U.S. patent application number 14/247779 was filed with the patent office on 2015-10-08 for serial arrays of suspended microchannel resonators.
The applicant listed for this patent is Massachusetts Institute of Technology. Invention is credited to Nathan Cermak, Francisco Feijo Delgado, Scott Manalis, Selim Olcum.
Application Number | 20150285784 14/247779 |
Document ID | / |
Family ID | 54063475 |
Filed Date | 2015-10-08 |
United States Patent
Application |
20150285784 |
Kind Code |
A1 |
Delgado; Francisco Feijo ;
et al. |
October 8, 2015 |
Serial Arrays of Suspended Microchannel Resonators
Abstract
Serial suspended microchannel resonator sensor array. The array
includes a plurality of resonator cantilevers in fluid
communication with one another and a plurality of delay channels in
fluid communication with, and disposed between, the resonator
cantilevers. An object introduced into the array will flow in one
direction and be measured by each of the cantilevers in turn after
a selected delay in the delay channels.
Inventors: |
Delgado; Francisco Feijo;
(Boston, MA) ; Cermak; Nathan; (Cambridge, MA)
; Olcum; Selim; (Cambridge, MA) ; Manalis;
Scott; (Cambridge, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Massachusetts Institute of Technology |
Cambridge |
MA |
US |
|
|
Family ID: |
54063475 |
Appl. No.: |
14/247779 |
Filed: |
April 8, 2014 |
Current U.S.
Class: |
435/287.1 |
Current CPC
Class: |
G01N 9/002 20130101;
G01N 2015/1043 20130101; G01N 2015/0053 20130101; G01N 15/10
20130101 |
International
Class: |
G01N 33/50 20060101
G01N033/50 |
Goverment Interests
[0001] This invention was made with government support under
Contract Number R01GM085457 awarded by the National Institutes of
Health. The government has certain rights in the invention.
Claims
1. Serial suspended microchannel resonator sensor array comprising:
a plurality of resonator cantilevers in fluid communication with
one another; and a plurality of delay channels in fluid
communication with, and disposed between, the resonator
cantilevers; wherein an object introduced into the array will flow
in one direction and be measured by each of the cantilevers in turn
after a selected delay in the delay channels.
2. The array of claim 1 wherein the sensor array is disposed on a
single microfluidic chip.
3. The array of claim 1 further including a piezoresistive readout
of a measured object.
4. The array of claim 1 wherein the resonator sensors are driven by
a piezoelectric shaker.
5. The array of claim 1 wherein each cantilever has a different
length to provide different resonant frequencies to prevent
coupling between resonators.
6. The array of claim 5 wherein the different resonate frequencies
are offset by approximately 10 kHz.
7. The array of claim 1 wherein, the cantilevers operate in the
second or higher vibrational mode.
8. The array of claim 7 wherein fluid channels within the
cantilever extend only to the node of the second vibrational
mode.
9. The array of claim 1 wherein the selected delay in the delay
channels is determined by volume of the delay channels.
10. The array of claim 1 wherein the object is a cell.
Description
BACKGROUND OF THE INVENTION
[0002] This invention relates to suspended microchannel resonators
and more particularly to an array of serially-arranged suspended
microchannel resonators.
[0003] Suspended microchannel resonators are well-known for
measuring properties such as the mass of objects that pass through
the resonator. Suspended microchannel resonators are described in
the references attached hereto. A suspended microchannel resonator
is a fluidic device in which objects pass along a cantilever that
is oscillating. As an object moves along the resonator, the
resonant frequency changes, enabling the measurement of properties
such as mass of the object.
[0004] Suspended microchannel resonators are often used to analyze
cells. In particular, such resonators are often used to assess
cellular growth rate. Prior art single suspended microchannel
resonators have a limited throughput of a few cells per hour. Cell
samples that are to he screened may contain up to 10.sup.5 cells so
that a single suspended microchannel resonator would be too slow to
make a practical screening device.
[0005] It is therefore an object of the invention to provide a
suspended microchannel resonator system capable of a throughput of
up to 10.sup.4 cells per hour.
SUMMARY OF THE INVENTION
[0006] The serial suspended microchannel resonator array disclosed
herein includes a plurality of resonator cantilevers in fluid
communication with one another. A plurality of delay channels are
provided in fluid communication with, and disposed between, the
resonator cantilevers. An object such as a cell introduced into the
array will flow in one direction and be measured by each of the
cantilevers in turn after a selected delay in the delay channels.
In a preferred embodiment, the sensor array disclosed herein is
disposed on a single microfluidic chip. A suitable selected delay
is approximately two minutes in one embodiment of the invention
disclosed herein.
[0007] In a preferred embodiment, the resonator sensors are driven
by a piezoelectric shaker and each of the cantilevers has a
different length to provide different resonant frequencies to
prevent coupling between resonators. A suitable offset in resonant
frequencies is approximately 10 kHz. It is also preferred that the
cantilevers operate in the second or higher vibrational mode. In
this embodiment, fluid channels within the cantilever extend only
to the node of the second vibrational mode.
BRIEF DESCRIPTION OF THE DRAWING
[0008] FIG. 1 is a schematic illustration of the serial suspended
microchannel resonator devices along with delay channels in between
each device.
[0009] FIG. 2 is a schematic illustration of four suspended
microchannel resonators along with the pattern obtained upon cell
passage.
[0010] FIG. 3 is a schematic illustration of a serial suspended
microchannel resonator array including 25 serial arrays, each with
ten resonators.
[0011] FIG. 4 is a schematic illustration of the side view of a
resonator vibrating in a second mode.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0012] With reference first to FIG. 1, a suspended microchannel
array 10 includes plural cantilevers 12. The cantilevers 12 are
separated by serpentine delay channels 14 disposed between each of
the cantilevers 12. As shown in FIG. 1, the cantilevers are
positioned along the same fluidic channel. It is preferred that the
suspended microchannel resonator array 10 be placed on a single
microfluidic chip. Rather than passing a single cell back and forth
through a single sensor to measure growth, a cell will constantly
flow in one direction and be measured by several different sensors,
traversing a cantilever roughly once every two minutes. It will be
appreciated that multiple cells can be measured simultaneously by
the system disclosed herein since each cell only occupies a
cantilever for a short time, and then spends time in the delay
channel. Thus, another cell is free to pass through the suspended
microchannel resonator in the meantime.
[0013] FIG. 2 illustrates the invention with a series of four
cantilevers 12. In practice, it is expected that each cell will be
measured approximately every two minutes over a 22 minute period
and that a single array will be capable of measuring the growth
rate and mass of a cell at a rate of about 400 cells per hour.
[0014] In FIG. 3, the serial design has been parallelized to
provide 25 serial arrays of ten resonators each. The design in FIG.
3 can have a throughput of up to 10,000 cells per hour.
[0015] The design of the devices disclosed herein are very similar
to previous piezoresistive suspended microchannel resonator systems
(1) except. that there will be multiple resonators instead of only
one or two. Thin piezoresistive traces are doped onto bulk silicon
near the base of a resonator, where the silicon experiences maximum
stress, and the resistance is read out via an on-chip Wheatstone
bridge circuit, connected to an off-chip high-bandwidth,
high-input-impedance difference amplifier. Although there is room
for hundreds to thousands of resonators on a single 5 cm.sup.2
chip, the delay channels 14 will ultimately be the limiting factor.
It is estimated that about 25 serial arrays of ten resonators each
with nine two-minute delay channels will be the limit for a chip of
this size.
[0016] In order to run all of the suspended microchannel resonators
12 simultaneously, each resonator must be driven in positive
feedback at which point it becomes an oscillator with a very high
effective quality factor (on the order of 10.sup.10). However, this
feedback loop relies on a method to precisely phase-shift the
position signal before feeding it back to the resonator as a
driving force. To keep all the resonators in feedback
simultaneously, each with its own specific phase-shift, we will
take the summed position signals from each resonator, use an array
of digitally-implemented phase-locked loops to filter and delay the
signal for a digitally-controlled time, and drive the piezoelectric
shaker with this delayed signal. Note that the piezo shaker is
actually driven with the sum of all the different delayed signals
coming from each resonator, each with its own particular delay. The
phase-locked loop operations may be performed with a
field-programmable gate array (FPGA) chip using custom
software.
[0017] To avoid coupling between resonators, the length of the
cantilevers will be adjusted to offset their resonant frequencies
by, for example, 10 kHz. The necessary bandwidth to resolve 99% of
the energy in a particle signal is estimated using Carson's rule
for each resonator. It is estimated that less than 2,200 Hz of
bandwidth, depending on flow rate, between the cantilevers 12 will
be necessary.
[0018] The cantilevers 12 are designed to operate in the second
vibrational mode where, unlike in the first mode, the signal is not
affected by the particle flow path (2). However, one problem we
have had with vibrating cantilevers in higher modes is that the
inertial (centrifugal) force experienced by particles at the tip of
the cantilever becomes substantial (due to a quadratic dependence
of force on frequency), and cells are more likely to become trapped
at the tips of the cantilevers. Especially at slower flow rates
(less than 1 mm/sec in these flow channels), cells becoming stuck
is a common problem and often requires decreasing the cantilever
drive amplitude thereby increasing the noise level of the
measurement. This problem is avoided by designing the cantilevers
such that the internal fluidic channel extends only to the node of
the second vibrational node as shown in FIG. 4. Thus, cells will
never be subjected to the inertial forces that trap them at the end
of the cantilever. Importantly, the high-resolution mass
measurements acquired when cells pass through the antinodes will
not be degraded.
[0019] The delay channels 14 are effectively parameterized by only
the length and cross section. Assuming we know the time delay
desired between two cantilevers At and the target time for a cell
to pass through a single cantilever t.sub.measure, then the
necessary volume of the delay channel is determined. For an
exemplary two-minute delay between cantilevers and a single
cantilever measurement time of one second, the delay channel must
have a volume 120 times the cantilever volume. Therefore, if one
chooses the cross section dimensions, one can calculate the
necessary length. The choice of cross section geometry depends on
two opposing concerns. The first is that a larger cross section
exacerbates problems of unequal flow rates between different cells
and potentially could result in cells passing each other and
changing the arrival order of cells at different cantilevers.
However, a counterargument against small cross sections is that
smaller cross sections increase the possibility of clogging and
increase the fluidic resistance of the channel. As a result of the
high resistance, generating high flow rates to blast out clogs
becomes difficult without resorting to such high pressures that
might damage the microfluidic chip itself. A suitable design for
the delay channels for mammalian cells has a cross section of 19
.mu.m by 30 .mu.m as a compromise between these two competing
concerns.
[0020] As noted above, there may be a loss of ordering in the delay
channels when cells are flowing at different velocities because the
flow's profile is parabolic. A first solution to the problem is to
decrease cell concentration such that the spacing between cells is
larger. Throughput, however, will he lower. A second solution is to
infer when the ordering has changed and still assign peaks to the
correct cells. Because cells vary widely in their masses and grow
slowly, one can cast the problem as an "assignment problem" in
which one seeks to match peaks at sequential cantilevers, using the
assumption that cells do not abruptly change masses, and use
well-known algorithms and (Hungarian algorithms, Needleman-Wunsch)
to find an optimal assignment. Such algorithms have been used
previously for serial operation of dual suspended microchannel
resonators (3).
[0021] The serial microchannel resonator arrays disclosed herein
may be fabricated by using an established process developed for
fabricating piezoresistive suspended microchannel resonators (1,4).
Briefly, wafer bonding of silicon to silicon and silicon to Pyrex
will be used to create free-standing vacuum packaged silicon
microchannels. Devices are vacuum sealed at sub millitorr pressure
and an on-chip getter will be used to insure stability of the low
pressure microenvironment over extended time periods. Bypass
channels for fluid delivery will be etched 30 .mu.m deep into Pyrex
wafers which will be ultrasonically drilled and anodically bonded
to the silicon wafer. Fluidic interconnects to the chip are made by
a Teflon manifold and perfluorelastomer o-rings. Importantly, the
fluid path contacts only silicon and Pyrex which are inert to most
reagents.
[0022] The numbers in parentheses refer to the references listed
herewith. The contents of all of these references are incorporated
herein by reference. It is recognized that modifications and
variations of the invention will be apparent to those of ordinary
skill in the art, and it is intended that all such modifications
and variations be included within the scope of the appended
claims.
REFERENCES
[0023] 1. Lee J, Chunara R, Shen W, Payer K, Babcock K, Burg T P,
Manalis S R. (2011). Suspended microchannel resonators with
piezoresistive sensors. Lab on a Chip, 11(4): 645-51. [0024] 2. Lee
J. Bryan A K, Manalis S R. (2011). High precision particle mass
sensing using microchannel resonators in the second vibration mode.
Review of Scientific Instruments, 82(2). [0025] 3. Bran A K, Hecht
V C, Shen W, Payer K. Grover W H, Manalis S R. (2014). Measuring
single cell mass, volume, and density with dual suspended
microchannel resonators. Lab on a Chip, 14(3): 569-76. [0026] 4.
Burg T P, Gorlin M, Knudsen S M, Shen W, Carlson G, Foster J S,
Babcock K, Manalis S R. (2007). Weighing of biomolecules, single
cells and single nanoparticles in fluid. Nature, 446(7139):
1066-9.
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