Covalent functionalization and biomolecular recognition properties of DNA-modified silicon nanowires

The direct covalent modification of silicon nanowires with DNA oligonucleotides, and the subsequent hybridization properties of the resulting nanowire-DNA adducts, are described. X-ray photoelectron spectroscopy and fluorescence imaging techniques have been used to characterize the covalent photochemical functionalization of hydrogen-terminated silicon nanowires grown on SiO2 substrates and the subsequent chemistry to form covalent adducts with DNA. XPS measurements show that photochemical reaction of H-terminated Si nanowires with alkenes occurs selectively on the nanowires with no significant reaction with the underlying SiO2 substrate, and that the resulting molecular layers have a packing density identical to that of planar samples. Functionalization with a protected amine followed by deprotection and use of a bifunctional linker yields covalently linked nanowire-DNA adducts. The biomolecular recognition properties of the nanowires were tested via hybridization with fluorescently tagged complementary and non-complementary DNA oligonucleotides, showing good selectivity and reversibility, with no significant non-specific binding to the incorrect sequences or to the underlying SiO2 substrate. Our results demonstrate that the selective nature of the photochemical functionalization chemistry permits silicon nanowires to be grown, functionalized, and characterized before being released from the underlying SiO2 substrate. Compared with solution-phase modification, the ability to perform all chemistry and characterization while still attached to the underlying support makes this a convenient route toward fabrication of well characterized, biologically modified silicon nanowires.