A DNA diagnostic biosensor: development, characterisation and performance

The aim of this work is to develop a sensor for specific DNA sequences, usi ng non-complex synthetic single-stranded oligonucleotides as a model system . A capacitance-based sensor for the direct detection of DNA sequences is d escribed. Hybridisation of analyte DNA with immobilised DNA on the silicon surface induces charge effects, altering the dielectric properties of the b iolayer, and can be detected by the associated change in the measured capac itance. DNA has been immobilised on a silicon electrode either by passive a dsorption or covalent coupling via 4-aminobutyldimethylmethoxysilane (4-ABD MMS). The work presented here introduces a colourimetric immunodetection te chnique for the evaluation of the immobilisation process and describes the electrical characterisation and performance of three silicon-based sequence -specific DNA sensors. These sensors consisted of a standard electrolyte-in sulator-semiconductor (EIS) structure with covalently bound probe DNA, a me chanically degraded structure with passively adsorbed probe DNA and a mecha nically degraded structure with covalently bound probe DNA. The last device had an improved signal to noise ratio and was, therefore, used to construc t a standard curve, revealing a detection Limit of 100 pmol DNA. On additio n of analyte DNA, then was a decrease in measured capacitance. This respons e was fast, specific and required no addition of mediators to enhance or am plify the signal. This device can be optimised for the detection of complex sequences. (C) 2000 Elsevier Science S.A. All rights reserved.