Figure 2. The mechanism of TMB²⁺ etching AuNPs.

(A) The absorption spectrum of AuNPs (100 μL, tween-20 protected) in the presence of different additives. (a) 50 μL 0.1 M Br⁻ and 50 uL 0.2155 mM TMB²⁺; (b) 50 μL 0.1 M CTAC and 50 uL 0.2155 mM TMB²⁺; (c) 50 μL 0.1 M CTAB and 50 uL 0.2155 mM TMB²⁺; (d) 25 μL 0.2 M Br⁻ and 25 μL 0.2 M CTAC and 50 uL 0.2155 mM TMB²⁺; (e) 50 uL H₂O and 50 uL 0.2155 mM TMB²⁺; (f) 50 uL 0.1 M CTAB and 50 uL 1.5 mM H₂O₂; (g) 100 uL H₂O, insert was the corresponding colorimetric picture. (B) The absorption decrease value of AuNPs added with TMB²⁺ and H₂O₂ at different reaction time. (C) The UV-vis spectrum of TMB liquid substrate system used in this work, 0.2104 mM TMB²⁺ produced by the TMB system and 100 uL AuNPs with 100 uL 0.2104 mM TMB²⁺, all these three mixtures were diluted 10 times.