U.S. patent application number 10/302560 was filed with the patent office on 2003-06-12 for probes with hydrophobic coatings for gas phase ion spectrometers.
This patent application is currently assigned to Ciphergen Biosystems, Inc.. Invention is credited to Beecher, Jody, Landgraf, William, Scheufele, Frank, Voivodov, Kamen, Weinberger, Scot.
Application Number | 20030106997 10/302560 |
Document ID | / |
Family ID | 26829692 |
Filed Date | 2003-06-12 |
United States Patent
Application |
20030106997 |
Kind Code |
A1 |
Beecher, Jody ; et
al. |
June 12, 2003 |
Probes with hydrophobic coatings for gas phase ion
spectrometers
Abstract
This invention provides a mass spectrometry probe including a
substrate having a surface and a film that coats the surface. The
film includes openings that define features for the presentation of
an analyte. The film also has a lower surface tension that the
surface tension of the substrate surface, and has a water contact
angle between 120.degree. and 180.degree..
Inventors: |
Beecher, Jody; (Boston,
MA) ; Scheufele, Frank; (Palo Alto, CA) ;
Voivodov, Kamen; (Hayward, CA) ; Weinberger,
Scot; (Montara, CA) ; Landgraf, William; (Palo
Alto, CA) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
Ciphergen Biosystems, Inc.
Fremont
CA
|
Family ID: |
26829692 |
Appl. No.: |
10/302560 |
Filed: |
November 21, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10302560 |
Nov 21, 2002 |
|
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09561604 |
Apr 27, 2000 |
|
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6555813 |
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60131653 |
Apr 29, 1999 |
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Current U.S.
Class: |
250/288 |
Current CPC
Class: |
Y10S 977/881 20130101;
Y10S 977/892 20130101; Y10T 436/255 20150115; B01L 3/5085 20130101;
Y10S 977/891 20130101; H01J 49/0418 20130101 |
Class at
Publication: |
250/288 |
International
Class: |
H01J 049/04 |
Claims
What is claimed is:
1. A probe that is removably insertable into a gas phase ion
detector comprising: a) a substrate having a surface adapted to
present an analyte to an ionization source and b) a film that coats
the surface, wherein the film: i) comprises at least one opening
that exposes the surface, thereby defining a feature for applying a
liquid comprising an analyte; ii) has a water contact angle of
between 120.degree. and 180.degree.; and iii) has less surface
tension than the substrate-surface, whereby a liquid applied to the
feature is sequestered in the feature.
2. The probe of claim 1 wherein the film comprises a perfluorinated
hydrocarbon, halogenated hydrocarbon, aliphatic hydrocarbon,
aromatic hydrocarbon, polysilane, organosilane or combinations
thereof.
3. The probe of claim 1 wherein the film comprises a perfluorinated
hydrocarbon.
4. The probe of claim 1 wherein the film comprises a plurality of
openings arranged in a regular array.
5. The probe of claim 1 wherein the film is electrically
conductive.
6. The probe of claim 2 wherein the substrate surface comprises
metal.
7. The probe of claim 2 wherein an adsorbent comprising a binding
functionality is attached to the feature.
8. A system comprising: a) a gas phase ion detector comprising an
inlet port; and b) a probe of claim 1 inserted into the inlet
port.
9. The system of claim 8 wherein the gas phase ion detector is a
mass spectrometer.
10. The system of claim 9 wherein the mass spectrometer is a laser
desorption mass spectrometer.
11. A method of detecting an analyte comprising: a) placing the
analyte on a feature of a surface of a probe of claim; b) inserting
the probe into an inlet port of a gas phase ion detector
comprising: i) an ionization source that desorbs the analyte from
the probe surface into a gas phase and ionizes the analyte; and ii)
an ion detector in communication with the probe surface that
detects desorbed ions; c) desorbing and ionizing the analyte with
the ionization source; and d) detecting the ionized analyte with
the ion detector.
12. The method of claim 11 wherein the gas phase ion detector is a
mass spectrometer.
13. The method of claim 12 wherein the mass spectrometer is a laser
desorption mass spectrometer.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] This application claims priority to provisional application
U.S. Ser. No. 60/131,652, filed Apr. 29, 1999, the disclosure of
which is herein incorporated by reference in its entirety.
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED
RESEARCH AND DEVELOPMENT
[0002] Not Applicable.
BACKGROUND OF THE INVENTION
[0003] This invention is directed to the field of mass spectrometry
and, more particularly, to sample probes with hydrophobic coatings
for improved sequestration of a liquid sample to a probe
feature.
[0004] Modem laser desorption/ionization mass spectrometry
("LDI-MS") can be practiced in two main variations: matrix assisted
laser desorption/ionization ("MALDI") mass spectrometry and
surface-enhanced laser desorption/ionization ("SELDI"). In MALDI,
the analyte, which may contain biological molecules, is mixed with
a solution containing a matrix, and a drop of the liquid is placed
on the surface of a probe. The matrix solution then co-crystallizes
with the biological molecules. The probe is inserted into the mass
spectrometer. Laser energy is directed to the probe surface where
it desorbs and ionizes the biological molecules without
significantly fragmenting them. However, MALDI has limitations as
an analytical tool. It does not provide means for fractionating the
sample, and the matrix material can interfere with detection,
especially for low molecular weight analytes. See, e.g., U.S. Pat.
No. 5,118,937 (Hillenkamp et al.), and U.S. Pat. No. 5,045,694
(Beavis & Chait).
[0005] In SELDI, the probe surface is modified so that it is an
active participant in the desorption process. In one variant, the
surface is derivatized with affinity reagents that selectively bind
the analyte. In another variant, the surface is derivatized with
energy absorbing molecules that are not desorbed when struck with
the laser. In another variant, the surface is derivatized with
molecules that bind the analyte and that contain a photolytic bond
that is broken upon application of the laser. In each of these
methods, the derivatizing agent generally is localized to a
specific location on the probe surface where the sample is applied.
See, e.g., U.S. Pat. No. 5,719,060 (Hutchens & Yip) and WO
98/59361 (Hutchens & Yip).
[0006] The two methods can be combined by, for example, using a
SELDI affinity surface to capture an analyte and adding
matrix-containing liquid to the captured analyte to provide the
energy absorbing material.
[0007] In the practice of mass spectrometry, localizing the sample
on the probe surface provides advantages. Localization provides
more concentrated sample at the point of laser application. In the
affinity version of SELDI, localization can be important because it
allows the affinity reagent to capture more of the analyte, thereby
providing greater sensitivity of detection. However, liquid samples
tend to spread out over the surface of the probe, thwarting
localization. This especially creates problems when the probe is
designed to hold multiple samples and the samples cannot be
sequestered to specific locations.
[0008] There is a need for better means for sequestering a liquid
sample to a location on a probe surface.
SUMMARY OF THE INVENTION
[0009] This invention provides a mass spectrometry probe capable of
sequestering liquid samples to specific locations, or features, of
the probe surface. The probes comprise a substrate having a surface
and a film that coats the surface. In general, samples used in mass
spectrometry are dissolved in aqueous solutions. Therefore, the
film is selected to be more hydrophobic than the surface (lower
surface tension).
[0010] These coatings provide several advantages compared with
mechanical borders. First, they avoid electrical field
perturbations that hamper mass resolving power and mass accuracy.
Second, they avoid areas of possible sample pooling and
preferential crystallization in regions other than the probed area.
Third, they avoid the need for maintaining strict mechanical
tolerances such as in the case of elevated sample ridges or
depressed sample wells, which can result in poor molecular weight
determination accuracy and precision. Fourth, they avoid, unlike
elevated margins, an optical stop which limits the probed area.
[0011] One solution to the problem that is not as effective
involves manually applying a hydrophobic circle to the probe
surface. The circle can be applied using a PAP pen, available from
Polysciences (Warrington, Pa., USA). The PAP pen includes a
hydrophobic material in an organic solvent base contained in a
stylus. The coating is applied by drawing an enclosed line with the
stylus on the substrate surface. The material delivered by the PAP
pen has a contact angle of about 90.degree..
[0012] In one aspect this invention provides a probe that is
removably insertable into a gas phase ion detector (e.g., a mass
spectrometer) comprising: a) a substrate having a surface adapted
to present an analyte to an ionization source and b) a film that
coats the surface, wherein the film: i) comprises at least one
opening that exposes the surface, thereby defining a feature for
applying a liquid comprising an analyte; ii) has a water contact
angle of between 120.degree. and 180.degree.; and iii) has less
surface tension than the substrate surface, whereby a liquid
applied to the feature is sequestered in the feature.
[0013] In another aspect this invention provides a system
comprising: a gas phase ion detector comprising an inlet port; and
a probe of this invention inserted into the inlet port.
[0014] In another aspect this invention provides a method of
detecting an analyte comprising: a) placing the analyte on a
feature of a surface of a probe of this invention; b) inserting the
probe into an inlet port of a gas phase ion detector comprising: i)
an ionization source that desorbs the analyte from the probe
surface into a gas phase and ionizes the analyte; and ii) an ion
detector in communication with the probe surface that detects
desorbed ions; c) desorbing and ionizing the analyte with the
ionization source; and d) detecting the ionized analyte with the
ion detector.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 shows a sample mass spectrometry probe with of this
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0016] I. Definitions
[0017] Unless defined otherwise, all technical and scientific terms
used herein have the meaning commonly understood by a person
skilled in the art to which this invention belongs. The following
references provide one of skill with a general definition of many
of the terms used in this invention: Singleton et al., Dictionary
of Microbiology and Molecular Biology (2.sup.nd ed. 1994); The
Cambridge Dictionary of Science and Technology (Walker ed., 1988);
The Glossary of Genetics, 5.sup.th Ed., R. Rieger et al. (eds.),
Springer Verlag (1991); and Hale & Marham, The Harper Collins
Dictionary of Biology (1991). As used herein, the following terms
have the meanings ascribed to them unless specified otherwise.
[0018] "Gas phase ion spectrometer" refers to an apparatus that
measures a parameter which can be translated into mass-to-charge
ratios of ions formed when a sample is ionized into the gas phase.
Generally ions of interest bear a single charge, and mass-to-charge
ratios are often simply referred to as mass.
[0019] "Mass spectrometer" refers to a gas phase ion spectrometer
that includes an inlet system, an ionization source, an ion optic
assembly, a mass analyzer, and a detector.
[0020] "Laser desorption mass spectrometer" refers to a mass
spectrometer which uses laser as an ionization source to desorb an
analyte.
[0021] "Probe" refers to a device that is removably insertable into
a gas phase ion detector (e.g., a mass spectrometer) that comprises
a substrate having a surface adapted for the presentation of an
analyte for detection. The probes may be modified as a result of
the analysis and may be disposable.
[0022] "Substrate" refers to a solid material that is capable of
supporting an analyte.
[0023] "Surface" refers to the exterior or upper boundary of a body
or a substrate.
[0024] "Film" refers to thin coating of a polymeric material or a
molecular organic material (e.g., a Langmuir-Blodgett film or a
self-assembling monomer).
[0025] "Surface tension" refers to the reversible work required to
create a unit surface area at constant temperature and pressure and
composition. Surface tension is measured by: g=(dG/dA)T,P,n where
g=the surface tension; G=Gibbs free energy of the system; A=surface
area; T=temperature; P=pressure; and N=composition.
[0026] "Contact angle" refers to the angle between the plane of the
solid surface and the tangential line to the liquid boundary
originating at the point of three phase contact
(solid/liquid/vapor).
[0027] "Strip" refers to a long narrow piece of a material that is
substantially flat or planar.
[0028] "Plate" refers to a thin piece of material that is
substantially flat or planar, and it can be in any suitable shape
(e.g., rectangular, square, oblong, circular, etc.).
[0029] "Substantially flat" refers to a substrate having the major
surfaces essentially parallel and distinctly greater than the minor
surfaces (e.g., a strip or a plate).
[0030] "Electrically conducting" refers a material that is capable
of transmitting electricity or electrons.
[0031] "Adsorbent" refers to a material comprising binding
functionalities that adsorb analytes.
[0032] "Binding functionalities" refer to functional group(s) of
that bind analytes. Binding functionalities can include, but are
not limited to, a carboxyl group, a sulfonate group, a phosphate
group, an ammonium group, a hydrophilic group, a hydrophobic group,
a reactive group, a metal chelating group, a thioether group, a
biotin group, a boronate group, a dye group, a cholesterol group,
derivatives thereof, or any combinations thereof. Binding
functionalities can further include other functionalities that can
bind analytes based on individual structural properties, such as
the interaction of antibodies with antigens, enzymes with substrate
analogs, nucleic acids with binding proteins, and hormones with
receptors.
[0033] "Analyte" refers to a component of a sample which is
desirably detected. The term can refer to a single component or a
set of components in the sample.
[0034] "Adsorb" refers to the detectable binding between binding
functionalities and an analyte either before or after washing with
an eluant (selectivity threshold modifier).
[0035] "Resolve," "resolution," or "resolution of analyte" refers
to the detection of at least one analyte in a sample. Resolution
includes the detection of a plurality of analytes in a sample by
separation and subsequent differential detection. Resolution does
not require the complete separation of an analyte from all other
analytes in a mixture. Rather, any separation that allows the
distinction between at least two analytes suffices.
[0036] "Detect" refers to identifying the presence, absence or
amount of the object to be detected.
[0037] "Energy absorbing molecule" or "EAM" refers to a molecule
that absorbs energy from an energy source in a mass spectrometer
thereby enabling desorption of analyte from a probe surface. Energy
absorbing molecules used in MALDI are frequently referred to as
"matrix." Cinnamic acid derivatives, sinapinic acid and
dihydroxybenzoic acid are frequently used as energy absorbing
molecules in laser desorption of bioorgainc molecules. See U.S.
Pat. No. 5,719,060 (Hutchens & Yip) for additional description
of energy absorbing molecules.
[0038] II. Probes
[0039] This invention provides probes that are removably insertable
into a mass spectrometer. The probes comprise a substrate having a
surface and a film that coats the surface and comprises openings
that expose the surface. The film has a water contact angle of
between 120.degree. and 180.degree.. The film also has lower
surface tension than the substrate surface, so that liquid applied
to the exposed areas tend to be sequestered in those areas. In
certain embodiments the coatings of this invention are
significantly more hydrophobic than coatings that can be applied
manually.
[0040] A. Substrate
[0041] The substrate can be made from any suitable material that is
capable of supporting a film and the sample. For example, the
substrate material can include, but is not limited to, glass,
ceramic (e.g., titanium oxide, silicon oxide), organic polymers,
metals (e.g., nickel, brass, steel, aluminum, gold), paper, a
composite of metal and polymers, or combinations thereof.
[0042] The substrate can have various properties. The substrates
generally are non-porous, e.g., solid, and substantially rigid to
provide structural stability. Furthermore, the substrate can be
electrically insulating or conducting. In a preferred embodiment,
the substrate is electrically conducting to reduce surface charge
and to improve mass resolution. Electrical conductivity can be
achieved by using materials, such as electrically conductive
polymers (e.g., carbonized polyetheretherketone, polyacetylenes,
polyphenylenes, polypyrroles, polyanilines, polythiophenes, etc.),
or conductive particulate fillers (e.g., carbon black, metallic
powders, conductive polymer particulates, fiberglass-filled
plastics/polymers, elastomers, etc.).
[0043] The substrate can be in any shape as long as it allows the
probe to be removably insertable into a mass spectrometer. In one
embodiment, the substrate is substantially flat and substantially
rigid. Typically, a probe can take the shape of a rod, wherein a
surface at one end of the rod is the sample presenting surface, a
strip or a rectangular or circular plate. Furthermore, the
substrate can have a thickness of between about 0.1 mm to about 10
cm or more, preferably between about 0.5 mm to about 1 cm or more,
most preferably between about 0.8 mm and about 0.5 cm or more.
Preferably, the substrate itself is large enough so that it is
capable being hand-held. For example, the longest cross dimension
of the substrate can be at least about 1 cm or more, preferably
about 2 cm or more, most preferably at least about 5 cm or
more.
[0044] Typically, the probe is adapted for use with inlet ports and
detectors of a mass spectrometer. For example, the probe can be
adapted for mounting in a horizontally and/or vertically
translatable carriage that horizontally and/or vertically moves the
probe to a successive position. Such a carriage provides a
plurality of features on a probe to be in the path of an energy
beam, thereby allowing detection of analytes without requiring
repositioning of the probe.
[0045] In a preferred embodiment, the probes of this invention are
adapted for SELDI. Accordingly, the areas of the surfaces that will
form the features can have adsorbents attached that will
selectively bind analytes. The adsorbents can he highly specific
for an analyte, such as antibodies, or they can be relatively
unspecific, such as anion or cation exchange resins. Alternatively,
the surface can have energy absorbing molecules or photolabile
attachment groups attached. For examples of each see U.S. Pat. No.
5,719,060 (Hutchens & Yip) and WO 98/59361 (Hutchens &
Yip).
[0046] B. Film
[0047] The substrate of the probe of this invention is coated with
a film. The purpose of the film is two-fold. First, the film
defines the locations where sample is to be placed, also called
features. Second, because it has a high water contact angle and
less surface tension than the probe surface, the film provides a
barrier against the overflow of liquid sample placed on the
features.
[0048] In order for the film to sequester the liquid sample, it
should have less surface tension than the surface of the probe.
Generally, the sample will be an aqueous solution. In this case, to
perform its function, the film will be hydrophobic. However, this
invention contemplates other liquid samples, as well. In this case,
the film will be made of a material that does not dissolve in the
liquid of the sample. Best results also are obtained when the film
has a water contact angle of at least 120.degree. and 180.degree..
Most preferably, the water contact angle is greater than
160.degree..
[0049] The film has a thickness on the probe surface of between 1
angstrom and 1 mm. Preferably, the thickness is between 1 micron
and 1000 microns (1 mm.) Most preferably, the film has a thickness
of between about 10 microns and 500 microns. A thickness of around
100 microns is particularly useful.
[0050] The film coats the surface of the probe in such a way as to
leave at least one opening or lacuna in the coating that exposes
the surface of the probe. The opening defines a feature where the
sample will be applied. Thus, while the film need not coat the
entire surface of the probe, it should encircle the opening with
sufficient width as to carry out the function of providing a
barrier to the spilling over of liquid. Generally, the band of film
that encircles the lacuna will be at least 0.3 mm wide and more
preferably, at least 1.5 mm wide.
[0051] More generally, the film will form a continuous coating over
a substantial surface of the probe with a plurality of openings
placed throughout the continuous surface. The features preferably
are arranged in an orderly fashion, such as a linear, rectangular
or circular array for easy addressability.
[0052] When the probe is adapted for the surface-enhanced affinity
capture version of SELDI, the film generally will surround the
features that have the affinity materials attached. Thus, the film
acts as a hydrophobic sea surrounding an island of affinity
materials.
[0053] The film preferably comprises a polymer. For example, the
polymer can be selected from perfluorinated hydrocarbons,
halogenated hydrocarbons, aliphatic hydrocarbons, aromatic
hydrocarbons, polysilanes, organosilanes and combinations thereof.
One commercial source for polymer coatings is Cytonix, Beltsville,
Md., USA. In other embodiments, the film is a molecular organic
material (e.g., a Langmuir-Blodgett film or a self-assembling
mono-layer, e.g., a decane thiol on gold).
[0054] The polymer preferably is a perfluorinated polymer.
Exemplary fluorinated polymers include poly(hexafluoropropylene);
poly(tetrafluoroethylene) (e.g., Teflon.RTM.);
poly(trifluoroethylene); poly(vinyl fluoride); poly(vinylidene
fluoride); poly((heptafluoroisoprop- oxy)ethylene);
poly(1-((heptafluoroisopropoxy)methyl) propylene-stat-maleic acid);
poly(1-heptafluoroisopropoxy)propylene);
poly((1-chlorodiflyoromethyl)tetrafluoroethyl acrylate);
poly(di(chlorodifluoromethyl) fluoromethyl acrylate);
poly(1,1-dihydroheptafluorobutyl acrylate);
poly(heptafluoroisopropyl acrylate);
poly(2-(heptafluoropropoxy)ethyl acrylate); poly(nonafluoroisobutyl
acrylate), and poly(t-nonafluorobutyl methacrylate). One useful
fluorinated polymer is described in U.S. Pat. No. 5,853,891
(Brown).
[0055] Exemplary halogenated polymers include
poly(chlortrifluoroethylene)- ; poly(vinyl chloride); and
poly(vinylidene chloride).
[0056] Exemplary aliphatic polymers include poly(isobutene);
poly(ethylene), poly(isoprene); poly(4-methyl-1-pentene);
poly(vinyl butyrate); poly(vinyl dodecanoate); poly(vinyl
hexadecanoate); poly(vinyl propionate); poly(vinyl octanoate);
poly(methacrylonitrile); poly(vinyl alcohol); and poly(vinyl
butyral).
[0057] Exemplary epoxy resins include diglycidyl ether of
bisphenol-A, 2,3-di(glycidoxy-1,4-phenylene)propane; and diglycidyl
ether of bisphenol-A with 0.5% of
g-glycidoxypropyltrimethoxy-silane cured with
g-glycidoxyproplytrimethoxysilane.
[0058] Exemplary aromatic polymers include poly(styrene);
poly(2-methyl styrene), poly(xylelene) and phenol-formaldehyde
resins such as novolac.
[0059] Exemplary polysilanes and organosilanes include
poly(oxydiethylsilylene); poly(oxydimehtylsilylene);
poly(oxymethylphenylsilylene), condensed methyltrimethoxysilane and
condensed g-aminopropyltirethoxysilanes.
[0060] The deposition of such polymers is described in, for
example, Characterization of Organic Thin Films; Ulman, A., Ed.;
Manning: Greenwich, 1995 (ISBN 0-7506-9467-X) and Polymer Handbook,
3.sup.rd edition; Brandrup, J. and Immergut, E. H., Eds.; John
Wiley & Sons: New York, 1989 (ISBN 0-471-81244-7).
[0061] The surface tension of the polymer generally will be less
than 40, preferably less than 30, more preferably less than 20. The
surface tension of the polymer can be increased by making it
microporous. Microporous films have holes of about 5 microns in
size.
[0062] Films can be applied to substrates by any method known in
the art including for example screen printing, electrospray, ink
jet , vapor or plasma deposition or spin coating. To create the
features, a lithographic process can be used. This can be done by
masking the area prior to deposition or by removing deposited
material by etching or burning with an electron, a laser or an ion
beam process, or employing a more sophisticated photolithographic
process.
[0063] III. Methods of Detection
[0064] The probes of this invention are useful in the detection of
analytes placed on the features of the probe. In these methods, the
probes are used in connection with a gas phase ion spectrometer.
This includes, e.g., mass spectrometers, ion mobility spectrometers
or total ion current measuring devices.
[0065] In one embodiment, a mass spectrometer is used with the
probe of the present invention. A sample placed on the feature of
the probe of the present invention is introduced into an inlet
system of the mass spectrometer. The sample is then ionized by an
ionization source. Typical ionization sources include, e.g., laser,
fast atom bombardment, or plasma. The generated ions are collected
by an ion optic assembly, and then a mass analyzer disperses and
analyzes the passing ions. The ions exiting the mass analyzer are
detected by a detector. The detector then translates information of
the detected ions into mass-to-charge ratios. Detection of an
analyte will typically involve detection of signal intensity. This,
in turn, reflects the quantity of analyte bound to the probe. For
additional information regarding mass spectrometers, see, e.g.,
Principles of Instrumental Analysis, 3.sup.rd ed., Skoog, Saunders
College Publishing, Philadelphia, 1985; and Kirk-Othmer
Encyclopedia of Chemical Technology, 4.sup.th ed. Vol. 15 (John
Wiley & Sons, New York 1995), pp. 1071-1094.
[0066] In a preferred embodiment, a laser desorption time-of-flight
mass spectrometer is used with the probe of the present invention.
In laser desorption mass spectrometry, a sample on the probe is
introduced into an inlet system. The sample is desorbed and ionized
into the gas phase by laser from the ionization source. The ions
generated are collected by an ion optic assembly, and then in a
time-of-flight mass analyzer, ions are accelerated through a short
high voltage field and let drift into a high vacuum chamber. At the
far end of the high vacuum chamber, the accelerated ions strike a
sensitive detector surface at a different time. Since the
time-of-flight is a function of the mass of the ions, the elapsed
time between ionization and impact can be used to identify the
presence or absence of molecules of specific mass. As any person
skilled in the art understands, any of these components of the
laser desorption time-of-flight mass spectrometer can be combined
with other components described herein in the assembly of mass
spectrometer that employs various means of desorption,
acceleration, detection, measurement of time, etc.
[0067] Furthermore, an ion mobility spectrometer can be used to
analyze samples. The principle of ion mobility spectrometry is
based on different mobility of ions. Specifically, ions of a sample
produced by ionization move at different rates, due to their
difference in, e.g., mass, charge, or shape, through a tube under
the influence of an electric field. The ions (typically in the form
of a current) are registered at the detector which can then be used
to identify the sample. One advantage of ion mobility spectrometry
is that it can operate at atmospheric pressure.
[0068] Still further, a total ion current measuring device can be
used to analyze samples. This device can be used when the probe has
a surface chemistry that allows only a single type of analytes to
be bound. When a single type of analytes is bound on the probe, the
total current generated from the ionized analyte reflects the
nature of the analyte. The total ion current from the analyte can
then be compared to stored total ion current of known compounds.
Therefore, the identity of the analyte bound on the probe can be
determined.
EXAMPLE
[0069] A probe of this invention is constructed as follows. (See
FIG. 1.) An aluminum strip 101 having dimensions 80 mm.times.9
mm.times.25 mm was prepared. Poly(tetrafluoroethylene) was screen
printed on the long surface of a strip to create a film 102. The
film covered virtually the entire surface, except for 8 openings in
the shape of circles (2.4 mm diameter) defining features 103. An
aqueous solution of 3-(methacryloylamino)propyl trimethylammonium
chloride (15 wt %), N,N'-methylenebisacrylamide (0.4 wt %),
(-)-riboflavin (0.01 wt %) and ammonium persulfate (0.2 wt %) was
then deposited onto each opening (0.5 .mu.L per opening). The strip
was then irradiated for 5 minutes with a near UV exposure system
(Hg short arc lamp, 20 mW/cm2 at 365 nm). This functionalities the
probe surface for binding analytes with ammonium functionalities.
After washing the surface once with a solution of sodium chloride
(1M) and twice with deionized water, the probe was ready for
use.
[0070] The present invention provides novel probes for gas phase
ion detectors having films on their surfaces that sequester sample.
While specific examples have been provided, the above description
is illustrative and not restrictive. Many variations of the
invention will become apparent to those skilled in the art upon
review of this specification. The scope of the invention should,
therefore, be determined not with reference to the above
description, but instead should be determined with reference to the
appended claims along with their full scope of equivalents.
[0071] All publications and patent documents cited in this
application are incorporated by reference in their entirety for all
purposes to the same extent as if each individual publication or
patent document were so individually denoted. By their citation of
various references in this document Applicants do not admit that
any particular reference is "prior art" to their invention.
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