DNA biosensor using fluorescence microscopy and impedance spectroscopy

Two types of DNA biosensors are presented. Both sensing principles are demonstrated using synthetic oligomer single-stranded DNA (ssDNA) with concentrations in the micromolar range. A first sensor type is based on the detection of fluorescently labeled ssDNA to a complementary probe that is bound to a silicon substrate by a disuccinimidyl terephtalate and aminosilane immobilization procedure. An enhanced fluorescent response is obtained using constructive interference effects in a fused silica layer deposited before immobilization onto the silicon substrate. The selectivity of different DNA probes towards complementary and non-complementary DNA targets is tested. A second type of DNA sensor is based on the impedimetric response of a solution of unlabeled 20-mer ssDNA in de-ionized water. Interdigitated microelectrodes that are 5 mu m wide and separated by 5 mu m gaps are microfabricated on glass substrates and the complex impedance of the system in the 100 Hz-100 MHz frequency range is investigated. The proportionality between the measured solution resistance and ssDNA concentration is demonstrated. (c) 2006 Elsevier B.V. All rights reserved.