Competitive approach to the electrochemical detection of phosphopeptides on a porous ZrO2 thin film electrode

A competitive adsorption strategy has been designed to electrochemically detect phosphopeptides (P-peptides) based on the specific binding between ZrO2 and P-peptides. In this method, a porous ZrO2 thin film electrodeposited on a glassy carbon electrode was used to competitively capture P-peptides from their mixture with non-phosphopeptides labelled with electrochemical probe of ferrocene (Fc-peptides). The Fc-peptides previously adsorbed on the ZrO2 film modified electrode to saturation can be replaced by the non-electroactive P-peptides by competing the binding sites on ZrO2, resulting in a decrease of peak current of Fc-peptide/ZrO2 modified electrode. The change of peak current is directly related to the concentration of the P-peptides in solution, and thus, P-peptides can be quantitatively determined. The results reveal that the decreased peak current is linear proportional to the logarithm of the concentration of P-peptides from 0.1 mu M to 500 mu M with a detection limit of 0.0934 mu M (S/N = 3), showing the high sensitivity of the competitive biosensor. Results show that the adsorption of Fc-peptides on the modified electrode follows the first-order kinetics. The binding rate constant k(b) and the dissociation rate constant k(d) are calculated as 49.6 M-1 s(-1) and 1.97 x 10(-3) s(-1), respectively. The present approach offers a useful platform for the detection of phosphopeptides and will be a promising strategy for the electrochemical study of protein post-translational modification. (C) 2016 Elsevier B.V. All rights reserved.