Dual Detection Platform with Refractive Index and SERS Sensing Based on Colloidal Gold Functionalized Porous Silicon Sub
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Dual Detection Platform with Refractive Index and SERS Sensing Based on Colloidal Gold Functionalized Porous Silicon Substrates Yang Jiao,1 Dmitry S. Koktysh,2,3 Sharon M. Weiss1,3,a) 1
Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, TN 37235, U.S.A. 2 Department of Chemistry, Vanderbilt University, Nashville, TN 37235, U.S.A. 3 Vanderbilt Institute of Nanoscale Science and Engineering, Vanderbilt University, Nashville, TN 37235, U.S.A. ABSTRACT We demonstrate a dual-mode sensing platform based on porous silicon (PSi) substrates coated with colloidal gold (Au) nanoparticles (NPs). This Au-PSi composite structure supports both molecular fingerprinting via surface enhanced Raman scattering (SERS) and quantification of molecular binding via reflectance measurements. Reflectance shifts of 7-10 nm in the infrared region were observed in the case of adsorbing benzenethiol or antioxidant glutathione molecules on the surface of Au NPs. Subsequent SERS measurements showed unique identification for both molecules and provided a < 1 μM and < 1 mM detection resolution for benzenethiol and glutathione, respectively. INTRODUCTION Porous materials have been widely utilized as host materials in label free sensing applications due to their significantly enhanced surface area for molecular binding. The attached molecules on the pore walls lead to the overall refractive index change of the porous layer because porous silicon can be treated as an effective medium. In optical biosensors even a small refractive index change can result in measureable changes of an optical signal (e.g., reflection, transmission, or photoluminescence), which are monitored to detect and quantify the molecular bindings. Porous material-based single layer films [1], waveguides [2] and microcavities [3] have been reported for detection of molecular binding events with high detection sensitivity [4]. However, the above sensing templates rely on biochemical functionalization to provide specificity and lack the ability to perform unique molecular identification based solely on the method of optical signal interrogation. Surface enhanced Raman scattering (SERS) measurements, on the other hand, can supply unique molecular information through wavelength shifts due to molecular vibrations. The enhanced electromagnetic field at metal surfaces significantly increases the intensity of peaks in the Raman spectrum. Recently, porous materials have attracted much attention as promising SERS substrates since nanoscale porous structures can serve as templates for metal deposition to form nanoscale porous metal structures [5, 6]. The decoration of metal inside the pores can supply more nanoscale metallic surface within the laser excitation region compared to planar SERS substrates, thus giving rise to an efficient three-dimensional (3D) SERS effect.
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In this work, we report a dual-mode sensing platform based on PSi impregnated with ~4.5 nm colloidal gold (Au) nanoparticles (NPs
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