Porous silicon (PSi) can be used as smart transducer material in sensing application, and in particular in the detection of vapors, liquids and biochemical molecules. In fact, on exposure at chemical substances, several physical quantities, such as refractive index, photoluminescence, and electrical conductivity, change drastically. A key feature of a physical transducer, being sensitive to organic and biological molecules, either in vapor and liquid state, is a large surface area: PSi has a porous sponge-like structure with a specific area of the order of 200 - 500 m2cm-3, so that it can assure a very effective interaction with several adsorbates. Moreover, PSi is an available, low cost material, compatible with standard IC processes, so that it could usefully be employed in the realization of smart sensors and microsystems. In particular, in the last years, a lot of experimental work has been reported concerning its use as optical sensors in chemical and biological sensing. PSi monolayers were used as trial substrates in order to attach synthetic oligonucleotides for biosensing purposes. The critical issue in DNA recognition is the chemistry of the probe-oligonucleotides immobilization on the PSi surface, from which seems to depend on the stable and affordable sensor operation. Many of the results carried out to day, derived from the standard DNA immobilization chemistry exploited on silicon-oxide rich substrates (such as glass), involve the silanization of the oxidized PSi surface. A promising recently proposed alternative is that exploiting the reaction of acids molecules with the hydrogen-terminated porous silicon surface in order to obtain a more stable organic layer covalently attached to the PSi surface through Si-C bonds. In this work, we present new results about sensing of bio-chemical substances based on the functionalization of the hydrogen-terminated porous silicon surface by means of Si-C bonds.

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