Amplified Electrochemical Response of Phenol by Oxygenation of Tyrosinase Coupling with Electrochemical-chemical-chemical Redox Cycle

In this work, an novel electrochemical-chemical-chemical (ECC) redox cycle was designed in an enzyme-based sensor for acquiring additional signal amplification. The tyrosinase (Tyr) was entrapped in a sulfonated polyaniline−chitosan (SPAN−CS) composite which was used as a redox capacitor on a glass carbon electrode. Firstly, the substrate, phenol was catalyzed to catechol and further catalyzed to o-benzoquinone by Tyr. Next, in the presence of Ru(NH 3 ) 6 Cl 2 , the reduced state of SPAN(SPAN red ) was reacted with o-benzoquinone to form it's oxidized state (SPAN ox ) and catechol, then SPAN ox was reduced back to SPAN red by Ru(II) in the solution. Finally, the amplified anodic current of catechol was obtained on electrode through above ECC redox cycle system. In addition, the ECC redox cycling led to a high signal-to-background ratio. The voltammetric response showed excellent analytical performance to phenol over two linear range of 3.5 to 200.0 nmol L −1 and 200.0 to 2000.0 nmol L −1 with a high sensitivity of 2204 μA mM −1 . The detection limit was obtained to be 0.8 nmol L −1 (S/N=3). Furthermore, the proposed approach exhibited good repeatability, stability and specificity, and could offer practicality in the detection of phenol in tap water.