Innovative polymer engineering for the investigation of electrochemical properties and biosensing ability

Subtle engineering for the generation of a biosensor from a conjugated polymer with the inclusion of fluorine-substituted benzothiadiazole and indole moieties is reported. The engineering includes the electrochemical copolymerization of the indole-6-carboxylic acid (M1) and 5-fluoro-4,7-bis(4-hexylthiophen-2-yl)benzo[c][1,2,5]thiadiazole (M2) on the indium tin oxide and graphite electrode surfaces for the investigation of both their electrochemical properties and biosensing abilities with their copolymer counterparts. The intermediates and final conjugated polymers, Poly(M1) [P-In6C], Poly(M2) [P-FBTz], and copoly(M1 and M2) [P-In6CFBTz], were entirely characterized by ¹H NMR, ¹³C NMR, CV, UV-Vis-NIR spectrophotometry, and SEM techniques. HOMO energy levels of electrochemically obtained polymers were calculated from the oxidation onsets in anodic scans as -4.78 eV, -5.23 eV, and -4.89 eV, and optical bandgap (Eg^op) values were calculated from the onset of the lowest-energy π-π* transitions as 2.26 eV, 1.43 eV, and 1.59 eV for P-In6C, P-FBTz, and P-In6CFBTz, respectively. By incorporation of fluorine-substituted benzothiadiazole (M2) into the polymer backbone by electrochemical copolymerization, the poor electrochemical properties of P-In6C were remarkably improved. The polymer P-In6CFBTz demonstrated striking electrochemical properties such as a lower optical band gap, red-shifted absorption, multielectrochromic behavior, a lower switching time, and higher optical contrast. Overall, the newly developed copolymer, which combined the features of each monomer, showed superior electrochemical properties and was tested as a glucose-sensing framework, offering a low detection limit (0.011 mM) and a wide linear range (0.05-0.75 mM) with high sensitivity (44.056 μA mM^-1 cm^-2).