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Gold thiolate and photochemically functionalized microcantilevers using molecular recognition agentsRelated Patent Categories: Chemical Apparatus And Process Disinfecting, Deodorizing, Preserving, Or Sterilizing, Analyzer, Structured Indicator, Or Manipulative Laboratory Device, Means For Analyzing Gas Sample, Including Means For Adsorbing Or Absorbing Gas Into Or Onto Liquid Or Solid MediaGold thiolate and photochemically functionalized microcantilevers using molecular recognition agents description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060057026, Gold thiolate and photochemically functionalized microcantilevers using molecular recognition agents. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims priority to U.S. Provisional Patent Application 60/609,610 filed Sep. 14, 2004, and is related to U.S. patent application Ser. No. 11/059,170, filed Feb. 16, 2005, both herein incorporated by reference. FIELD OF THE INVENTION [0003] This invention relates to highly sensitive sensor platforms for the detection of specific reagents, such as chromate, gasoline and biological species, using microcantilevers and other microelectromechanical systems (MEMS) whose surfaces have been modified with photochemically attached organic monolayers, such as self-assembled monolayers (SAM), or gold-thiol surface linkage. The microcantilever sensors use photochemical hydrosilylation to modify silicon surfaces and gold-thiol chemistry to modify metallic surfaces thereby enabling individual microcantilevers in multicantilever array chips to be modified separately. By focusing the activating UV light sequentially on selected silicon or silicon nitride hydrogen terminated surfaces and soaking or spotting selected metallic surfaces with organic thiols, sulfides, or disulfides, the microcantilevers are functionalized. The device and photochemical method are intended to be integrated into systems for detecting specific agents including chromate groundwater contamination, gasoline, and biological species. BACKGROUND OF THE INVENTION [0004] Micro-electro-mechanical systems (MEMS) are likely candidates for extremely sensitive, inexpensive sensors, which can be mass produced. Microcantilever sensors offer much better sensitivities compared to other MEMS sensors and have surface areas of the order 10.sup.-4 cm.sup.2, which is smaller than that of other miniature devices (such as Surface Acoustic Wave devices, SAW) by orders of magnitude. They can be mass produced at relatively low cost using standard semiconductor manufacturing processes and have demonstrated superior detection sensitivities for physical, chemical and biological sensing. Microcantilever-based sensors have been shown to be extremely sensitive; however silicon or silicon nitride microcantilevers coated on one surface with gold do not have any particular chemical selectivity. Chemical selectivity has been achieved by coating the gold surface of the microcantilevers with a selective film such as a self-assembled monolayer (SAM) of an alkane thiol having a head group suitable for molecular recognition. Also, functionalized films can be attached to hydrogen terminated silicon and silicon nitride surfaces by photochemical hydrosilylation to achieve more stable coatings. The main feature distinguishing microcantilevers from other MEMS is their unique bending response. They have a high surface-to-volume ratio, and therefore changes in the Gibbs surface free energy induced by surface-analyte interactions lead to large surface forces. When such interactions are restricted to one surface, then the resulting differential stress leads to bending of the cantilever. This bending detection mode can be used in liquid phase, as well as in gas phase, which makes cantilever sensors suitable for both molecular and ionic analytes if selective adsorption can be achieved on one of their surfaces using analyte-specific surface functionalities. A preferred approach to the design of selective sensors is to immobilize agents for selective molecular recognition in a matrix that mimics the organic medium in a solvent extraction system. In this manner, the matrix can enhance both the separation and the achievement of chemical selectivity. The transduction part of the microcantilever sensor is based on binding the molecular recognition agent to one surface of the cantilever so that the adsorption-induced stress change can be detected via bending of the microcantilever. [0005] A problem exists with the formation of SAM coatings on gold coated cantilevers if an array of cantilevers is used. It is difficult to apply a coating, especially if a long period of time is required for a tightly packed layer to form, to a single cantilever in an array without contaminating other cantilevers in the array. Other approaches to modifying a single surface of a silicon cantilever involve reaction of silane reagents with the Si--OH groups on the surface, but again it is problematic to modify only a single cantilever in an array. The photoactivation method of this invention provides a solution to this problem wherein cantilevers are only activated to react with an ethylene substituted hydrocarbon when irradiated with UV light. [0006] Arrays of cantilevers can be conveniently prepared with each cantilever or group of cantilevers having a separate molecular recognition agent to impart chemical selectivity. Attachment of molecular recognition agents to the surface with robust Si--C bonds gives a layer with superior stability. For example, chromium(VI) or chromate can be selectively detected by the microcantilever of this invention. [0007] Chromium is naturally occurring in several different oxidation states. The most frequently encountered forms are the III and VI oxidation states. Chromium(III) is an essential trace element in the human body and plays an important role in the metabolism of glucose, lipids, and proteins. In contrast, Cr(VI) in the form of chromate (CrO.sub.4.sup.2-) is considered to be toxic to animals and humans. Most of the methods used to determine CrO.sub.4.sup.2- (such as ion exchange, chromatography, and atomic absorption spectroscopy) are generally time-consuming, have less than desired accuracy, or are expensive. [0008] In addition, Cr(VI) is more soluble in groundwater than Cr(III), and thus has a greater potential of affecting human health and the environment. Various techniques have been tested for the direct determination of Cr(VI) in water, but most techniques are not suitable due to insufficient detection limits and/or matrix interferences. The method that is widely being used at present requires selective reaction of Cr(VI) with 1,5-diphenylcarbohydrazide followed by spectrophotometry. The commercial sensor technique based on the above method and used widely for Cr(VI) monitoring, has a detection limit of .apprxeq.1.9.times.10.sup.-7 M, close to the current EPA regulation level of 2.1.times.10.sup.-7 M. However, this method is not viable for remote monitoring, and also would not be applicable if federal/local regulated levels are tightened. Therefore, developing inexpensive, easily deployable techniques with higher sensitivity is important for environmental monitoring and remediation. Due to the possibility of mass deployment at low cost, microelectromechanical systems (MEMS), especially microcantilevers, have attracted attention recently due to their high sensitivity of detection. BRIEF DESCRIPTION OF THE INVENTION [0009] Photochemical hydrosilylation of 11-undecenyltriethylammonium bromide with hydrogen-terminated silicon microcantilever surfaces yielded a robust quaternary ammonium terminated organic monolayer that is suitable for chromate detection. Terminal vinyl substituted hydrocarbons with a variety of molecular recognition sites can be attached to the surface of silicon via the photochemical hydrosilylation process. Since the chemicals only react at the surface of Si when irradiated it allows an array of cantilevers to be sequentially modified by exposing an array to the derivatization agent but only activating one or a select group of cantilevers before changing the solution and activating a different cantilever of group of cantilevers. Another embodiment of this invention enables the detection of hexavalent chromium, Cr(VI), in ground water using at least one microcantilever coated with a self-assembled monolayer of 4-mercaptopyridine. The microcantilever sensors use gold-thiol attachment approach for 4-mercaptopyridine (4-MPy) and photochemical hydrosilylation for grafting 11-undecenyltriethylammonium bromide or vinyl pyridine to modify the microcantilever surface for chromate sensing. [0010] One embodiment of the device and method enables the detection of hexavalent chromium, Cr(VI), in ground water using a single microcantilever sensor coated with a self-assembled monolayer of 4-mercaptopyridine. The experiments showed that CrO.sub.4.sup.2- ions can be detected with the microcantilever sensor in the presence of significant concentrations (>1000 pg/l) of Ca.sup.2+, Cl.sup.-, Mg.sup.2+, NO.sub.3.sup.-, K.sup.+, Na.sup.+, and SO.sub.4.sup.2- ions and a variety of other ions of smaller concentrations. The chromate concentrations were also measured using the Hach spectrophotometric kit, which is widely used for chromate monitoring. The cantilever measurements are an order of magnitude more sensitive compared to the spectrophotometric method currently in use, and are amenable for remote detection. [0011] The microcantilever sensor uses gold-thiol or photochemical hydrosilylation to modify the microcantilever surface. The photochemical process enables individual microcantilevers in multicantilever array chips to be modified separately by focusing the activating UV light sequentially on each particular cantilever. Grafting of selected gold coated microcantilevers can be achieved by spotting techniques. The surface functionalities retain their affinity toward Cr(VI), and the organic monolayer is dense enough to generate significant surface stress upon subsequent adsorption of chromate ions from aqueous solutions. BRIEF DESCRIPTION OF THE DRAWINGS [0012] FIGS. 1a and 1b are graphs showing (a) Results of the photometric measurements on the three water samples from the Hanford site. (b) Comparison of the photometric signal from the B173R9 sample with those from standard chromate solutions of concentrations of 2.5.times.10.sup.-7 M and 5.0.times.10.sup.-7 M. [0013] FIGS. 2a and 2b are graphs showing cantilever bending signals of 4-Mpy modified cantilever due to the injections of different amounts of the acidified sample solutions at 10 mL/hr; (a) different amounts of B173R7 and (b) same amount of B173R8 samples. The relative magnitudes of the cantilever bending signals (after normalizing to the injection volumes) are in agreement with the relative concentrations obtained from the photometric measurements. [0014] FIG. 3 is a graph showing cantilever bending signal due to the injection of 2 mL (at pumping speed of 10 mL/hr) of the acidified B173R9 water sample taken from a well at the Hanford site. From historical data for this well, the concentration of hexavalent chromium is expected to be <2.5.times.10.sup.-7 M. The water from this well contains numerous other contaminants, some of which have concentrations exceeding 10.sup.-4 M. [0015] FIG. 4 is the bending response of a gold-coated silicon microcantilever, modified with 11-undecenyltriethylammonium bromide by photochemical hydrosilylation on the silicon side, upon injections of 1 mL of sample chromate solutions: (1) 1.times.10.sup.-4 M CrO.sub.4.sup.2-, left scale; (2) 1.times.10.sup.-9 M CrO.sub.4.sup.2-, right scale. [0016] FIG. 5 shows photochemical hydrosilylation of alkenes and alkynes. Figure taken from Buriak, Chem. Rev. 2002, 102 (5), 1271-1308. [0017] FIG. 6 shows surface structures reported by Buriak, Chem. Rev. 2002, 102 (5), 1271-1308 and Voicu, R., Langmuir, 2004, 20, pp. 11713-11720. [0018] FIG. 7 shows anticipated structure of Si surface modified with quaternary ammonium coating and bonding mode for chromate. It is a schematic representation of a cantilever Si surface functionalized with 11-undecenyltriethylammonium halide using the photochemical hydrosilylation approach for chromate detection. X--.dbd.Br-- immediately following the hydrosilylation process. [0019] FIG. 8 shows photochemical hydrosilylation of 11-undecenyltriethylammonium bromide to hydrogen terminated microcantilevers. [0020] FIG. 9 is a photograph of a typical functionalized microcantilever. Continue reading about Gold thiolate and photochemically functionalized microcantilevers using molecular recognition agents... Full patent description for Gold thiolate and photochemically functionalized microcantilevers using molecular recognition agents Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Gold thiolate and photochemically functionalized microcantilevers using molecular recognition agents patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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