Porous Silicon Nanostructured Materials for Sensing Applications: Molecular Assembling and Electrochemical or Optical Ev
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Porous Silicon Nanostructured Materials for Sensing Applications: Molecular Assembling and Electrochemical or Optical Evaluation Márquez, J.1, De la Cruz-Guzmán, M.1, Cházaro, L.F.2, Palestino, G.1,* 1 Facultad de Ciencias Químicas, Universidad Autónoma de San Luis Potosí, Av. Manuel Nava No. 6, Zona Universitaria, CP 78210, San Luis Potosí, México. 2División de Ciencias Ambientales, Instituto Potosino de Investigación Científica y Tecnológica A.C., Camino a la Presa San José 2055, Col. Lomas 4ª sección C.P. 78216. San Luis Potosí, México. *Corresponding author: [email protected] ABSTRACT Porous silicon (PSi) combines the potential of miniaturization with a very large surface area. The PSi surface can be chemically modified resulting in a high sensitivity (low detection threshold) device for chemical and biomolecular sensing. In previous work, we have shown that redox proteins and fluorescent ligands can be infiltrated into PSi (PSiMc) structures. The hybrid devices have shown interesting new properties produced by the coupling of the individual properties of PSi nanostructures and the modifiers. In this work, we have obtained a PSiMc/redox protein bioelectrode, which presents a quasi-reversible electrochemical response. This effect was attributed to the semiconducting nature of the PSi substrate and to the functional groups of the crosslinking molecules (MPTS), which together produce a capacitive effect on the device. On the other hand, the chemical modification of PSiMc with fluorescent ligands allowed us to fabricate fluorescent PSi hybrid nanostructures, which were tested for the detection of environmental pollutants such as heavy metals (specifically Hg2+). We found that the selectivity of this optical device depends on the selected recognizing molecule. The captured metal induces the formation of a metallic complex that shows higher fluorescence compared with the sensor device. These results demonstrate the viability of using porous silicon as optical sensors and electrochemical biosensors. The infiltration of fluorescent recognizing molecules and proteins into the PSi matrix were evaluated by specular reflectance, FTIR spectroscopy, fluorescence spectroscopy and cyclic voltammetry. INTRODUCTION Nanostructures of porous silicon (PSi) have emerged as promising materials due to their unique and unusual optical and electrical properties compared to that of bulk Si (c-Si). The PSi substrate allows the possibility to develop optical and electrochemical devices through the covalent immobilization of either organic or inorganic compounds, which affords a more stable sensor device [1-3]. One advantage of this material is its large surface area, which allows the immobilization of large quantities of nanoparticles, organic molecules, and (bio) macromolecules with capacity to perform electron transfer reactions on its surface [4-6]. In addition, the optical properties of PSi can be easily tuned depending on the type of the structure produced by electrochemical etching, such as monolayer, bilayer, Bragg refle
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