U.S. patent application number 11/568762 was filed with the patent office on 2008-10-30 for image locking system for dna micro-array synthesis.
This patent application is currently assigned to Wisconsin Alumni Research Foundation. Invention is credited to Francesco Cerrina, Chang-Han Kim, Mo-Huang Li.
Application Number | 20080266562 11/568762 |
Document ID | / |
Family ID | 35239488 |
Filed Date | 2008-10-30 |
United States Patent
Application |
20080266562 |
Kind Code |
A1 |
Cerrina; Francesco ; et
al. |
October 30, 2008 |
Image Locking System for Dna Micro-Array Synthesis
Abstract
An image locking system for DNA micro-array synthesis provides a
feedback system to stabilize or lock the image with respect to an
image capture device, such as a camera and/or microscope. The image
locking system includes the use of detection or reference marks.
When a shift in image position is detected, a correction signal is
sent to one of two mirrors, moving the image to correct for the
shift in image position. The system comprises a first light beam
directed towards a micromirror device that forms an alignment
pattern on a reaction cell and a second light beam directed towards
the micromirror device that forms a micro-array image on an active
surface of the reaction cell. A camera captures the alignment
pattern and an alignment mark. A computer calculates a correction
signal to realign the alignment pattern with the alignment mark
when movement is detected.
Inventors: |
Cerrina; Francesco;
(Madison, WI) ; Li; Mo-Huang; (Madison, WI)
; Kim; Chang-Han; (Madison, WI) |
Correspondence
Address: |
FOLEY & LARDNER LLP
150 EAST GILMAN STREET, P.O. BOX 1497
MADISON
WI
53701-1497
US
|
Assignee: |
Wisconsin Alumni Research
Foundation
Madison
WI
|
Family ID: |
35239488 |
Appl. No.: |
11/568762 |
Filed: |
March 25, 2005 |
PCT Filed: |
March 25, 2005 |
PCT NO: |
PCT/US05/10116 |
371 Date: |
August 22, 2007 |
Current U.S.
Class: |
356/401 |
Current CPC
Class: |
G02B 7/1827 20130101;
G02B 19/0095 20130101; B01J 2219/0054 20130101; G02B 17/008
20130101; G02B 19/0047 20130101; G02B 17/0615 20130101; B01J
2219/00722 20130101; B01J 2219/00612 20130101; B01J 2219/00608
20130101; B01J 2219/00439 20130101; G02B 26/0833 20130101; B01J
2219/00693 20130101; B01J 2219/00626 20130101; B01J 19/0046
20130101; G02B 19/0023 20130101 |
Class at
Publication: |
356/401 |
International
Class: |
G01B 11/00 20060101
G01B011/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 7, 2004 |
US |
10841847 |
Claims
1. An image locking system for use in DNA micro-array synthesis,
the system comprising: a reaction cell with an active surface on
which a micro-array may be formed; a micromirror device, the
micromirror device formed of an array of electronically addressable
micromirrors wherein each micromirror can be selectively tilted
between one of at least two positions whereby a first light beam
directed towards the micromirror device forms a micro-array image
on the active surface of the reaction cell; an alignment mark
located at the reaction cell; a second light beam that is directed
towards the micromirror device thereby forming an alignment pattern
on the reaction cell; a camera capturing an alignment image, the
alignment image comprising the alignment mark and the alignment
pattern reflected onto the reaction cell; a computer identifying a
change in the alignment image and calculating a correction signal
to remove the change from the alignment image; and at least one
actuator provided to adjust the alignment image in response to the
correction signal calculated by the computer.
2-14. (canceled)
15. A method of forming an image locking system for use in DNA
micro-array synthesis, the method comprising: projecting a first
light beam towards a micromirror device that forms an initial
alignment pattern; reflecting the initial alignment pattern along
an optical path and onto a reaction cell; capturing an initial
alignment image wherein the initial alignment image comprises an
alignment mark and the initial alignment pattern projected onto the
reaction cell; projecting the first light beam towards the
micromirror device that forms a current alignment pattern;
reflecting the current alignment pattern along the optical path and
onto the reaction cell; capturing a current alignment image wherein
the current alignment image comprises the alignment mark and the
current alignment pattern projected onto the reaction cell;
calculating the displacement between the initial alignment image
and the current alignment image; and sending a correction signal to
at least one actuator to remove the displacement between the
initial alignment image and the current alignment image.
16-29. (canceled)
30. A method of forming an image locking system for use in DNA
micro-array synthesis, the method comprising: projecting a first
light beam towards a micromirror device that forms an initial
alignment pattern; reflecting the initial alignment pattern along
an optical path and onto a reaction cell; capturing an initial
alignment pattern image of the initial alignment pattern projected
onto the reaction cell; projecting the first light beam towards a
micromirror device that forms a current alignment pattern;
reflecting the current alignment pattern along the optical path and
onto the reaction cell; capturing a current alignment pattern image
of the current alignment pattern projected onto the reaction cell;
calculating the displacement between the initial alignment pattern
image and the current alignment pattern image; and sending a
correction signal to at least one actuator to remove the
displacement between the initial alignment pattern image and the
current alignment pattern image.
31-46. (canceled)
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to the field of DNA
micro array and synthetic DNA strands manufacturing. More
particularly, the present invention relates to an image locking
system for DNA micro-array synthesis.
BACKGROUND OF THE INVENTION
[0002] Researchers believe that thousands of genes and their
products (i.e., RNA and proteins) in a given living organism
function in a complicated and orchestrated way. However,
traditional methods in molecular biology generally work on a "one
gene in one experiment" basis, which means that the throughput is
very limited and the "whole picture" of gene function is hard to
obtain. In the past several years, a new technology, called DNA
microarray, has attracted tremendous interests among biologists.
This technology attempts to monitor the whole genome on a single
chip so that researchers can have a better picture of the
interactions among thousands of genes simultaneously.
[0003] An array is an orderly arrangement of samples. It provides a
medium for matching known and unknown DNA samples based on
base-pairing rules and automating the process of identifying the
unknowns. An array experiment can make use of common assay systems,
such as microplates or standard blotting membranes, and can be
created by hand or make use of robotics to deposit the sample. In
general, arrays are described as macroarrays or microarrays, the
difference being the size of the sample spots. Macroarrays contain
sample spot sizes of about 300 microns or larger and can be easily
imaged by existing gel and blot scanners. The sample spot sizes in
microarray are typically less than 200 microns in diameter and
these arrays usually contains thousands of spots. Microarrays
require specialized robotics and imaging equipment that generally
are not commercially available as a complete system.
[0004] DNA microarray, or DNA chips, are fabricated by high-speed
robotics, generally on glass but sometimes on nylon substrates, for
which probes with known identity are used to determine
complementary binding, thus allowing massively parallel gene
expression and gene discovery studies. An experiment with a single
DNA chip can provide researchers information on thousands of genes
simultaneously--a dramatic increase in throughput.
[0005] In the process of manufacturing DNA micro array and
synthetic DNA strands, an image is repeatedly projected on the
substrate. While the substrate is not moved during processing, the
images need to be kept stable across different phases of exposure
that may last a total of 4-8 hours. During this time, the optical
system drifts from its reference state because, for instance, of
changes in the environment. It is not practical to try to
completely eliminate these drifts. As such, there is a need for a
feedback system to stabilize or lock the image used in the DNA
micro array and strands manufacturing.
SUMMARY OF THE INVENTION
[0006] In accordance with the present invention, an image locking
system for DNA micro-array synthesis provides a feedback system to
stabilize or lock the image with respect to an image capture
device, such as a camera and/or microscope. The image locking
system includes the use of detection or reference marks. When a
shift in image position is detected, a correction signal is sent to
one of two mirrors, moving the image to correct for the shift in
image position.
[0007] In an exemplary embodiment, the image locking system
includes a reaction cell with an active surface on which a
micro-array may be formed, a micromirror device, an alignment mark
located at the reaction cell, a second light beam that is directed
towards the micromirror device forming an alignment pattern on the
reaction cell, a camera that captures an alignment image that
comprises the alignment mark and the alignment pattern, a computer
that identifies a change in the alignment image and calculates a
correction signal to remove the change from the alignment image,
and at least one actuator provided to adjust the alignment image in
response to the correction signal calculated by the computer. The
micromirror device is formed of an array of electronically
addressable micromirrors wherein each micromirror can be
selectively tilted between one of at least two positions whereby a
first light beam directed towards the micromirror device forms a
micro-array image on the active surface of the reaction cell.
[0008] In an exemplary embodiment, a method of forming an image
locking system comprises projecting a first light beam towards a
micromirror device that forms an initial alignment pattern,
reflecting the initial alignment pattern along an optical path and
onto a reaction cell, capturing an initial alignment image wherein
the initial alignment image comprises an alignment mark and the
initial alignment pattern projected onto the reaction cell,
projecting the first light beam towards the micromirror device that
forms a current alignment pattern, reflecting the current alignment
pattern along the optical path and onto the reaction cell,
capturing a current alignment image wherein the current alignment
image comprises the alignment mark and the current alignment
pattern projected onto the reaction cell, calculating the
displacement between the initial alignment image and the current
alignment image, and sending a correction signal to at least one
actuator to remove the displacement between the initial alignment
image and the current alignment image.
[0009] In an alternative embodiment, the method of forming an image
locking system comprises projecting a first light beam towards a
micromirror device that forms an initial alignment pattern,
reflecting the initial alignment pattern along an optical path and
onto a reaction cell, capturing an initial alignment pattern image
of the initial alignment pattern projected onto the reaction cell,
projecting the first light beam towards a micromirror device that
forms a current alignment pattern, reflecting the current alignment
pattern along the optical path and onto the reaction cell,
capturing a current alignment pattern image of the current
alignment pattern projected onto the reaction cell, calculating the
displacement between the initial alignment pattern image and the
current alignment pattern image, and sending a correction signal to
at least one actuator to remove the displacement between the
initial alignment pattern image and the current alignment pattern
image.
[0010] Further objects, features and advantages of the invention
will be apparent from the following detailed description when taken
in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] In the drawings:
[0012] FIG. 1 is a diagrammatic representation of an illumination
and optical system of a maskless array synthesizer according to an
exemplary embodiment.
[0013] FIG. 2 is a schematic of an image locking system in
accordance with and exemplary embodiment.
[0014] FIG. 3 (a) is a diagrammatic representation of a reference
mark on a reaction cell.
[0015] FIG. 3 (b) is a diagrammatic representation of a projected
alignment pattern with the reference mark on a glass slide.
[0016] FIG. 3 (c) is a diagrammatic representation of locations of
alignment marks.
[0017] FIG. 4 (a) is a cross-section view of a reaction cell with
image locking in accordance with an exemplary embodiment.
[0018] FIG. 4 (b) is a diagrammatic representation of a captured
image to be processed in accordance with an exemplary
embodiment.
[0019] FIGS. 5 (a), (b), and (c) are captured images to be
processed.
[0020] FIG. 6 is a diagrammatic representation of an image
projected on a substrate where the image includes several
micro-mirrors.
[0021] FIG. 7 is a diagrammatic representation of an image
projected on a substrate wherein the image of the mask appears as a
dark line.
[0022] FIG. 8 is a diagrammatic representation of an exposure
scheme for performance verification.
[0023] FIGS. 9 (a) and (b) are diagrammatic representations of
radiochromic film images formed continuously without image
locking.
[0024] FIGS. 10 (a), (b), and (c) are diagrammatic representations
of radiochromic film images performed continuously with and without
image locking in accordance with an exemplary embodiment.
[0025] FIGS. 11 (a) and (b) are diagrammatic representations of a
virtual mask layout.
[0026] FIG. 12 is a diagrammatic representation of an image of a
microarray fabricated without using image locking.
[0027] FIGS. 13 (a)-(h) are diagrammatic representations of images
of a microarray fabricated without using image locking at 10 times
magnification.
[0028] FIGS. 14 (a)-(h) are diagrammatic representations of an
image of a microarray fabricated without using image locking at 50
times magnification.
[0029] FIG. 15 is a diagrammatic representation of an image of a
microarray fabricated using image locking.
[0030] FIGS. 16 (a)-(h) are diagrammatic representations of images
of a microarray fabricated using image locking in accordance with
an exemplary embodiment at 10 times magnification.
[0031] FIGS. 17 (a)-(h) are diagrammatic representations of an
image of a microarray fabricated using image locking in accordance
with an exemplary embodiment at 50 times magnification.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0032] FIG. 1 illustrates a schematic of an optical system 10 of a
gene synthesizer according to an exemplary embodiment. The system
10 includes a maskless array synthesizer 12 comprising a mercury
(Hg) arc lamp 14, a condenser 18, a digital micro-mirror device
(DMD) 20, and a microarray reaction cell 22. The digital
micromirror device (DMD) 20 may consist of a 1024.times.768 array
of 16 .mu.m wide micro-mirrors. Preferably, these mirrors are
individually addressable and can be used to create any given
pattern or image in a broad range of wavelengths. Each virtual mask
is generated in a bitmap format by a computer and is sent to the
DMD controller, which forms the image onto the DMD 20.
[0033] The maskless array synthesizer 12 can generate several .mu.m
of drift over several hours due to the thermal expansion of optics
parts. The optical path between the DMD 20 and DNA cell 22 is about
1 meter. Due to the thermal expansion caused by the temperature and
humidity fluctuation of surrounding environments and also due to
ultraviolet (UV) exposure, a slight change of position or rotation
of the primary spherical mirror and other optical parts may result.
This slight change may cause several .mu.m of drift of the
projected image. Since the space between each digital micromirror
is only 1 .mu.m, this image drift can cause the projected image to
be shifted to expose the UV light at the wrong oligonucleotide
spots, generating defects in oligonucleotides sequences and their
spatial distribution. An image locking system confines the image
shift within a certain range to minimize image drift.
[0034] FIG. 2 illustrates a diagram of an image locking system 28.
The image locking system 28 comprises a laser 42, a flat mirror 36,
a 1:1 ratio projection system 16, a camera 40, an x-actuator 48,
and a y-actuator 50. The 1:1 ratio projection system 16 comprises a
UV lamp 44, a digital light processor (DLP) or digital micromirror
device (DMD) 30, a concave mirror 32, a convex mirror 34, and a
reaction cell 38. The 1:1 ratio projection system 16 forms a UV
image of the virtual mask on the active surface of the glass
substrate mounted in a flow reaction cell 38 connected to a DNA
synthesizer. In an exemplary embodiment, the laser 42 is a He--Ne
laser with a wavelength of 632.8 nm (red light) and does not
disturb the photochemical reaction of oligonucleotide synthesis.
The He--Ne laser beam from the laser 42 is projected to a reaction
cell 38 using an "off" state (rotated -10.degree.) of micromirrors
without interrupting the current UV exposure system with UV light
from the UV lamp 44 which is projected to the reaction cell 38
using an "on" state (rotated 10.degree.) of micromirrors. The
He--Ne laser 42 is at the opposite side of the UV lamp 44 with
incident angle of -20.degree. into the DMD 30.
[0035] The system 28 can be a 0.08 numerical aperture reflective
imaging system based on a variation of the 1:1 Offner relay. Such
reflective optical systems are described in A. Offner, "New
Concepts in Projection Mask Aligners," Optical Engineering, Vol.
14, pp. 130-132 (1975). The DMD 30 can be a micromirror array
available from Texas Instruments, Inc. The reaction cell 38
includes a quartz block 47, a glass slide 49, a projected image 51,
and a reference mark 53. The UV lamp 44 can be a 1000W Hg Arc lamp
(e.g., Oriel 6287, 66021), which can provide a UV line at 365 nm
(or anywhere in a range of 350 to 450 nm). In an alternative
embodiment, the lamp 44 may be a visible wavelength lamp.
[0036] The laser 42 projects a laser beam onto flat mirror 36 which
reflects the beam onto DMD 30. DMD 30 has a two-dimensional array
of individual micromirrors which are responsive to the control
signals supplied to the DMD 30 to tilt in one of at least two
directions. A telecentric aperture may be placed in front of the
convex mirror 34.
[0037] The camera 40 is a charge coupled device (CCD) camera used
to capture an image of alignment marks. The captured image is
transferred to a computer 46 for image processing. When a
misalignment is detected, correction signals are generated by the
computer 46 and sent to actuators 48 and 50 as the feedback to
adjust the mirror 32, so that the correct alignment is
reestablished. In at least one alternative embodiment, three
electro-strictive actuators (instead of actuators 48 and 50) are
used to provide minimum incremental movement of 60 nm and control
the rotations and movement of the mirror 32. The displacement of
the projected image at the glass slide is highly sensitive to the
rotations and movement of the mirror 32.
[0038] FIG. 3(a) illustrates the alignment mark 53 patterned on the
quartz block 47 in the reaction cell 38. The quartz block 47
includes an outlet 55 and an inlet 57 through which fluid may flow
through the reaction cell 38. Such a reaction cell is described in
U.S. Pat. No. 6,375,903 entitled "Method and Apparatus for
Synthesis of Arrays of DNA Probes." A predefined micromirror
pattern shown in FIG. 3(b) is projected, being centered at the
alignment mark 53. In an exemplary embodiment, the projected image
51 is manually aligned at the beginning of synthesis, so that the
center of the projected image 51 is roughly overlapped with the
center of the alignment mark 53. The CCD camera 40 is used to
capture the image that is formed by a 20.times. (magnification)
microscope lens, which is focused at the middle between the
reference mark 53 and the projected image 51. An image processing
program in the computer 46 calculates the centers of the reference
mark 53 and the projected image 51, generating the amount and
direction of any displacement, and sending its correction signals
to the corresponding actuator(s) 48 and/or 50. The reference mark
53 is patterned on the surface of the quartz block 47 as shown in
FIG. 3(a). The relative position of the projected image 51 to the
reference mark 53 is shown at FIG. 3(c).
[0039] FIG. 4(a) illustrates a cross-sectional view of the reaction
cell 38. The projected image 51 is focused on an inner glass slide
surface 61 of the glass slide 49 where the oligonucleotides are
grown. The reference mark 53 and the projected image 51 are not at
the same focus plane. A microscope lens focuses at the middle plane
between the reference mark 53 and the projected image 51. As such,
the image captured by the camera 40 is blurred, as shown in FIG.
5(c). The gap between the glass slide surface 61 and quartz block
surface 65 of the quartz block 47 is 100 .mu.m. To locate the
center position of each pattern, an 2D optical pattern recognition
technique, which is based on correlation theory, is used.
Correlation analysis compares two signals (or images) in order to
determine the degree of similarity, where input signal is to be
searched for a reference signal. Each correlation gives a peak
value where the reference signal and input signal matches the best.
If the location of this value is different from the previous value,
it means that the image has been shifted, indicating the need of
correction.
[0040] In an exemplary embodiment, an image processing procedure
calculates the image displacement from the images captured by the
camera 40, by calculating the cross-correction signals between a
captured input image described with reference to FIG. 5(c), the
reference mark 53 of FIG. 5(a), and the projected image 51 of FIG.
5(b). The cross-correlation is a measure of the similarity between
two images, such as images from FIGS. 5(a) and 5(c) and such as
images from FIGS. 5(b) and 5(c). Mathematically, the
cross-correlation can be calculated as:
c gh ( X , Y ) = .intg. - .infin. .infin. .intg. - .infin. .infin.
g ( x , y ) h ( x + X , y + Y ) x y ##EQU00001##
or, using the Wiener-Khintchine Theorem, as:
c.sub.gh(X,Y)=IFFT(FFT2(g(X,Y))FFT2(rot90(h(X,Y))))
[0041] The new locations of the reference mark and the projected
image are marked by correlation peaks (i.e., the highest value of
c.sub.gh(X,Y)). Based on the new locations, correction signals are
computed and sent to the actuators to move the mirror. This
correction procedure continues until the synthesis is
completed.
[0042] In an exemplary embodiment, computer programs control the
actuators and generate the correction signals by image processing.
A log file of displacements can also be recorded and analyzed for
measuring actual displacement indirectly and its direction for
further refinement of the algorithm. Various mark shapes (e.g.,
crosses, chevrons, circles) can be used as the reference mark
53.
[0043] FIG. 6 illustrates an image 71 projected on a substrate
where the image includes several micro-mirrors 73, 75, 77, and 79
according to another exemplary embodiment. A reference mark 74 is
included on the substrate. In the field of microscope, the
micro-mirrors 73, 75, 77, and 79 appear as a bright image while the
reference mark 74 can be dark so that the image of the mask will
appear as a dark line 76 (FIG. 7). As such, overlap of the
micro-mirrors 73, 75, 77, and 79 and the reference mark 74 can be
observed. Image processing software can determine if the dark
shadows are centered on the micro-mirror and if not, apply a
correction.
[0044] Since each pixel is approximately 16 .mu.m in size, it is
necessary to keep the image locked to less than 200 nm. Since the
distance from the concave mirror 32 (FIG. 2) to the reaction cell
38 can be approximately 500 mm, the angle pointing accuracy is
0.4.times.10.sup.-6 radians. Since the diameter of the optics is
200 mm, a piezoelectric or similar system can be used to generate
the angular shift by applying a displacement of 80 nm. Typically, a
nanopositioner can control displacements of even 10 nm.
[0045] Other designs are possible, involving different schemes for
the detection of the displacements. The actuators 48 and 50 can be
used to effectively align the optics. In another exemplary
embodiment, diffractive marks can also be used, alleviating the
need for microscopes. Partially transmitting marks (half toned) can
be used for other schemes of detection.
[0046] FIGS. 8-10 illustrate the performance of an exemplary image
locking system. FIG. 8 illustrates image patterns for measuring
drift. In FIG. 8(a), a square shape reference frame 81 is exposed
at time equal to zero (t=0). In FIGS. 8(b), (c) and (d), each
adjacent pixel of the reference frame 81 is progressively exposed
every 10 min to create a line 83. If there is a drift, the gap
between the reference frame and the line 83 will change.
[0047] FIGS. 9(a) and (b) show the results of a projected image
shift as an image is projected without image locking. In one
experiment, the ambient temperature around the system was measured
to be 23.56.+-.1.degree. C. and the humidity around 23.2%. FIG.
9(b) shows a zigzag displacement is approximately half pixel's size
(.about.8 .mu.m) for 490 minutes exposure. Such a shift can
increase to about 50 .mu.m for 24 hour's continuous exposure.
[0048] FIGS. 10(a), (b), and (c) show the results of exposing
radiachromic film at room temperature for 200 minutes (pixels
1-20), and increasing the environmental temperature by 5.degree. C.
for 120 minutes (pixels 21-32). Then, the environmental temperature
is reduced back to room temperature for 150 minutes (pixels 33-48).
The humidity variation is 11.7% to 16.3% as the temperature change.
FIG. 10(a) illustrates the experimental results showing image drift
without image locking. However, in FIGS. 10(b) and (c) with image
locking, the image is stable with drift in each direction smaller
than 1 .mu.m.
[0049] FIGS. 11(a) and (b) show an exemplary virtual mask layout
used to verify the image locking performance. FIG. 11(a) shows the
entire mask (1024.times.768) and FIG. 11(b) shows one of the
sections of the mask that expands to the entire chip. From the
upper left corner to the lower right corner, the features are
composed of single pixel, 3.times.3, 5.times.5 (with interim
mirrors off), 1:4 ratio, 5.times.5 (all pixels on), 3.times.3 (of
9.times.9 mirrors), 5.times.5 (of 3.times.3 mirrors), 9:36
ratio.
[0050] FIG. 12 illustrates a fluorescence image with the
synthesized oligomers (25mer in length) using the virtual mask
layout described with reference to FIG. 11, hybridized with their
complementary sequences (probes) that has cy3 cynano-nucleotide at
its end. The chip is scanned in 2 .mu.m resolution using an applied
precision microarray scanner. The target oligomers have an
additional 5Ts as a linker on the substrate glass for efficient
hybridization.
[0051] The small features are not visible in FIG. 12 because they
have extremely low fluorescence signal intensity due to the lack of
exposure, caused by the image drifting over time. Larger features
have a relatively bigger overlapping area of exposure and those
areas have target oligonucleotides to be hybridized even though the
feature shape is distorted. However, small ones such as in the
upper row in FIG. 12 will have progressively smaller amount of
exposure as the synthesis advances, resulting in very poor
synthesis.
[0052] FIGS. 13 and 14 show the images of the same features as in
FIG. 12, captured by a Nikon Fluorescence Microscope using
10.times. and 50.times. lens respectively. In these Figures, the
hybridization signal intensities are not comparable to each other
because their images are scaled to be seen so that the shapes,
directions and amount of the drift can be brought out. Their actual
intensity of smaller features are approximately 10,000-fold lower
than the bigger ones. The single pixel that doesn't have any
adjacent pixels is not detectable due to its extremely low signal
and is not shown. In 100 cycles of synthesis, 5 to 6 pixels'
displacement occurred in the particular synthesis even though there
is no enforced environment change. FIG. 13(f) shows the
directionality of the drift. Only horizontal features are left,
indicating that there is some dominant directions of drift. FIG. 14
shows more magnified images of those shown in FIG. 13 by using a
50.times. lens instead of a 10.times. lens.
[0053] FIG. 15 is the scanned image of the DNA chip that was
fabricated under the same conditions as the chip in FIG. 12
(without image locking) but where the image locking system is
engaged. All the features in the mask layout are visible, keeping
their shape (square micromirror shape), even the single pixel. The
synthesis images also have maximum hybridization signal
intensities.
[0054] FIGS. 16 and 17 show fluorescence microscope capture images
using 10.times. and 50.times. respectively. The lanes and the posts
of the micromirros are clearly seen, indicating the firm image
locking.
[0055] It should be understood that the invention is not limited to
the embodiments set forth herein as illustrative, but embraces all
such forms thereof as come within the scope of the following
claims.
* * * * *