A feasibility study of a capacitive biosensor for direct detection of DNA hybridization

This preliminary study was performed to prove the feasibility of a direct c apacitive DNA biosensor for detection of nucleic acids. Two different metho ds for immobilization of the oligonucleotide probes were used. The first ty pe of sensor was composed of a gold rod with a self-assembled monolayer of a 26-base long oligonucleotide probe, modified with an SH-group at the 5'-e nd. Coverage studies showed that only around 20% of the surface uas covered , probably due to the bulky nature of the probes. Hybridization studies per formed in a flow-through cell showed selectivity towards a DNA sample conta ining single stranded fragments of cytomegalo virus (CMV) possessing a comp lementary sequence. As few as 25 molecules could be detected at sample conc entrations of 0.2 attomolar with an injection volume of 250 mu L. Controls with fragments of double-stranded CMV and single-stranded hepatitis B virus and tyrosinase mRNA gave all lower responses. The other type of sensor was modified by covalent immobilization of a phosphorylated 8-base long oligon ucleotide probe to a self-assembled monolayer of cysteamine. This biosensor also showed selectivity against single stranded fragments of CMV and also in this case as few as 25 molecules could be detected.