Development of a Hybrid Enzyme-Based Porous Silicon Platform for Chemical Warfare Agent Detection
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Development of a Hybrid Enzyme-Based Porous Silicon Platform for Chemical Warfare Agent Detection Sonia E. Létant1, Bradley R. Hart1, Staci R. Kane1, Masood Z. Hadi2, Sharon J. Shields1, Tu-Chen Cheng3, Vipin K. Rastogi3, J. Del Eckels1, and John G. Reynolds*1 1 Forensic Science Center, University of California, Lawrence Livermore National Laboratory, Livermore, CA 94551. 2 Lockheed Martin Corporation, Sandia National Laboratory, Livermore CA, 94551. 3 U. S. Army Edgewood Research, Development, and Engineering Center, Aberdeen, MD 21010. ABSTRACT The goal of our research is to combine porous silicon and enzymes in order to build hybrid platforms for extremely selective chemical sensing applications. For this, a new synthetic route to covalently anchor bio-molecules on photo-luminescent porous silicon (PL PSi) while preserving the optical properties of the matrix was developed. The hydride terminated porous silicon surface was covalently functionalized with tbutyloxycarbonyl protected amine by light-assisted hydrosysilation. Protein cross-linker chemistry was then used to extend the linker and immobilize various enzymes. The glucoronidase enzyme/p-nitro-phenyl-beta-glucoronide substrate test system provided a proof of concept for an enzyme-based porous silicon detector. The enzymatic activity and the luminescence of the porous silicon platform were both retained after the functionalization procedure and, charge transfer between the products of the enzymatic breakdown and the silicon quantum dots was demonstrated. The organophosphorous hydrolase enzyme OPAA was then immobilized and tested on p-nitrophenyl-soman, a surrogate substrate for soman. The production of the hydrolysis product, p-nitrophenol, correlated with the reversible luminescence quenching of the porous silicon matrix demonstrating the relevance of the enzyme-based platform for detection applications. This detection scheme, although indirect, takes advantage of the extreme specificity of enzymes. The approach is general and can be implemented for a series of target molecules. INTRODUCTION The use of chemical detector systems is critical in many applications ranging from counter-terrorism to human health. Although commercial systems are available, development of new detection systems remains required because of the need for broad based monitoring of large varieties of chemical species as well as more specificity and selectivity towards individual highly toxic species. Monitoring ranges from personnel, such as first responders, to facilities, such as airports, subways and office buildings. The chemical threats range from simple industrial chemicals with mild toxicity to complex organophosphorus nerve agents with extreme toxicity. Of the organophosphorus nerve argents, the G agents are of particular focus because of their cholinesterase activity coupled to high volatility. Detection systems for these agents must therefore be highly sensitive and fast. We have been working towards the development of chemical weapons detection
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