E-field induced ion selective molecular deposition onto sensor arrays

A sensor array for sensing at least one of chemical moieties and biological moieties is provided. The sensor array comprises a plurality of working electrodes electrically associated with a reference electrode, each working electrode in combination with the reference electrode forming a transducer. Each working electrode is provided with a coating of a sensing element comprised of an ionizable moiety and a functional group sensitive to one of the chemical and/or biological moieties.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is related to application Ser. No. 11/059,430, filed on even date herewith, the contents of which are incorporated herein by reference, now abandoned. That application relates to a method for integrating a certain array of selected chemical differentiators in conjunction with certain transducers to form a system capable of recognizing a board spectrum of analytes.

TECHNICAL FIELD

The present invention is directed to sensor arrays for detection of various chemical and/or biological species.

BACKGROUND ART

The characterization and quantification of individual chemical and complex biological molecules is extremely important in fields such as medicine, environmental protection, security, military, and other areas. The determination of individual chemical and complex biological molecules is currently complex and generally requires sophisticated and bulky equipment.

Even though many commercial products along with hundreds of patents have been filed in chemical and biological sensor field, sensor technologies to date are generally used to detect a single type or very few different types of molecules. None of them are particularly adapted to allow a very large number of different types of chemical or biological molecules to be detected.

In order to develop a highly selective, highly sensitive, and universal sensor system, a micro- or nano-sensor array with multiple different sensing elements, each connected to its own specific transducer, has been regarded as one of the possible ultimate solutions. Sensor arrays offer several advantages over single sensors. For example, sensor arrays have better sensitivity to a wider range of analytes. Such arrays offer better selectivity, multi-component analysis, and analyte recognition, rather than mere detection. Sensor arrays are more analogous to olfaction systems containing multiple receptors, whose responses are interpreted by neuron odor recognition processes.

Many existing technologies can be used to build a normal or mini scale of sensor arrays with multiple different sensing elements; examples of such technologies include e-beam lithography, selective thermo deposition, etc. However, none of the above-mentioned technologies work well in the micro- or nano-region. Selectively introducing different types of sensing elements onto different transducers in the micro- or nano-region and providing the micro- or nano-sensor array with multiple different sensing elements have been under active investigation. However, actually achieving these goals has been a challenge, due to the difficulties associated with how to selectively introduce different types of sensing elements onto different transducers in the micro- or nano-region.

Thus, there is a need for different types of sensing elements on different transducers, as well as sensor arrays with multiple different sensing elements, both in the micro- and nano-regimes.

DISCLOSURE OF INVENTION

A sensor array for sensing at least one of chemical moieties and biological moieties is provided. The sensor array comprises a plurality of working electrodes electrically associated with a reference electrode, each working electrode in combination with the reference electrode forming a transducer. Each working electrode is provided with a coating of a sensing element comprised of an ionizable moiety and a functional group sensitive to one of the chemical and biological moieties.

A method of forming the sensor array is provided. The method comprises:providing a plurality of working electrodes;providing a reference electrode electrically associated with the plurality of working electrodes, each working electrode in combination with the reference electrode forming a transducer; andproviding each working electrode provided with a coating of a sensing element comprised of an ionizable moiety and a functional group sensitive to one of the chemical and biological moieties.

A method of sensing at least one of chemical moieties and biological moieties is provided. The method comprises:providing a sensor array, said sensor array comprising a plurality of working electrodes electrically associated with a reference electrode, each working electrode in combination with said reference electrode forming a transducer, each working electrode provided with a coating of a sensing element comprised of an ionizable moiety and a functional group sensitive to at least one said chemical and biological moiety;exposing said sensor array to at least one chemical moiety or biological moiety or both; anddetecting a signal corresponding to a sensed chemical moiety or biological moiety or both.

BEST MODES FOR CARRYING OUT THE INVENTION

Reference is made now in detail to specific embodiments, which illustrates the best mode presently contemplated by the inventors for practicing the invention. Alternative embodiments are also briefly described as applicable.

As used herein, the term “micro-regime” refers to 0.5 μm and above.

As used herein, the term “nano-regime” refers to 1 to 100 nm.

In accordance with the teachings herein, an electric field (E-field) directed ion-selective molecular deposition process is provided. Basically, different sensing elements are introduced selectively onto different transducers (whether through chemical bonding or physical adsorptions) by selectively activating the particular transducer (electrode) in an array and deactivating the rest of the transducers. The activation is achieved by manipulation of the electric field among the array of the transducers (electrodes). The sensing elements are provided with an ionizable connecting group. This is done by pre-ionizing each particular type of sensing element, and then introducing the sensing element into the system containing one or more selectively activated micro- or nano-transducer(s) in the array.

Examples of methods for pre-ionization include, but are not limited to, electrospray and chemical ionization. The former pre-ionization method has been used in mass-spectrometer instruments. The van der Waals interaction between the pre-ionized sensing elements and the E-field system in the array will direct the ion-selective deposition very precisely and highly selectively. The positive potential on the activated electrode will attract the negatively charged sensing elements onto its (or their) surface and promote chemical bonding reaction between them. The negative potential on those deactivated transducers (electrode) in the system will repel those anionic sensing elements away from their surface and protect themselves from unwanted deposition. Through this type of sequential activation and deposition process, a micro- or nano-sensor array with multiple different sensing elements, each connected to its own specific transducer, is easily achieved.

FIGS. 1-5offer a schematic overview of the principles and design characteristics of how this process works with a generic example, while a schematic overview on a more specific example with actual chemical functional groups is given inFIGS. 6-9. It is worth noting that all of the examples described below use nucleophilic anions (Nu−) as the preferred method to covalently link the sensing elements to the transducer surface. However, other linking means are possible even though they are not explicitly given here. For example, one might use electrophilic cations (E+) to link in either covalent bonding or ionic bonding to the surface of an activated transducer, and the activated transducer should have a negative potential and the deactivated working electrode will have the positive potential in this situation.

All the examples herein are only illustrative of the preferred embodiment, which achieves the objects, features and advantages of present teachings, and it is not intended that the present teachings be limited thereto.

The following legends and explanatory notes apply toFIGS. 1-5:The symbol Nu−is an abbreviation for an anionic nucleophilic terminating group, which is capable of self-assembly onto the selected solid substrate (transducer). It is generated chemically or electrochemically from an anionic functional group. It is worth noting that those anionic functional groups used here should be chemically inert or have very low reactivity towards the surface of transducers, but at the same time, their anionic forms should be highly reactive and much more reactive than other type of anions existed in the system. The Nu−can be, but is not limited to, one of the following: —S−, —O−, —NH−, —N(alkyl)−, —N(aryl)−, N(acyl)−, —COO−, etc.FG1, FG2, FG3, FG4, FG5, FG6, FG7, and FG8are abbreviations for different sensing functional end-groups. They can be the same or different. Those functional groups can be either neutral or ionizable during the pre-ionization process. However, these sensing functional end-groups should not interfere or compete with Nu−during the E-field directed ion selective molecular deposition process. On the contrary, these sensing functional end-groups should form certain linkages easily with the molecules to be detected after the sensor system is activated. The sensing functional end-groups can be, but are not limited to, any one of the following: SH, OH, NH2, NH-alkyl, NH-aryl, NH-acyl, unsaturated hydrocarbon or substituted hydrocarbon, heterocyclic systems, carboxylic acid or its derivatives (e.g., ester or amide, etc.), sulfuric acid or its derivatives (e.g., ester or amide, etc.), and phosphoric acid or its derivatives (e.g., ester or amide, etc.). It is worth noticing that even though only FG1, FG2, FG3, FG4, FG5, FG6, FG7, and FG8are given here, more or fewer of other types of sensing elements can be used, depending on the specific application (e.g., using a specific enzyme, protein, bioactive or biospecific molecule, combination of certain chromophore or fluorophore with the sensing molecule to detect the fluorescent change or color change, etc.).

The working electrodes here represent different types of E-field activatable transducers in the array. They are made of a single metal, metal alloy, metal oxide, organic-semiconducting material, or inorganic-semiconducting material, etc. The working electrodes are designed in such way that at least one of their surfaces has certain properties and can form some kind of strong linkage with Nu−. The linkage between Nu−and working electrodes can be either a chemical bonding or a physical adsorption, even though covalent linkage of the sensing elements to the transducer surface is preferred here. A special surface treatment of the working electrode may be needed in order to form a good covalent linkage with the sensing elements. For example, one can either (a) coat a thin layer of novel metal (e.g., Pt, Au, Ag, Cu, etc.) on the top of the working electrode, which can form a strong covalent bond with —S−or —NH−, etc.; or (b) cauterize and halogenate of the surface of SiO2, in which case, the resulting Si—X (X═Cl, Br, I) functional group on the surface of the working electrode will be highly reactive with many anionic nucleophiles to form a strong covalent bond through a nucleophilic substitution.

The reference electrode depicted in the Figures is a supporting electrode. It is chemically inert toward the anionic nucleophiles. The function of the reference electrode here is to form electrode pairs with at least some of the working electrodes and provide an adequate E-field with them. It helps to deactivate those working electrodes during a sequential E-field directing molecular deposition process and prevents them from unwanted molecular deposition during the selective deposition process.

It is worth noting that more or less of other type of anions usually exist in the system, depending on which method is used to generate the anionic sensing element(s). The solvent and the reagent used in this process (usually a stronger base in the chemical ionization process) must be carefully selected in order to ensure a smooth and quantitative generation of the anion of the sensing elements without introducing other types of anions in the system. In the case that there might be still trace amount of other anions in the system due to certain processes, for example, some excess reagent remaining from the chemical ionization reaction, the reagent should be chosen with a desired property that it is a strong base and poor nucleophile, so that it can deprotonate the sensing element easily and react with the surface of transducer much slowly.

FIG. 1depicts a structure comprising an array10of transducers12. The transducers comprise a plurality of working electrodes14electrically associated with a reference electrode16.

As depicted inFIG. 2, only one of the working electrodes,14a, along with the reference electrode16, is activated by applying a positive potential on both the selected working electrode and the reference electrode, while the rest of the working electrodes14in the array10are deactivated by applying a negative potential on them at the same time.

As depicted inFIG. 3, a first type of sensing element18, comprising a nucleophilic moiety Nu−20and a functional group FG122is provided. The sensing element initially comprises a moiety that is anionizable to nucleophilic moiety plus the functional group. The anionizable moiety is then anionized chemically or electrochemically, and the sensing element is introduced into the system10with only one activated working electrode14a. The positive potential on the activated working electrode14aattracts the negatively charged sensing elements18onto its surface and form a covalent linkage with them through nucleophilic substitution. The negative potential on those deactivated electrodes14in the array10drives the anionized sensing elements18away from their surface with the help of the reference electrode16, and protects them from unwanted deposition. This process is very selective and essentially no undesired molecular deposition takes place. A post-cleaning step is used to avoid cross-contamination and make the system ready for next type of molecular deposition. The so-called post-cleaning step is intended to sweep out those loosely attached ionic molecular species from the surface of the reference electrode16by using certain appropriate media (solvent or gas) or vacuum while temporarily removing the potential on the reference electrode16. In this way, the excess reagents from previous deposition processes are removed and cross-contamination to the next sensor element deposition is avoided.

As depicted inFIG. 4, a second type of sensing element118is deposited selectively onto a second working electrode14bby the four-step process of selective activation of the second electrode, pre-ionization of the second type of sensing elements, E-field directed deposition, and post-cleaning. The sensing element118comprises a nucleophilic moiety Nu−120and a functional group FG2122.

As depicted inFIG. 5, by repeating the four-steps process (selective activation of a working electrode14, pre-anionization of another type of sensing element, E-field directed deposition, and post-cleaning) sequentially on the different working electrodes to provide a sequence of electrodes14a. . .14h, different types of sensing elements can be deposited very selectively onto different working electrodes (transducers) in the array10.

A more specific example of E-field directed ion selective molecular deposition with actual chemical functional groups is given inFIGS. 6-9.

In this particular example, S−is chosen as a preferred anionic nucleophile20. The alkyl amine, carboxylic acid, aryl amine, phenol, amide, OH, aromatic or aliphatic ending groups are chosen here as desired sensing groups22. It is worth noticing that even though the examples described here use —NR2, —COOH, —CONH2, —Ar—NH2, —ArOH, —Ar, —R, —OH, etc. as preferred sensing groups, other type means are possible even though they are not explicitly given here. All the examples are only illustrative of the preferred embodiment, which achieves the objects, features and advantages of present teachings, and it is not intended that the present teachings be limited thereto.

In this particular example, the surface of working electrodes14can either be made of noble metal (such as Au, Pt, Ag, Cu, etc.) or Si—Cl (if using a Si electrode). Other materials useful for working electrodes include, but are not limited to, GaAs, InP, In2O3, and ZnO. The reference electrode16can be made of any material that is chemically inert material to S−; examples include, but are not limited to, Si, C, TiN, ITO (indium tin oxide), and ZnO. If a different anionic nucleophile is used in place of S−, then the reference electrode16would comprise a material inert to that different anionic nucleophile. The determination of a suitable reference electrode material is readily within the ability of the person skilled in the art, and would require no undue experimentation.

At first, a desired array of working electrodes14and reference electrode16are prepared, and pretreated to possess certain desired chemical properties (which can form a covalent linkage with S−through chemical reaction). Then, one of the working electrodes14ais selectively activated by applying a positive potential on it and deactivating the other working electrodes in the array10with a negative potential, as described above with reference toFIG. 1.

As depicted inFIG. 6, the thiol group20of amine-terminated (—NR2) sensing elements18′ is first pre-anionized chemically or electrochemically to strip off the hydrogen atom from the thiol group (—SH), leaving S−. Then the ionized sensing element18is introduced into the system with only one activated working electrode14ain the array10. The positive potential on the activated working electrode14aattracts the negatively charged sensing elements18onto its surface and forms a covalent linkage with them through nucleophilic substitution. The negative potential on those deactivated electrodes14in the array10drives the anionized sensing elements18away from their surface with help from the reference electrode16, and protects them from unwanted deposition. This process is very selective and essentially no undesired molecular deposition takes place. A post-cleaning step is necessary to avoid cross-contamination and make the system ready for next type of molecular deposition. The so-called post-cleaning step is to sweep out those loosely attached ionic molecular species from the surface of reference electrode by using certain proper media (solvent or gas) or vacuum while temporarily removing the potential on the reference electrode.

In the amine, R is an atom or functional group. It can be a hydrogen atom or an alkyl group. A methyl or ethyl group is preferred in some embodiments. The two R moieties may be the same or different.

As depicted inFIG. 7, a second type of sensing element118is a dual functional molecule with carboxylic acid functional end-group122′ and thiol (—SH) group120′. The sensing element118is deposited selectively onto a second working electrode14bby a four-steps process (selective activation of the second electrode, pre-ionization of the second type of sensing element, E-field directed deposition, and post-cleaning). Under chemical anionization, —COOH is anionized to form —COONa122, and the —SH is anionized also to form —SNa (S−) 120 for example, by NaOH treatment. In the case of using a silicon electrode14b, even though both its carboxylic acid (—COOH) and thiol (—SH) group can be anionized at the same time under the reaction condition, however the nucleophilicity of the —S−portion of the resulting anionized specie is much stronger than its —COO−portion and consequently, the rate of nucleophilic substitution of Cl at the Si—Cl site with S−anion is 3 to 4 orders faster than the corresponding —COO−anion. This results in exclusively an —S—Si moiety bonded to the bottom electrode, while the anionized carboxylic acid functional end-group remains unbonded. The desired S-attachment is the dominant product from the process. In the case of using noble metal electrodes14, only the S−can react with the noble metal to form a strong covalent linkage, and the —COO−group is totally inert in this situation.

As depicted inFIG. 8, by repeating the four-steps process (selective activation of the next electrode, pre-anionization of the next type of sensing element, E-field directed deposition, and post-cleaning) sequentially on the different working electrodes, various types of sensing elements can be deposited very precisely and selectively onto different working electrodes (transducers) in an array.

Since the —COONa group may not be a good sensing group in some instances, it may be necessary to convert the —COONa group to the corresponding —COOH group by a two-steps post-treatment process (acidification followed by heat treatment) to activate the sensor system, as shown inFIG. 9, at electrode14b.

It can be seen from the Table below that each specific sensing element can detect a range of molecular functional groups based on their specific oriented chemical or physical interactions. However, different functional groups will usually interact with a unique sub-set of the sensing elements in the sensor array. While eight sensing elements are shown in the Figures, it will be appreciated that more or less than that number may be actually employed in a working device. This characteristic signature when combined with the knowledge of its molecular backbone and molecular mass will enable identification of the analyte in most cases. While chemical moieties are specifically disclosed, it will be appreciated that the techniques disclosed herein of electric field induced selective deposition of sensor arrays can be used for biomolecular sensor arrays as well.

The current teachings provide a simple solution on how to selectively introduce different types of sensing elements onto different transducers in the micro- or nano-region. The teachings permit construction of a micro- or nano-sensor array of multiple different sensing elements.

The teachings disclosed herein permit building a highly selective and universal micro- or nano-sensing system, which will allow a very large number of different types of chemical or biological molecules to be detected in a simple, fast, and cost effective way.

INDUSTRIAL APPLICABILITY

The sensor array is expected to find use in detecting various chemical and/or biological species.