Electrochemical properties and electrocatalytic activity of FAD immobilized onto cobalt oxide nanoparticles: Application to nitrite detection

Cyclic voltammetry has been used for modification of glassy carbon (GC) electrode with cobalt oxide (CoOx) nanoparticles and flavin adenine dinucleotide (FAD) film. Electrodeposited cobalt oxide may be a promising material for FAD immobilization owing to its high biocompatibility and large surface. The adsorbed FAD film is stable and electrochemically active in aqueous solution. The FAD films assembled on cobalt oxide exhibited a pair of well defined, stable and nearly reversible CV peaks at wide pH range. The formal potential of adsorbed FAD onto cobalt oxide nanoparticles film, E0′ vs. Ag/AgCl reference electrode is −0.44 V in pH 7 buffer solution was similar to dissolved FAD and changed linearly with a slope of 46 mV/pH in the pH range 4–12. The surface coverage and heterogeneous electron transfer rate constant (ks) of FAD immobilized on CoOx film glassy carbon electrode are 1.47 × 10−9 mol cm−2 and 0.85 ± 0.1 s−1, indicating the high loading ability of the CoOx nanoparticles and great facilitation of the electron transfer between FAD and CoOx nanoparticles. Cobalt oxide/FAD composite modified GC electrode shows excellent catalytic activity for nitrite reduction at reduced overpotential. Furthermore, FAD/CoOx rotating disk electrode modified GC electrode shows good analytical performance for amperometric determination nitrite. Under optimized condition of the amperometry method the concentration calibration range, detection limit and sensitivity are 1–30 μΜ, 0.20 μM and 10.5 nA/μM, respectively. Finally the kinetics of the catalytic reaction between nitrite anion and reduced FAD was characterized, using cyclic voltammetry and a value of 2.08 (±0.3) × 103 M−1 s−1 was obtained for the rate constant.