Oxidized 3,3',5,5'-tetramethylbenzidine nanobelts enhance colorimetric sensing of H₂O₂

Herein, oxidized 3,3',5,5'-tetramethylbenzidine (oxTMB) nanobelts were developed to enhance the colorimetric and paper-based sensing of H₂O₂. It was found that the minor component of Fe²⁺ in Na₂SO₄ reagent could catalyze the oxidization of TMB by H₂O₂ into positively charged oxTMB, which was further assembled into dark blue oxTMB nanobelts via electrostatic interaction with SO₄^2-. The extinction originating from the absorption and scattering of oxTMB nanobelts was utilized to quantitatively detect H₂O₂ with a wide linear detection range (1.0-300 μM) and a low limit of detection (0.48 μM). In addition, no coffee-ring effect was observed in the test zone of the paper-based colorimetric array, which was beneficial to judge the color by naked eye. Finally, the colorimetric method was applied to detect H₂O₂ in contact lens care solution. This work not only proposed a new colorimetric sensing platform for H₂O₂, but also highlighted the minor component in the reagent might influence the experimental result.