Electrical Porous Silicon Microarray for dna Hybridization Detection
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ELECTRICAL POROUS SILICON MICROARRAY FOR DNA HYBRIDIZATION DETECTION Marie Archer, Marc Christophersen and Philippe M. Fauchet Center for Future Health and Departments of Biomedical Engineering and Electrical & Computer Engineering, University of Rochester, Rochester, NY 14642 Deoram Persaud and Karl D. Hirschman Departments of Microelectronic Engineering and Materials Science & Engineering, Rochester Institute of Technology, Rochester, NY 14623 ABSTRACT The sensitivity of Porous Silicon (PSi) to the presence of charged molecules and its large internal surface area represent two important properties that make this material and ideal candidate for electrical biosensor development. We have demonstrated the use of a macroporous silicon electrical sensor for label-free detection of DNA hybridization in real time as well as identification of organic solvents in liquid phase. Binding of DNA inside the PSi matrix induces a change in capacitance and conductance. Having demonstrated the suitability of macroporous silicon layers for real time detection of DNA hybridization on single devices, we have extended our findings to the fabrication of a microarray with individual device electrical addressing capabilities. On a crystalline ptype silicon wafer, process steps such as KOH etching and electrochemical dissolution are employed in selected regions to create a free-standing porous membrane for sensing applications. Individual electrical contacts are made on the front side of the wafer while the infiltration of the probe and target molecules is done from the back avoiding any direct interaction of the molecules with the contact sites. We will report on the design considerations of the electrical porous silicon array and the preliminary results obtained using synthetic DNA as a model molecule.
INTRODUCTION The advances in the field of biotechnology and genetics have revealed information contained in the human genome associated with normal physiological processes as well as disease states. The mechanism of adaptation of organisms [1], and the genes responsible for the virulence of various pathogens have also been identified. DNA microarrays have an important role in this field since they allow the measurements of gene expression levels associated with different biological processes as well as toxicological effects of chemicals [2]. Identification of closely related bacteria such as Shigella, E. Coli and different Salmonella enterica serotypes can now be identified by microarrays using a specific gene that allows detection and discrimination between these species [3]. DNA microarrays are composed of an ordered arrangement of known sequences immobilized on the substrate so each "address" or "spot" is associated with a gene. When the microarray is exposed to a complex mixture of labeled DNA molecules, those participating in hybridization produce a signal; DNA sequences that are more abundant produce a stronger signal. The use of a microarray configuration allows the
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simultaneous analysis of several thousand genes,
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