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Porous silicon (PSi)-based biosensors are a promising platform for quantitative rapid diagnostics, but they have not broadly realized clinically relevant limits of detection due, in part, to poor baseline stability. Baseline instability can be attributed to two major physicochemical challenges - hydrolysis of PSi in aqueous solutions and fouling by unwanted biological species, both of which can obscure the detection of target molecules at low concentrations. In this work, PSi was thermally hydrosilated with vinylbenzyl chloride (VBC) to incorporate hydrolytically stable Si−C bonding and to provide an attached alkyl halide termination for further chemistry. Subsequent grafting of zwitterionic poly(sulfobetaine methacrylate) (SBMA) from this PSi-VBC layer by surface-initiated atom-transfer radical polymerization (siATRP) formed an antifouling coating. Films both with and without the antifouling polymer were exposed to PBS (pH 7.4) and human blood serum, and optical reflectance measurements were used to monitor hydrolysis and nonspecific adsorption. PSi-VBC-polySBMA surfaces exhibited little to no nonspecific binding, as determined by ATR-FTIR and optical reflectance measurements, due to their hydrophilicity. The compatibility of hydrosilylation and siATRP with various chemical groups provides significant versatility in this surface chemistry approach, as well as facilitates the incorporation of highly specific capture agents. By directly addressing the issues of hydrolysis and fouling, this strategy holds promise for reducing the limits of detection in complex biological samples.