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[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]

Nano-sized TiO 2 and tris(hydroxymethyl)aminomethane (Tris) are widely used in diverse commercial products such as cosmetics, medicines and paints, therefore their possible exposure and consequent risk to humans and natural environments rouse public concerns. This paper evaluates potential health risks of UV-excited TiO 2 and Tris buffer by constructing a decoloration/recoloration cycling-associated photo-stimulated fuel cell and using methylene blue (MB) as a color indicator through photo-oxidative damage of bovine serum albumin (BSA). Nano-TiO 2 can bind BSA and MB to form TiO 2 @BSA-MB hybrids, revealed by TiO 2 -tuned binding constant, fluorescence quenching constant and MB-induced BSA configuration transition. The color retention efficiencies after decoloration/recoloration cycling and photocurrent responses from photo-stimulated fuel cells are able to monitor the photo-oxidative damage to BSA. Furthermore, Tris can be oxidized in photo-stimulated fuel cells in the absence of BSA whereas BSA has ability to depress the photocatalytic oxidation of Tris, which is found to increase the photo-oxidative damage of BSA caused by TiO 2 and MB, therefore the simultaneous presence of TiO 2 , MB and Tris synergistically increases the photo-oxidative damage of BSA. The present results show new approaches for assessing the increased hazards to human health caused by photoradiation, nanomaterials and organic additives. Unlabelled Image • A decoloration/recoloration cycling-associated photo-stimulated fuel cell is built. • Photo-physical measurements suggest formation of TiO 2 @MB-BSA hybrids. • Color retention efficiency/photocurrent are able to evaluate BSA photodamage. • TiO 2 , MB and Tris synergistically increase photo-oxidative damage of BSA. • This study shows new approaches to assess the increased hazards to human health. [ABSTRACT FROM AUTHOR]