Decoupling of the Confused Complex in Oxidation of 3,3′,5,5′-Tetramethylbenzidine for the Reliable Chromogenic Bioassay

Abstract

Regulation of the reaction pathways is a perennial theme in the field of chemistry. As a typical chromogenic substrate, 3,3′,5,5′-tetramethylbenzidine (TMB) generally undertakes one-electron oxidation, but the product (TMB ox1 ) is essentially a confused complex and is unstable, which significantly hampers the clinic chromogenic bioassays for more than 50 years. Herein, we report that sodium dodecyl sulfate (SDS)-based micelles could drive the direct two-electron oxidation of TMB to the final stable TMB ox2 . Rather than activation of H 2 O 2 oxidant in the one-electron TMB oxidation by common natural peroxidase, activation of the TMB substrate by SDS micelles decoupled the thermodynamically favorable complex between TMB ox2 with unreacted TMB, leading to an unusual direct two-electron oxidation pathway. Mechanism studies demonstrated that the complementary spatial and electrostatic isolation effects, caused by the confined hydrophobic cavities and negatively charged outer surfaces of SDS micelles, were crucial. Further cascading with glucose oxidase, as a proof-of-concept application, allowed glucose to be more reliably measured, even in a broader range of concentrations without any conventional strong acid termination.

Facile Estimation of Surface Oxygen Vacancies in Co3O4 Catalysts with a Colorimetric Method

“…27−29 Colorless TMB can be oxidized to form blue product (oxTMB) by some reactive oxygen species. 29,30 Recent studies revealed that surface Ov can serve as the absorption site of H 2 O 2 or dissolved O 2 , and then H 2 O 2 or dissolved O 2 reacts with the trapped electrons on the metal oxide surface to produce some active oxygen species. 31 For example, the surface Ov of ZnO could serve as the active site for transformation of H 2 O 2 into a hydroxyl radical ( • OH), 32 and the surface Ov of TiO 2 could convert the dissolved O 2 to a superoxide anion radical (O 2…”

“…A colorimetric method is frequently regarded as a popular measurement technique due to its simplicity, convenience, and low cost. , Without the aid of any other advanced facilities, the colorimetric method is suitable for field analysis and point-of-care test. − As one classic chromogenic regent, 3,3′,5,5′-tetramethylbenzidine (TMB) features specific interest because of its high response sensitivity and low toxicity. − Colorless TMB can be oxidized to form blue product (oxTMB) by some reactive oxygen species. , Recent studies revealed that surface Ov can serve as the absorption site of H 2 O 2 or dissolved O 2 , and then H 2 O 2 or dissolved O 2 reacts with the trapped electrons on the metal oxide surface to produce some active oxygen species . For example, the surface Ov of ZnO could serve as the active site for transformation of H 2 O 2 into a hydroxyl radical ( • OH), and the surface Ov of TiO 2 could convert the dissolved O 2 to a superoxide anion radical (O 2 •– ) .…”

“…H 2 O 2 cannot directly oxidize TMB, while the active oxygen species can oxidize colorless TMB to produce blue oxTMB. 29,30 On the basis of the above discussion, it is possible to use the TMB-H 2 O 2 colorimetric system for quantifying the surface Ov in metal oxides.…”