Investigation of electrochemical polymerisation of L-lysine and application for immobilisation of functionalised graphene as platform for electrochemical sensing

Abstract

Electrochemically synthesised poly-L-lysine (PLL) was employed to attach functionalised graphene (fG) to the electrode surface. The electropolymerisation conditions such as pH, monomer concentration, potential scan rate and number of cycles were optimised. Despite reports in the literature about electrochemical synthesis of PLL at pH between 8 and 10, the best pH for the polymerisation on carbon substrates was found 5.0–6.0. The best number of cycles was 4–5 with the scan rate of 10 mV s−1. The obtained PLL was characterised using scanning electron and atomic force microscopies and reflection-absorption infra red spectroscopy. The latter method confirmed formation of polymeric species at the interface through the amide bond. Atomic force microscopy showed that thin film covers whole surface but also forms some spikes indicating that polymerisation starts at nucleation points on defects of the substrate. The PLL film was applied to attract fG to the electrode surface. The best electrochemical properties of the electrode were obtained using layer-by-layer deposited fG/PLL/fG/PLL/GCE (glassy carbon electrode). Such an electrode was sensitive to dopamine determination in the presence of ascorbic and uric acids.