Macroporous silicon electrical sensor for DNA hybridization detection

Macroporous silicon (pore diameter 1-2 microm) was used in an electrical sensor for real time, label free detection of DNA hybridization. Electrical contacts were made exclusively on the back side of the substrate, which allowed complete exposure of the porous layer to DNA. Hybridization of a DNA probe with its complementary sequence produced a reduction in the impedance and a shift in the phase angle resulting from a change in dielectric constant inside the porous matrix and a modification of the depletion layer width in the crystalline silicon structure. The effect of the DNA charge on the response was corroborated using peptide nucleic acid (PNA), an uncharged analog of DNA. The sensitivity and selectivity of the device were characterized and the sensing properties of the porous layer alone were investigated using self-supporting macroporous silicon membranes.