Synthesis and characterization of conducting polymers containing polypeptide and ferrocene side chains as ethanol biosensors

A novel approach for the fabrication of a biosensor from a conducting polymer bearing polypeptide segments and ferrocene moieties is reported. The approach involves the electrochemical copolymerization of the electroactive polypeptide macromonomer and independently prepared ferrocene imidazole derivative of dithiophene, on the electrode surface. The polypeptide macromonomer was synthesized by the simultaneous formation of N-carboxyanhydride (NCA) and ring opening polymerization of N-Boc-L-lysine (α-amino acid of the corresponding NCA) using an amino functional bis-EDOT derivative (BEDOA-6) as an initiator. Alcohol oxidase was then covalently immobilized onto the copolymer coated electrode using glutaraldehyde as the crosslinking agent. The intermediates and final conducting copolymer before and after enzyme immobilization were fully characterized by FT-IR, 1H-NMR, GPC, cyclic voltammetry, SEM and EIS analyses. The newly designed biosensor which combined the advantages of each component was tested as an ethanol sensing system offering fast response time (9 s), wide linear range (0.17 mM and 4.25 mM) and low detection limit (0.28 mM) with a high sensitivity (12.52 μA mM−1 cm−2). Kinetic parameters KappM and Imax were 2.67 mM and 2.98 μA, respectively. The capability of the biosensor in determining ethanol content in alcoholic beverages was also demonstrated.