Figure 1.

(A) UV/vis absorption spectra and optical photographs of 4 nM Au NPs in the absence (curve/tube a) and presence of BDBA (curve/tube b) or H₂O₂-treated BDBA (curve/tube c). The final concentrations of BDBA and H₂O₂ used were 0.6 mM and 1 mM, respectively; (B) Schematic illustration of BDBA-induced aggregation of citrate-capped Au NPs and reaction between BDBA and H₂O₂; (C) TEM images of Au NP suspension in the presence of BDBA (top) and H₂O₂-treated BDBA (bottom).