Immobilization of single stranded DNA probe onto polypyrrole-polyvinyl sulfonate for application to DNA hybridization biosensor

Electrochemical DNA biosensor based on polypyrrole-polyvinyl sulfonate (PPy-PVS) coated onto Pt disc electrode (∼0.03 cm2) has been fabricated by immobilizing 25 bases long single stranded probe polydeoxycytidine (dC) using both biotin–avidin binding (indirect immobilization) and carbodiimide coupling (direct immobilization), to detect 25 bases long complementary target sequence polydeoxyguanosine (dG). These DNA immobilized electrodes have been characterized using differential pulse voltammetry (DPV), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) techniques, respectively. Compared to the indirect method of immobilization, direct immobilization of dC probe results in enhanced detection limit by 2200 times (upto 0.01 fmol) and improved sensitivity by about six times. These DNA electrodes have response time of 30 s and are stable for about 4 months when stored at 4 °C.