This work examines the influence of charge density and surface passivation on the DNA-induced corrosion of porous silicon (PSi) waveguides in order to improve PSi biosensor sensitivity, reliability, and reproducibility when exposed to negatively charged DNA molecules. Increasing the concentration of either DNA probes or targets enhances the corrosion process and masks binding events. While passivation of the PSi surface by oxidation and silanization is shown to diminish the corrosion rate and lead to a saturation in the changes by corrosion after about 2 h, complete mitigation can be achieved by replacing the DNA probe molecules with charge-neutral PNA probe molecules. A model to explain the DNA-induced corrosion behavior, consistent with experimental characterization of the PSi through Fourier transform infrared spectroscopy and prism coupling optical measurements, is also introduced.

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In‐situ oligonucleotide synthesis through an 8‐base sequence is demonstrated within 30 nm silicon mesopores utilizing sequential phosphoramidite reactions. Stepwise attachment of each base is confirmed by monitoring the porous silicon effective refractive index via a waveguide resonance angle. A linear increase in the effective refractive index is observed after the addition of each base, and the detection of oligonucleotides containing only a single thymine is possible. It is estimated that 50% of the available internal pore surface is occupied by the 8‐base oligonucleotides, which is a substantially greater coverage than obtained by using traditional methods of direct attachment of presynthesized DNA oligonucleotides. The greater surface coverage by DNA probes will enable more effective biosensing devices. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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