Conclusions In the present study, we propose and validate by optical measurements a new method to achieve the in situ synthesis of tailored oligonucleotide sequences on porous silicon supports suitable for label-free optical biosensing. In particular, we demonstrate that,

differently from aqueous ammonia, the use of dry ammonia in methanol allows the effective deprotection of nucleobases without harming the structural integrity of the porous silicon matrix, thus opening the way for the direct growing of mixed-sequence ONs on optically active PSi supports using exclusively inexpensive standard phosphoramidites. A 19-mer FK228 in vivo mixed-sequence 5′-GATTGATGTGGTTGATTTT-3′ has been synthesized in mesoporous PSi microcavities, resulting in a medium-yield process, mainly due to the average pore size (about 20 nm). PSi photonic devices with pore dimensions greater than that value, but always compatible with high optical quality response in the visible-near-infrared, therefore between 50 and 100 nm, will be considered in the next experiments,

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