Development of a label-free electrochemical DNA biosensor for the model analyte of breast cancer related sequences

In this work, a label-free electrochemical DNA biosensor capable of detecting a single-mismatch in a breast cancer gene 1 (BRCA1) related sequence was developed. Single nucleotide polymorphisms in the BRCA1 tumour suppressing gene have been reported to cause breast cancer, a genetic-based disease that is one of the leading causes of mortality worldwide. The label-free biosensor platform consisted of graphene, a phenyl linker and gold nanoparticles, immobilised on a glassy carbon electrode. To this anchoring layer, a 19 mer, thiol-labelled DNA probe was covalently attached, followed by hybridisation with its complementary target, a BRCA1 related DNA sequence, and finally zirconium was incorporated into the DNA duplex for electrochemical signal amplification. In this work, a two-level factorial design was used for optimisation of the significant factors and their interactions in biosensor performance. The change in oxidation current of ferrocenecarboxylic acid following hybridisation was used to voltammetrically study the analytical performance of the biosensor. Using square wave voltammetry, a linear dynamic range between 15.5 and 100 nM of the DNA target, with a detection limit of 4.6 nM and reproducibility of 4% was achieved.