The application of electrodeposited poly(propylene imine) dendrimer as an immobilisation layer in a simple electrochemical DNA biosensor

We describe the application of poly(propylene imine) dendrimer in the preparation of a simple DNA biosensor. Generation one PPI was electrodeposited via cyclic voltammetry on glassy carbon electrode using a potential range of -100 to 1100 mV for 10 cycles at 50 mV/s scan rate. A single strand probe DNA (21 mer) of 2 μM concentration was immobilised by electrostatic attraction on the PPI layer via deep coating in a 500 μL solution for 3 hr at 25 °C to form the biosensor (GCE/G1PPI/ssDNA). Hybridisations were carried out at 38 °C using blank buffer solutions and target DNA solutions comprising of complementary, non complementary and 3 base mismatch DNA strands. Electrochemical impedance spectroscopy presented as Nyquist, impedance and phase angle plots, was used to interrogate each stage of the biosensor preparation with Fe(CN)₆]^3-/4- as the redox probe. The biosensor hybridisation performance was monitored using charge transfer resistance data obtained after fitting the impedance plot. The DNA biosensor was able to detect complementary DNA target to the limit of 9.43 × 10-^-12 M with a linear range of 1 × 10-^-11 M to 5 × 10^-9 M. The biosensor was also selective towards mismatch and non complementary target DNA.