U.S. patent application number 11/828133 was filed with the patent office on 2008-06-26 for integrated micro-pump and electro-spray.
Invention is credited to Hsueh-Chia Chang, Zilin Chen, Ping Wang.
Application Number | 20080152509 11/828133 |
Document ID | / |
Family ID | 39543057 |
Filed Date | 2008-06-26 |
United States Patent
Application |
20080152509 |
Kind Code |
A1 |
Chang; Hsueh-Chia ; et
al. |
June 26, 2008 |
INTEGRATED MICRO-PUMP AND ELECTRO-SPRAY
Abstract
Disclosed is a micro-pump having at least one channel on a
substrate where the channel has an inlet and an outlet. The
micro-pump includes a first and second electrode coupled to the
substrate, wherein the electrodes deliver a current that produces
an electric field across the substrate to create a flow from the
inlet to the outlet of a fluid contained in the channel. The
micro-pump also includes an ion-specific membrane housing for the
electrode reservoir minimizes bubble generation, fluid leakage and
pressure loss. Further, at least a portion of the channel contains
a chemically formed porous matrix.
Inventors: |
Chang; Hsueh-Chia; (Granger,
IN) ; Chen; Zilin; (Mishawaka, IN) ; Wang;
Ping; (Mishawaka, IN) |
Correspondence
Address: |
HANLEY, FLIGHT & ZIMMERMAN, LLC
150 S. WACKER DRIVE, SUITE 2100
CHICAGO
IL
60606
US
|
Family ID: |
39543057 |
Appl. No.: |
11/828133 |
Filed: |
July 25, 2007 |
Current U.S.
Class: |
417/51 ;
250/282 |
Current CPC
Class: |
F04B 43/043
20130101 |
Class at
Publication: |
417/51 ;
250/282 |
International
Class: |
F04B 37/10 20060101
F04B037/10 |
Goverment Interests
GOVERNMENT INTEREST STATEMENT
[0002] The United States Government has rights in this invention
pursuant to Contract No. DAAB 07-03-3-K414 with the United States
Army.
Foreign Application Data
Date |
Code |
Application Number |
Feb 24, 2006 |
US |
PCT/US06/06457 |
Claims
1. A micro-pump comprising: a substrate having at least one
channel, wherein the channel has an inlet and an outlet; a first
and second electrode coupled to the substrate, wherein the
electrodes deliver a current that produces an electric field across
the substrate to create a flow from the inlet to the outlet of a
fluid contained in the channel; and at least a portion of the
channel contains a chemically formed porous matrix.
2. The micro-pump as defined in claim 1, wherein the matrix is
formed from a sol-gel chemical process.
3. The micro-pump as defined in claim 1, wherein the matrix is
formed by fusing nano-porous beads.
4. The micro-pump as defined in claim 1, wherein the matrix is at
least one of monolithic or formed from a silica precipitate.
5. The micro-pump as defined in claim 1, wherein matrix has a
plurality of pores.
6. The micro-pump as defined in claim 1, wherein the matrix has
charged surfaces.
7. The micro-pump as defined in claim 1, wherein the micro-pump is
used in a total analytical system.
8. The micro-pump as defined in claim 7, wherein the total
analytical system is at least one of: a mass spectrometer, a
biochip, a diagnostic equipment, an implantable drug delivery
device, a circuit cooling device, a device used for micro-fuel cell
applications, or a capillary electrophoresis chromatograph.
9. The micro-pump as defined in claim 1, further comprising at
least one electrode that is coupled to a conducting membrane that
blocks ion responsible for electro-chemical reactions at the
electrode.
10. The micro-pump as defined in claim 9, wherein the membrane
minimizes bubbles in the at least one channel.
11. The micro-pump as defined in claim 1, wherein the micro-pump is
coupled to an electro-spray forming a combination integrated with
the substrate, wherein the electro-spray emits the fluid from the
at least one channel.
12. The micro-pump as defined in claim 11, wherein the combination
is one of at least disposable or portable.
13. The micro-pump as defined in claim 11, wherein the combination
sustains a high pressure.
14. The micro-pump as defined in claim 11, wherein the combination
maintains precise low flow rates.
15. The micro-pump as defined in claim 11, wherein the fluid is
emitted from the at least one channel via a Taylor cone.
16. The micro-pump as defined in claim 11, wherein the
electro-spray may operate with less than 100 micro-liter
samples.
17. The micro-pump as defined in claim 11, wherein the fluid is an
organic material.
18. A method of creating a porous matrix in a channel in a
substrate for use in an integrated micro-pump and electro-spray,
the method comprising: inserting a chemical mixture into at least a
portion of the channel; inserting silica beads to control
precipitated bead and pore size; heating the mixture until a
precipitate forms; and cooling the channel and the precipitate.
19. The method as defined in claim 18, wherein the precipitate
forms a monolithic matrix.
20. The method as defined in claim 18, wherein the mixture is
formed from a sol-gel process.
21. The method as defined in claim 18, wherein the matrix is silica
precipitate.
22. The method as defined in claim 18, wherein the channel is
cleaned before the mixture is inserted.
23. The method as defined in claim 18, wherein the matrix forms
micro-pores.
24. The method as defined in claim 18, wherein the surface of the
matrix has nano-pores.
25. The method as defined in claim 18, wherein the matrix may be
used in at least one of aqueous and organic solutions.
26. A means of creating a porous matrix for use in an integrated
micro-pump and electro-spray, the means including: means for
forming a chemical mixture; means for inserting the chemical
mixture into at least a portion of a channel formed in a substrate;
means for heating the mixture until a precipitate forms; and means
cooling the channel and the precipitate.
Description
RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent
Application No. 60/655,437, entitled "Integrated DC
pump/electro-spray," filed on Feb. 24, 2005, and PCT Application
No. PCT/US06/06457, entitled "Integrated Micro-Pump and
Electro-Spray," filed on Feb. 24, 2006, both of which are hereby
incorporated by reference in their entireties.
FIELD OF THE DISCLOSURE
[0003] This disclosure relates generally to micro-fluidic pumping
and spraying devices, and, more particularly, to an integrated DC
micro-pump and electro-spray and methods for manufacturing the
same.
BACKGROUND
[0004] A Total Analytical System (TAS) is a chemical analysis
system that automates all necessary steps for analysis of a
chemical substance (e.g. sampling, transport, filtration, dilution,
chemical reactions, separation and detection). Considerable effort
in analytical chemistry has been directed toward the
miniaturization of these systems to enable rapid, portable, and
automated analyses of small-volume samples. Ideally, a micro-TAS
(t-TAS) integrates all function units necessary to analyze a
chemical sample on a single micro-fluidic substrate, sometimes
referred to as a "lab-on-a-chip." Because the flow velocity in a
micro-channel scales as the channel radius squared, scaling down
the system by a factor of n requires an n.sup.2 increase in the
driving pressure to maintain the same velocity. As such, a notable
component of a .mu.-TAS is a powerful micro-fluidic pump capable of
generating high pressure. Moreover, this pump may be integrated
into the entire system on the same substrate because fluid transfer
from an external pump may defeat many of the advantages of .mu.-TAS
and may require tedious tubing connection for each run. Constant
high-pressure but low flow rates for micro- and nano-liter samples
and especially pulsation-free flows are often the primary pump
requirements for micro-flow injection analysis (.mu.-FIA),
micro-column liquid chromatography (P-LC), and other t-TAS.
[0005] One micro-pump that has been proposed for use with .mu.-TAS
is the electroosmotic pump (EOP), which uses electric current to
cause a bulk fluid movement through a system. EOPs typically suffer
from several major problems. One possible problem is that, with
open channel or capillary EOPs, there is a low stall pressure and,
therefore, these EOPs are generally not used in systems with
high-pressure loads. High-pressure build-up can be achieved if the
pump channel is smaller or if a dense packing material is used to
produce large hydrodynamic resistance. Unlike mechanical pumps,
which generate a local high pressure and for which hydrodynamic
resistance in the pump would reduce this driving pressure, pure
electroosmotic flow does not produce a pressure field, but instead
relies on hydrodynamic resistance to reduce the flow and build a
high pressure along the pump channel. Hence, in a counter-intuitive
manner, EOP pump channels need to be as small as possible. However,
a single pump channel cannot produce enough flow and a large bundle
of small micro-channels is needed for the EOP.
[0006] Another potential problem is electrolytic bubble generation,
because of the large current in the open channel. In aqueous
solutions, when the applied electrode potential exceeds a threshold
approximately 1.1 V, significant electrolysis and other electrode
reactions may occur, producing ions that contaminate the sample and
generate bubbles, which block the micro-channels. To eliminate this
blockage, a bubble-releasing device may be used downstream of the
pump, or alternatively, the electrodes may be placed in isolated
open reservoirs such that bubbles can escape and the ions cannot
invade the flow channel. However, the reservoir housing should be a
conductor to enable electric field penetration. The traditional
solution to the reaction problem is to reduce the current by using
dense packing. Depending on the type of packing used, too dense a
packing may be undesirable because it can create or further
aggravate clogging problems.
[0007] Because both the low-pressure and electrode reaction
disadvantages of EOPs can be reduced by dense packing within the
pump channel, considerable effort has been devoted to fabrication
of multiple micro-channels by lithography or internal packing with
high surface charge density that still allows electroosmotic flow.
One strategy is to pack the pump channel with small particles.
[0008] An attempt at this is shown in FIG. 1, which illustrates a
portion of conventional micro-pump 100. The conventional pump 100
is formed in a substrate 102. The substrate has a channel 104 that
includes an inlet 106 and an outlet 108. An electrolyte flows
through the inlet past a packing 110 to the outlet 108. The packing
110 is made of a plurality of micro-beads 112. The micro-beads 112
are packed into the channel 104 through the inlet 106. The channel
104 further includes a filter 114 that holds the micro-beads 112
together as the packing 110 because the opening of the filter 114
has a dimension smaller than the length of the diameter of the
micro-beads 112.
[0009] The presence of the micro-beads 112 increases the pressure
in the channel 104, which assists in the operation of the pump 100,
as described above. However, in addition to clogging problems that
a dense packing can create, the installation of the micro-beads 112
is oftentimes extremely tedious, time-consuming and expensive.
[0010] In other conventional pumps, a high pressure is created by
etching small channels into a substrate. Etched channels can reach
dimensions on the micrometer scale, but the etching process is also
oftentimes tedious and expensive. Further, a simply-etched channel
would not contain a porous material. Thus, several etched channels
may need to be formed in a substrate to achieve optimal pressure in
the pump. Repeating the etching process directly affects the key
metrics of the manufacturing process, i.e., time and cost.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic illustration of a prior art micro-pump
with micro-bead packing.
[0012] FIG. 2 is a schematic diagram of an example integrated
micro-pump and electro-spray.
[0013] FIG. 3 is a photograph of a magnified example monolithic
matrix in an example capillary.
[0014] FIG. 4 is a graph plotting pump curves (pressure versus flow
rate) for the example micro-pump of FIG. 1 at different voltages
using acetonitrile as the pumping fluid.
[0015] FIG. 5 is a photograph of a magnified Taylor cone emitting
from the example electro-spray of FIG. 1.
[0016] FIG. 6 is a schematic diagram of the example integrated
micro-pump and electro-spray as a front-end to a mass
spectrometer.
[0017] FIG. 7 is an example mass spectrum of example amino acid
peaks generated by the example mass spectrometer with front-end
integrated micro-pump and electro-spray of FIG. 6
DETAILED DESCRIPTION
[0018] An example micro-pump of the illustrated examples includes a
substrate that has at least one channel, and the substrate
integrates a micro-pump and electro-spray. Further, the example
apparatus includes a porous matrix that is formed from a chemical
process, as described herein.
[0019] FIG. 2 is a schematic diagram of an example analytical
apparatus 200, which generally includes a micro-pump 210 and an
electro-spray 212, as described in greater detail below. The
analytical apparatus 200 may be utilized in a .mu.-TAS as described
below. The analytical apparatus 200 includes a substrate 202
through which at least one channel 204 extends. The substrate 202
may be formed of any suitable material, including, for example, an
inexpensive material such as fused silica. The channel 204 has an
inlet 206 and an outlet 208. The micro-pump 210 is coupled to the
channel 204 toward or at the inlet 206, and the electro-spray 212
is coupled to the outlet 208. In some example designs, the
micro-pump 210 and electro-spray 212 may occupy distinct portions
of the substrate 202 or, as illustrated in FIG. 2, the micro-pump
210 and electro-spray 212 may overlap. Fluid such as, for example,
a solvent, electrolyte or biological sample flow through the
channel 204.
[0020] The micro-pump 210 includes a power supply 214, which may
include, for instance, batteries and micro-amplifiers, and wires
216 that connect the power supply to electrodes 218, 219. The
electrodes 218, 219 are coupled to the substrate 202, either
directly, via reservoirs or other materials, as described in
greater detail below. In the example micro-pump 210, which operates
as an electroosmotic micro-pump, the power supply 214 provides a
high voltage and a direct current (DC). The power supply 214 is
used to create an electric field across the substrate 202. The
walls 220 of the channel or capillary 204 have electric charges,
and an electric double layer of counter ions spontaneously forms at
the walls 220, where the counter ions may be driven by the power
supply. When the tangential electric field is applied, ions in the
double layer suffer a Coulombic force, called the Maxwell force,
and move toward the electrode of opposite polarity. This creates
motion in the fluid near the walls 220. The motion at the walls 220
transfers momentum via viscous forces into the bulk of the fluid in
the channel 204, creating flow from inlet 206 to outlet 208.
[0021] The illustrated electroosmotic micro-pump 210 has no moving
parts and is advantageously relatively inexpensive to manufacture.
Accordingly, if desired, the electroosmotic micro-pump 210 may be
disposable with the rest of the analytical apparatus 200.
[0022] Further, because the fluid in the channel 204 is charged,
the flow from the micro-pump 210, driven by the applied electric
field, carries most of the current. Consequently, the flow rate and
current are strongly correlated. Precise flow control can be
achieved with a simple current or voltage-controlled circuit (not
shown). In addition, for the example micro-pump 210, the flow
carried current (convective current) may exceed the usual current
due the applied electric field.
[0023] The channel 204 of the micro-pump 210 also include a packing
such as a matrix 222 that, in addition to overcoming low pressure
and chemical reactions at the electrodes in the channel 204,
separates and further transports the fluid sample. In this example,
the matrix 222 that may occupy up to two-thirds of the channel 204,
but it will be appreciated that the matrix 222 may occupy any
percentage of the channel 204 as desired. The skeleton or matrix
222 may be, for example, a monolithic matrix and/or a silica-based
matrix. Silica has an intrinsic ability to generate a strong
electroosmotic flow due to the presence of ionizable silanol groups
at the surface of the matrix 222. In fact, a silica monolith matrix
has a bimodal pore distribution whose nano-porous structure, which
as discussed in more detail below, produces a higher charge density
than regular fused-silica glasses, i.e., the substrate 202 alone,
or non-porous silica particles. The silanol groups at the
fused-silica capillary walls 220 can be easily cross-linked to the
matrix 222 to assure secure linkage. Thus, support structures, such
as frits, are unnecessary to hold the matrix 222 in place. Because
frits may cause pressure drops to occur, the efficiency of the
micro-pump 210 increases with the use of the matrix 222 and the
absence of frits.
[0024] It may be desirable to have high pressure and large flow
rate in the channel 204. These metrics are competing principles
because the high hydrodynamic resistance offered by a small pore
size is responsible for high pressure, while large pore-size with
large cross-sectional areas is desirable for a large flow rate. The
example analytical apparatus 200 uses a bundle of parallel
micro-channels with small pore size to optimize performance based
on the competing principles. However, the pore size should not be
smaller than the double layer thickness, as polarization, Maxwell
force and flow would all diminish significantly. Hence, an example
advantageous structure is a porous medium with parallel pores whose
radius is comparable to the double layer thickness. In fact, one
optimum channel dimension is roughly the double layer thickness of
the pumping fluid, which ranges from 10 nanometers to 1 micron. At
this dimension, the fluid within the channel is fully charged with
counter-ions up to its maximum capacitance. The matrix 222 offers
such a structure with a small pore radius that approaches the
double layer thickness of some polar organic liquids
[0025] In an exemplary embodiment, the matrix 222 is formed by a
chemical process such as, for example, a sol-gel process. To form
the matrix 222, it may first be desirable to clean the capillary
204. To that end, the fused-silica capillary 204 may be flushed
with a cleansing agent such as, for example, acetone and then baked
to remove all liquids inside. This pretreatment substantially
eliminates impurities inside the capillary 204. After, or despite a
cleansing, a chemical mixture is then inserted into the channel
204. In one example, the mixture may include 0.5 mL of 0.01 M
acetic acid, 54 mg of polyethylene glycol and 0.2 mL of
tetramethoxysilane that are mixed in a micro-liter size vial bottle
and stirred for about 30 minutes in an ice-water bath (0.degree.
C.). The matrix pore size can be controlled by adjusting the
composition of the solution. In some cases, sub-micron silica beads
are inserted in the solution to promote subsequent precipitation of
more beads and to control the size of the pore size. When all the
polyethylene glycol is dissolved and a transparent single-phased
solution is observed, the solution is then introduced inside the
channel 204. Then mixture is then heated. Eventually, the heated
mixture transforms, at least in part, into silica precipitate. The
precipitated beads are fused together by the heat. An example
heating process includes heating the solution-filled channel 204 in
an oven at 40.degree. C. for 12 hours. Then the temperature is
increased from 40.degree. C. to 300.degree. C. at a rate of
1.degree. C./minute, soaking the capillary 204 for 4 hours at each
of 80.degree., 120.degree., 180.degree., and 300.degree. C.
Finally, the capillary 204, with the silica precipitate, is cooled
to room temperature at a rate of 1.degree. C./minute. Accordingly,
the crystallization of the silica prepared by the sol-gel process
forms the continuous matrix 222 that has micrometer-sized through
pores 224, the size of which can be adjusted by the synthesis
procedure from approximately 10 nanometers to approximately 10
microns. This range is approximately equal to the double layer
thickness of many solvents. The matrix 222 also has nano-porous
surfaces 226 (FIG. 3). In this embodiment, the matrix 222 is
naturally coupled to the walls 220 of the capillary 204. The
silica-based matrix 222 is generally superior to polymeric
monoliths in its mechanical strength and high stability in both
aqueous and organic solutions.
[0026] The surface charge of the matrix 222 and/or the dimension of
the micro-pores 224 and nano-pores 226 can be adjusted by
chemically functionalizing the surface through silica chemistry,
i.e., by adjusting the composition of the sol-gel solution during
synthesis. Thus, the structure of the matrix 222 can be adjusted
without additional equipment. This allows for easy adjustments to
meet special requirements such as at low pH conditions. It also
allows the matrix to act as a chromatograph packing or a catalytic
surface.
[0027] Because of the disassociation of silanol groups on the
nano-porous matrix 222, the surface of the matrix 222 has high
charge density. This charge density, in combination with the low
conductivity and micrometer-sized pores 224 of the matrix 222,
result in large hydrodynamic resistance. Thus, the matrices 222 are
ideal for electroosmotic micro-pumps, such as the micro-pump 210.
FIG. 3 illustrates one example of the structure of the resultant
matrix 222 formed by the above example process. As shown in FIG. 3,
the illustrated matrix 222 is a very porous structure, both in
terms of the micro-pores 224 between branches of the matrix 222 and
the nano-pores 226 on the surface of the matrix 222. These pores
range anywhere from about 10 nanometers to 10 microns in width;
however, the pores may be larger or smaller depending upon the
desired application.
[0028] The analytical apparatus 200 may also include a nonpermeable
membrane such as, for example, a NAFION.RTM. membrane 224, at the
downstream electrode reservoir 219 as shown in FIG. 2. In the
illustrated example of FIG. 2, the NAFION.RTM. membrane 224 is used
with the cathode. In other examples, the NAFION.RTM. membrane 224
may be used with both electrodes 218, 219. The NAFION.RTM. membrane
224 is a conduction membrane but, in this embodiment, is not
permeable to fluid flow. Thus, the cathode is hydrodynamically
isolated from the pump channel 204 such that there is no flow
exchange between the electrode reservoir 219 and the channel 204.
The NAFION.RTM. membrane 224 hence offers even more hydrodynamic
resistance and further enhances pump pressure.
[0029] The NAFION.RTM. membrane 224 allows the electric field and
specific ions to penetrate but not the ions responsible for
electro-chemical reactions at the electrode 219. As a result, a
large voltage (e.g., greater than several kilovolts) can be applied
through the capillary 204 of the matrix 222 without producing or
introducing electrolytic bubbles or ions in the capillary 204.
Thus, in addition to minimizing fluid leakage and pressure loss,
the ion-specific NAFION.RTM. membrane 224 minimizes bubble
generation. Bubbles may be disadvantageous where they block the
micro-channels 224 and/or contaminate the sample. Ions also have
the potential to contaminate the matrix 222. Although there may be
negligible bubble generation because of the low current through the
low-conducting matrix 222, i.e., the minimum current of less than
100 .mu.A has a reduced bubble generation to such an extent that
any bubbles would dissolve in the fluid. Further, because the
NAFION.RTM. membrane 224 is impermeable to fluid flow including
ions responsible for electro-chemical reactions, the NAFION.RTM.
membrane 224 also minimizes the problems caused by pH generation at
the electrode 219.
[0030] As described above, high pressure is desirable and the
example micro-pump 210 is capable of sustaining high pressures. In
fact, in one example, the micro-pump 210 can sustain pressures
greater than 4 atmospheres, depending upon the fluid use as a
sample, while maintaining precise low flow rates such as, for
example, less than a microliter/minute. The low flow rate allows
the micro-pump 210 to successfully operate with small samples.
Pressure as high as several atmospheres may be achieved within a
100 micron capillary 203. A maximum pressure exceeding 20
atmospheres may be achieved with larger capillaries and the
smallest through pores 224.
[0031] FIG. 4 illustrates an exemplary pump curve for the DC
electroosmotic micro-pump 210 of FIG. 2 at different voltages and
with acetonitrile as the pumping fluid. Organic solvents like
methanol, ethanol, and acetone may also be used. Low-conductivity
electrolytes such as, for example, de-ionized water can also be
used. It can be seen from the curve that the micro-pump 210 with
the matrix 222 can generate pressure as high as approximately 1.2
atmospheres when a potential of 6 kV is applied and acetonitrile is
used as the test fluid. Thus, the electroosmotic micro-pump 210
with the matrix 222, with its high pressure and low current, is
ideal to dive flow against large loads in micro-systems such as
.mu.-LC, .mu.-FIA, and micro-chip sensors. Other pressures are
achievable when other fluids are used in the channel 204, depending
on the properties of the fluid sample used.
[0032] Returning to FIG. 2, the outlet 208 of the channel 204 is
coupled to an electro-spray 212. The electro-spray 212, or
nano-spray, generates small ions or droplets 230 that are easily
ionized over a broad range of flow rates for any general sample.
For example, the electro-spray 212 may produce a Taylor cone 228,
which is a cone of fluid that emits the small charged droplets 230.
Multiple Taylor cones may form at the outlet 208 if there are
multiple paths through the matrix 222. An example Taylor cone 228
is shown in FIG. 5. The electro-spray 212 is able to form the
stable Taylor cone 228 because of the high pressure the micro-pump
210 can deliver. Further, in this embodiment, the micro-pump 210
can maintain these high pressures with less than a 100 micro-liter
sample. In addition the integration of a DC micro-pump with the
matrix 222 into the device 200 with the electro-spray 212 allows
for highly controllable sample flow-rates at as little as
approximately a pico-liter per second. This allows easy sample
delivery of small samples from the substrate 202 to another
analytical device such as, for example, a mass spectrometer, or any
other suitable device that could not be integrated into the same
substrate 202, which is discussed in more detail below.
[0033] The use of the porous matrix 222 in combination with the
electro-spray 212 may have several distinct advantages over most
commercially available nano-sprays that were designed specifically
to process small sample volumes. The multiplicity of flow paths in
the matrix 222 results in fewer clogging problems even when used
with organic or normal-phase samples, an issue that plagues most
existing nano-sprays. Other benefits have been described herein
such as, for example, the ability to pump and spray normal-phase
sample, such as organic fluids.
[0034] There is a focused electric field at the Taylor cone 228
that causes charges (typically ions of the same polarity as the
walls 220 at the outlet 208) to concentrate at the tip of the
Taylor cone 228. When the charge density becomes excessive,
sub-micron charged droplets 230 are emitted from the Taylor cone
228. With evaporation of the solvent in flight, the charge density
of the droplets 230 increases because the solvent within the
droplet 230 evaporates but the droplet 230 remains charged. Because
the volume of the droplet 230 decreases rapidly, the surface
tension of the droplet 230 is unable to oppose the electrostatic
repulsive forces of the charges within the droplet 230. This causes
the droplet 230 to explode into many smaller droplets 230. This is
known as Rayleigh fission. The final droplets 230 are nanometer in
dimension and contains charged (ionized) molecules that will be
identified in any adjoined .mu.-TAS. In FIG. 6, the example
adjoined .mu.-TAS is a mass spectrometer 300. The electro-spray 212
may be used as a front-end or interface with many other .mu.-TAS or
other analytical devices as well including, for example, biochips,
diagnostic equipment, an implantable drug delivery device, a
circuit cooling device, a device used for micro-fuel cell
applications, and/or a capillary electrophoresis chromatograph.
[0035] Referring now to FIG. 6, mass spectrometers are commonly
known, particularly for use with the detection of trace quantities
of contaminants or other toxins, and will not be discussed here in
great detail. However, in brief: in the mass spectrometer 300 of
FIG. 6, the droplets 230 formed by the analytical apparatus 200
accelerate through an ion analyzer 302, which in this example is a
quadruple ion analyzer 302. The ion analyzer 302 uses positive and
negative voltages to control the paths of the droplets 230. The
droplets 230 travel down the path based on their mass to charge
ratio; therefore, the path of a droplet 230 will depend on its
mass. The droplet 230 eventually hits a detector 304. The detector
304 works by producing an electric signal when struck by a charged
droplet 230. The detector 304 determines which droplets 230 have
struck the detector 304 and a spectrum is produced. An example
spectrum is shown in FIG. 7, which accurately identifies peptide
and amino acids.
[0036] To generate a cone 228 that can be used as a front-end to a
mass spectrometer, considerable pressure typically needs to be
sustained at the orifice where the cone 228 is situated. This
usually requires large, expensive pumps. However, as described
above, the micro-pump 210 with the matrix 222 is capable of
producing and sustaining adequate high pressure for the
electro-spray 212 to be properly used as the front-end of the mass
spectrometer 300. Further, the micro-pump 210 is integrated with
the electro-spray 212 together forming a analytical apparatus that
is cheap to manufacture, disposable so it does not need to be
cleaned or sterilized and portable so it can be used in the
field.
[0037] Although certain example methods, apparatus and articles of
manufacture have been described herein, the scope of coverage of
this patent is not limited thereto. On the contrary, this patent
covers all methods, apparatus and articles of manufacture fairly
falling within the scope of the appended claims either literally or
under the doctrine of equivalents.
* * * * *