Surface Plasmon Resonance Spectroscopy and Electrochemistry Study of 4-Nitro-1,2-phenylenediamine:  A Switchable Redox Polymer with Nitro Functional Groups

Electrochemistry and electrochemical surface plasmon resonance (SPR) spectroscopy have been applied to study the electrochemical deposition and the redox transition of poly(4-nitro-1,2-phenylenediamine) (P4NoPD) on gold disk. It was shown that SPR can be the signal transducer for the different redox states of P4NoPD. Using a model biomolecular system, involving streptavidin, biotinylated DNA, and its complementary target DNA, it was found that the presence of nitro groups in P4NoPD allows the biorecognition events to be modulated by voltages. There is minimal nonspecific binding of biomolecules on oxidized (+0.2 V) or as-prepared P4NoPD, and binding occurs more significantly on the reduced P4NoPD (−0.2 to −0.6 V) with the presence of amine groups. The electrochemical deposition of P4NoPD film was also conducted on boron-doped diamond (BDD) electrode. The stability of the reduced P4NoPD film on gold and BDD was comparatively evaluated by electrochemical impedance spectroscopy (EIS). The result showed that BDD allows the electrochemical reduction of the P4NoPD film at wider cathodic limits than gold.