Optimization of Mesoporous Silicon Microcavities for Proteomic Sensing
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Optimization of Mesoporous Silicon Microcavities for Proteomic Sensing L.A. DeLouise and B.L. Miller* Department of Dermatology and Center for Future Health, University of Rochester Medical Center, 697 Elmwood Ave, Rochester NY 14642 USA * University of Rochester, Departments of Biochemistry and BioPhysics, University of Rochester Medical Center, 697 Elmwood Ave, Rochester NY 14642 USA
ABSTRACT To expand the utility of p+ mesoporous silicon devices in proteomic biosensor applications, we have conducted in-depth studies to quantify the impact of employing a strong base post etch process to modify the microstructure of microcavity sensors tuned to operate in the visible spectrum. Changes in the optical response and quality of the cavity are quantified as a function of potassium hydroxide (KOH) exposure and initial porosity. Our results show that an aqueous ethanol solution containing millimolar concentrations of KOH is an effective means not only to increase the porosity and pore size, thereby enhancing pore infiltration of large (4050kDa) proteins, but also to fine tune the optical properties of a passive optical devices. INTRODUCTION Our laboratory is actively pursing the development of meso and macro porous silicon biosensors for the detection of pathogenic organisms. Mesoporous sensors leverage the photoluminescent and highly reflective optical properties of multilayer microcavity structures to transduce the sensor response. These structures have previously been used in label free detection of pathogenic substances using small molecule [1] and oligonucleotide [2] probes. Our efforts to extend the use of mesoporous silicon microcavity sensors to employ proteomic probes have proven challenging, presenting many unique requirements. Some of these are well recognized in the field of proteomics array technology and some are unique to the porous silicon device platform. For example, it is necessary to develop an understanding of the relationship between pore size and infiltration to protein molecular weight and shape [3]. There is an additional need to keep the protein probe functional in an immobilized state [4]. Finally, there are issues concerning nonselective binding within pores caused by entrapment and pH dependent electrostatic forces [5]. These concerns are believed linked to the root cause of an observed high level (~ 50%) of sensor false negatives in our preliminary efforts to develop a proteomic sensor prototype to detect the enteropathogenic and enterohemorrhagic strains of E. coli [6]. Utilizing mesoporous microcavities, we have observed surface wetting and pore infiltration issues with Intimin (38kDa) [7,8] and other large biomacromolecules such as Glutathione-STransferase (~50kDa). To improve pore infiltration of biomolecular probe/target systems we have endeavored to systematically alter the microstructure of mesoporous microcavities using dilute ethanolic KOH in a post-electrochemical etch processing step. The use of KOH to modify porous silicon has previously been reported [9, 10]; however, lit
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