Enzyme-less and selective electrochemical sensing of catechol and dopamine using ferrocene bound Nafionmembrane modified electrode

Abstract

Here in, we are reporting a new membrane modified electrode based on ferrocene (fc) mixed Nafion (Nf) system for enzyme-less and selective electrochemical sensing of catechol and dopamine without any interference from cysteine, uric acid, hydrogen peroxide and ascorbic acid at an applied potential of 200 mV vs. Ag/AgCl in pH 7 phosphate buffer solution. The working electrode, ferrocene-bound Nafion membrane modified glassy carbon electrode (GCE/{Nf-fc}-MME) was prepared by manual mixing of 10 mg of ferrocene with 2% of Nafion solution (optimal) followed by drop coating on the GCE surface, and electrochemical pretreatment by continuous potential cycling in pH 7 PBS. The modified electrode showed well-defined redox behavior at an equilibrium potential (E_1/2) of 150 mV vs. Ag/AgCl in pH 7 PBS due to the electron-transfer reaction of fc/fc⁺ redox. The calculated exchange current density (I^o) and apparent heterogeneous rate constant (k_h^app) were 6.16 × 10⁻⁵ A and 4.51 × 10⁻³ cm s⁻¹ respectively for catechol by electrochemical impedance spectroscopy, which were about 100 times higher over the unmodified electrodes. Different domains of Nafion, namely hydrophilic and hydrophobic sites have a specific role to immobilize the ferrocene species and in turn to selectively mediate catechol and dopamine in a solution mixture containing common physiological interferents. Calibration plots were in the range of 250 μM–2.5 mM and 250 μM–5 mM for catechol and dopamine, respectively, with the corresponding detection limit (S/N = 3) values 10.8 μM and 22.7 μM. The current sensitivity was 1.1 μA mM⁻¹ for both the compounds. The working electrode showed negligible variation in the detection current up to 2 days of measurement.