete drops into the central well directly adjacent to the
opening of the inlet channel leading to the cell growth chamber
which is to receive the sample. This may be achieved, for example,
by the use of a piezo-electric dispensing device (not shown),
whereby dispensing of droplets of liquid from the device is
synchronised with the speed of rotation of the disc (18) such that,
at an appropriate combination of dispensing drop frequency and
rotation speed of the disc, individual droplets of liquid can be
caused to impinge on the surface of the disc and can be caused to
be transported by centrifugal force into an adjacent inlet channel
(1, 8) and to mix with liquid present in the cell growth chamber
(2, 7).
[0036] Alternatively liquids may be pipetted as discrete drops onto
the hydrophobic surface of a stationary disc (18), rotation of the
disc being used to move these drops of liquid into the appropriate
inlet channel and so to the cell growth chamber. By these means,
all reagents and samples may be provided to the cell chamber in the
desired order and proportions to perform the assay.
[0037] Once the liquid manipulations of the assay have been
performed it is necessary to perform a detection procedure to
measure the result of the assay, typically by measuring the signal
emitted by a fluorescent, chemiluminescent or other labelling
moiety. The device as shown in FIG. 1b is configured to allow two
means of detection of the assay signal. Firstly, the assay signal
may be measured in-situ in the cell growth chamber. Such a signal
would be typified by the measurement of the product of a reporter
gene within the cells, e.g. fluorescence from GFP.
[0038] Alternatively, it may be desirable to measure cell-derived
products or analytes, for example by immunochemical or other
specific binding assay methods, in the absence of cells cultured in
the apparatus, so as to avoid interference in measurement. In this
case, the apparatus is provided with a second chamber, ie. the
assay chamber (3, 11) disposed closer to the periphery of the disc
and connected to the cell growth chamber (2, 7). The assay chamber
is connected to the peripheral waste channel (10) by a narrow
channel (5, 12), this channel having a smaller diameter than that
(4, 16) connecting the assay chamber to the cell growth chamber.
The differential in diameters between chambers allows, under
controlled conditions of rotation and centrifugal force, as
discussed above, liquid to be moved from the cell growth chamber to
the assay chamber. For example, by this process, an analyte is
moved from the cell growth chamber into the assay chamber where the
analyte is subject to affinity capture by a ligand attached to the
wall of the assay chamber. This process therefore provides a means
of moving a cell-derived analyte, which has been released or
otherwise excreted from cells, away from the cellular environment,
immobilising the analyte within the assay chamber by means of a
specific binding partner for binding to the analyte, and allowing
subsequent additions of reagents and processing to permit the
detection of the analyte.
[0039] Optionally, at least one of the reagents for use in an assay
method utilising the apparatus may be labelled with a detectable
label by covalent or non-covalent attachment. Suitable detectable
labels may be selected from fluorescent labels, chemi-luminescent
labels, bio-luminescent labels, enzyme labels and radioactive
labels. Suitable fluorescent labels for tagging reagents according
to the method of the invention may be selected from the general
categories of fluorescent dyes, including, but not limited to,
fluoresceins, rhodamines, cyanine dyes, coumarins, and the BODIPY
groups of fluorescent dyes. Examples of bioluminescent detectable
labels are to be found in the fluorescent reporter proteins, such a
Green Fluorescent Protein (GFP) and aequorin. Alternative labels
for providing a detectable signal can be fluorescence energy
transfer labels.
[0040] Once the assay has been completed, measurement of the signal
may be achieved by means appropriate to the labelling molecule or
moiety used in the assay and is typically by optical means. For
example, luminescence emitted from cells or from a fluorescent
labelled assay reagent may be detected in the microfabricated
apparatus by the use of imaging apparatus incorporating a CCD
camera, or by the use of a fluorimeter. Detection of emitted
fluorescence may be achieved through the body of the disc (18)
where the disc is wholly constructed of a transparent material or
alternatively through windows of transparent material which have
been fabricated into the body of the disc.
[0041] As an alternative to non-radioactive detection, the
apparatus of the present invention may be used in conjunction with
radioactive detection utilising the scintillation proximity
technique. For example, scintillant-containing beads may be
introduced into the apparatus. Alternatively the microfabricated
apparatus of the invention may have incorporated a scintillant
containing layer into or onto an interior surface of the cell
growth chamber (2, 7) and/or the assay chamber (3, 11). The region
of the apparatus containing the scintillant beads or scintillant
surface is preferably optically transparent so as to enable the
material to transmit light at a given wavelength with optimum
efficiency. The scintillant-containing region can be composed of
any transparent material containing scintillant, eg. a scintillant
glass based on lanthanide metal-containing compounds, or a plastic
material such as polystyrene or polyvinyltoluene, into which is
incorporated the scintillant substance.
[0042] Suitable scintillant substances can include aromatic
hydrocarbons such as p-terphenyl, p-quaterphenyl and their
derivatives, and derivatives of oxazoles and 1,3,4-oxadiazoles, for
example, 2-(4-t-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole and
2,5-diphenyloxazole. A wavelength shifter such as
1,4-bis(5-phenyl-2-oxazolyl)benzene, or 9,10-diphenylanthracene,
may also be included.
[0043] A binding moiety such as one member of a specific binding
pair may be immobilised onto the surface of the bead or scintillant
layer so as to specifically bind with an analyte which may be
derived from cells used in the assay process. Suitable specific
binding pair members with which the invention is useful include
biotin, streptavidin, protein A, antibodies, lectins, hormone
receptors, nucleic acid probes, DNA binding proteins and the like.
It is to be understood that either member of the specific binding
pair may be attached and immobilised for binding to a complementary
member of the specific binding pair.
[0044] Typical radioistopes that may be used to label the assay
reagent include those commonly used in biochemistry such as
[.sup.3H], [.sup.125I], [.sup.36S] and [.sup.33P] but does not
preclude the use of other isotopes. Detection methodologies based
on scintillation proximity are well known (see for example U.S.
Pat. No. 4,568,649, Bertoglio-Matte, J.). Detection may utilise a
number of modalities to be combined to allow all assays to be
measured simultaneously or in rapid succession. Alternatively an
appropriate imaging format may provide suitable detection means for
both radioactive and non-radioactive assays utilising the
apparatus.
[0045] In some uses, some assay areas will be redundant; that is,
not all elements of the apparatus will be used every time. It is
envisaged that the user will decide what type of assays it is
required to perform and then select appropriate control means for
directing liquid flow within the apparatus. Consequently, such
structures will be compatible with a range of assay procedures and
protocols which require different complexities of fluid movement.
For example, detection of a GFP linked reporter gene will require a
simple well structure to allow measurement of fluorescence. In
contrast, measurement of an analyte secreted from cells, for
example the measurement of a cytokine by immunoassay, or
measurement of cellular mRNA following lysis, will require a more
complicated structure to separate the cells from the secreted
analyte prior to the analysis of that analyte
[0046] The invention is further illustrated by reference to the
following examples.
EXAMPLE 1
[0047] A stock culture of HeLa cells was grown in Dulbecco's
Modified Eagles Medium (DMEM) supplemented with 10% calf serum and
L-glutamine in a plastic flask using standard tissue culture
conditions. Cells were harvested by trypsinisation and the
resulting suspension concentrated by centrifugation to give a cell
concentration of 10.sup.7 cells/ml. Aliquots of the cell suspension
(1 .mu.l) were applied to openings in the surface of a
microfabricated structure of the type shown in FIG. 1, produced by
injection moulding, with internal channels of depth 50 .mu.m and
width 100 .mu.m.
[0048] The cells suspension was moved along the inlet channels
within the disc to circular cell growth chambers of depth 50 .mu.m
and diameter 500 .mu.m and the cells allowed to attach and grow.
Following incubation for 48 hours in a tissue culture incubator
(37.degree. C./95% RH) the cells were examined for cell density,
morphology and viability. Visible examinations by phase contrast
microscopy showed cell populations growing in microstructures to
have the same density and morphology as control cultures grown from
the same parent stock and maintained in standard tissue culture
plasticware. Cells were subsequently tested for viability using a
commercial test kit (LIVE/DEAD Viability Kit, Molecular Probes,
Oregon, L-3224) by flushing growth medium from the cells within the
device, washing the cells with a phosphate buffered saline solution
(PBS) and introducing a solution of the fluorescent assay reagents
into the cell growth chambers. Subsequent examination by
fluorescent microscopy showed that cells growing in microstructures
had maintained a cell viability of >95%, comparable with control
cells grown under standard tissue culture conditions.
EXAMPLE 2
[0049] A microfabricated plastic disc of the type shown in FIG. 1,
produced by injection moulding which contained a number of radial
internal channels of depth 50 .mu.m and width 100 .mu.m was
selectively surface modified by exposure to a 500 W UV lamp at a
distance of 20 cm for 30 minutes through a metal mask such that UV
light impinged on the surface only on regions defined by the
mask.
[0050] A stock culture of HeLa cells was grown in Dulbecco's
Modified Eagles Medium (DMEM) supplemented with 10% calf serum and
L-glutamine in a plastic flask using standard tissue culture
conditions. Cells were harvested by trypsinisation and the
resulting suspension concentrated by centrifugation to give a cell
concentration of 10.sup.7 cells/ml. Aliquots of the cell suspension
(1 .mu.l) were applied to openings in the surface of the device and
cells moved along the channels by rotation about the disc axis
(1000 rpm for 30 seconds). Following incubation for 18 hours in a
tissue culture incubator (37.degree. C./95% RH) cells were examined
by phase contrast microscopy. Cells were found to be preferentially
growing in regions of the disc previously exposed to UV light,
cells in other regions were observed to be sparser and less well
attached. The disc was then rotated at 1000 rpm for 30 seconds and
cells re-examined. Following spinning cells in UV exposed areas
were observed to have remained attached to the plastic surface and
remained morphologically identical to control cells; in contrast
cells on non-exposed surfaces were totally removed by the
centrifugal force generated by the spinning disc.
EXAMPLE 3
[0051] HeLa cells grown and harvested as described above were
introduced into the device of Example 2 into micro channels which
contained moulded pillars of various dimensions dispersed in the
channels so as to act as barriers to cell movement in the channels.
A suspension of cell was introduced into the channels and the
structure incubated for 18 hours to allow the cells to settle and
grow. Subsequent examination revealed that in channels where the
gaps between pillars were 10.times.60 .mu.m or greater cells were
observed to have moved freely past the barriers. In contrast where
gaps between pillars were 10.times.20 .mu.m or less, cells were
prevented from passing the barrier when transported by liquid flow
in suspension. However on subsequent incubation and growth cells
were observed to migrate past such barriers by slow deformation.
Such barrier structures may prove useful for study of cell movement
or migration in response to chemical or physical stimuli.
EXAMPLE 4
[0052] HeLa cells transfected to yield stable expression of a
Calreticulin-GFP fusion protein were introduced into a moulded
apparatus of the type shown in FIG. 1, supporting channels of 100
.mu.m width and 100 .mu.m depth connected to circular chambers of
600 .mu.m and 1000 .mu.m diameter and 100 .mu.m depth. Cells were
incubated for 18 hours in a tissue culture incubator and examined
by confocal fluorescence microscopy. Cells grown in microfabricated
structures showed the same level of GFP expression as control cells
grown under conventional tissue culture conditions.
EXAMPLE 5
[0053] HeLa cells were grown and introduced into a microfabricated
disc as described in Example 1. Following incubation for 18 hours
growth medium was removed from cells and replaced with media
containing different concentrations of the membrane permeabilising
agent digitonin in the range 0-0.2 mg/ml (w/v) and cells incubated
in the presence of digitonin for 10 minutes. Thereafter the
viability of the cells was measured as described in Example 1.
Results were found to be equivalent to cells exposed to the same
dose range of digitonin in a microtitre plate based assay.
* * * * *