Methylene blue-enhanced electrochemical oxidation of tyrosine residues in native/denatured bovine serum albumin and HIV-1 Tat peptide.

[Display omitted] • A selectively increasing Tyr oxidation signal system is constructed. • MB-based electro-generated reactive cation radicals can react with Tyr residues. • Amplified oxidation mechanisms of Tyr residues are demonstrated. • Denatured BSA can be distinguished from native BSA. • The proposed signal amplification method has ability to resist interference from Trp. The low-level electrochemical oxidation signals of amino acid residues always limit their applications in label-free protein biosensors. Herein, methylene blue (MB) is used to increase the oxidation signal of tyrosine (Tyr) residues in native/denatured bovine serum albumin (BSA) and HIV-1 Tat peptide. It is found that MB can remarkably amplify Tyr-based oxidation responses in BSA and peptide by MB-based electro-generated reactive radicals. The signal amplification mechanism is demonstrated by assessing the influences of various factors such as MB concentration, BSA concentration, solution pH, incubation temperature, amino acid sequence and chemical denaturation agents. The proposed signal enhancement method has significant advantages of good selectivity, high reproducibility and strong anti-interference ability. The present results provide new insight into Tyr-based oxidation signal amplification in label-free electrochemical protein biosensors by in-situ electro-generated reactive cation radicals. [ABSTRACT FROM AUTHOR]