Metal-enhanced biosensor for genetic mismatch detection

DNA biosensors are increasingly used in hybridization reactions, mutation detection, genomic sequencing, and identification of pathogens. However, the inability to monitor the recognition signals without resorting to the use of labels or electroactive mediators has led to DNA devices with inadequate sensitivity. Moreover, some electroactive species require high redox potentials that often destroy the DNA complementarity. This article presents the concept of metal-enhanced detection (MED) for the determination of DNA-DNA reactions and presents the application of this concept for mismatch detection. The MED concept relies on the idea that metallic films deposited as a continuous layer or monolayer onto a solid electrode, or even electrostatically held, could greatly enhance the rate of electron transfer by reducing the distance between the donor and acceptor species and could lead to label-free assays during DNA hybridization reactions. The MED concept has been tested for voltammetric detection of gene sequence of Microcystis spp. The resulting biosensor involved the immobilization of a 17-mer DNA probe that is complementary to a specific gene sequence of Microcystis spp. on a gold electrode via avidin-biotin chemistry. Electrochemical reduction and oxidation of DNA-captured Ag(+) ions provided the detection signals for the target gene sequence in solution. A linear response of silver cathodic peak current with concentration of the target oligonucleotide sequence was observed with a detection limit of 7 x 10(-9)M. This label-free approach was successfully applied to detecting two-base-pair mismatches in the gene sequence of Microcystis spp.