Fig. 2

Colorimetric BCA assay of Cu(I)(aq) concentrations. a Spectra of BCA added to 50 µM Cu(II) azurin (black dashes) and added to a reacted mixture of 50 µM Cu(II) azurin with 10 (black), 20 (red), 30 (blue), and 40 nm Ag ENMs (grey). The BCA-Cu(I) complex (λmax = 562 nm) presents as a shoulder on the Cu(II)-thiol LMCT band from Cu(II) azurin (λmax = 630 nm). b Deconvolution of UV–Vis spectra enables comparison of Cu(I)(aq) and Cu(II) azurin concentrations after reaction with Ag ENM of various sizes. Control spectra for BCA assays and sample deconvoluted spectra are given in Additional file 1: Figure S2