Exploring contaminants and analyte adsorption on functionalized porous silicon: Insights from a combined theoretical and experimental approach

Porous Silicon (PSi) holds significant promise in the realm of biosensor fabrication, due to its biocompatibility, large surface area, ease of fabrication and surface modification. The majority of the studies in the literature are experimental, primarily emphasizing phenomenological aspect and lack a theoretical understanding of the processes involved. This study adopts a systematic theoretical approach that employs density functional theory (DFT) to examine PSi models functionalized with –O and –OH groups. Using 3-aminopropyltrimethoxysilane (APTMS) and (3-aminopropyl)triethoxysilane (APTES) as probes for interaction with PSi, the interplay between this system and analytes is explored considering some typical organic molecules such as caffeine (CF), paracetamol (PC), methylene blue (MB), and astaxanthin (ASX). The interactions between PSi and the silanes are of a covalent nature, whereas the attraction among the silanes and contaminants leans towards electrostatic forces, aided by van der Waals interactions. Theoretical absorption spectra indicated that the shifts in intensity help to identify analytes/contaminants, as they are related to the degree of pore functionalization. This modeling gained further clarity through experimental monitoring performed through reflective interference fast Fourier transform spectroscopy and validation using X-ray photoelectron spectroscopy measurements on porous silicon films. In addition to the fundamental understanding of the functionalization processes, this combined theoretical-experimental approach establishes groundwork for futuristic studies in the field of porous silicon based chemical/bio-sensors and tailoring/designing novel materials for enhanced selectivity towards the desired analytes.