Balancing Redox Activity Allowing Spectrophotometric Detection of Au(I) Using Tetramethylbenzidine Dihydrochloride

Abstract

Aqueous, acid solutions containing balanced amounts of a strong reductant (formaldehyde, HCHO) and a strong oxididant (N-bromosuccinimide, NBS) allow the first sensitive spectrophotometric analysis of monovalent gold ion, Au(I), using oxidation of color reagent 3,3',5,5'-tetramethylbenzidine dihydrochloride (TMB). This new method enables various oxidation states of Au ion to be quantified by balancing reduction potential in a Au solution. At low reductant levels, NBS oxidizes Au(I), which linearly suppresses subsequent oxidation of TMB by NBS to its blue charge-transfer complex of diamine and diimine to 2.00 mg L(-1) of Au, resulting in reduced color formation. The linear range of Au(I) quantitation was increased substantially relative to existing methods: from 0.005 to 1.00 mg L(-1) (R(2) = 0.988). For this range, the limit of detection was 0.0025 mg L(-1), which is comparable to the best reported spectroscopic method to analyze Au(III). At relatively high reductant levels, Au(I) is reduced to Au(0), then subsequently oxidized from Au(0) to Au(III) by addition of NBS. TMB is oxidized to its blue charge-transfer complex via the reduction of the reoxidized Au(III) to Au(0). Balancing redox conditions of HCHO/NBS at a molar ration of 22.7 allows quantitative measurement of Au(I) across a linear concentration range of 0.05-2.00 mg L(-1) (R(2) = 0.997). This balancing redox condition could allow sensitive, quantitative, spectrophotometric analysis of other metal ions besides Au by targeting the metal ion's reduction potential with an associated redox-sensitive color reagent.

Versatile and Amplified Biosensing through Enzymatic Cascade Reaction by Coupling Alkaline Phosphatase in Situ Generation of Photoresponsive Nanozyme

“…This indicates that the originally inert TiO 2 NPs is photoactive under visible light irradiation (λ ≥ 400 nm) after their surface coordination by CA. The catalytic oxidation of TMB to its oxidation product (oxTMB) accounts for the above blue color development, which gives characteristic absorbance at 369 and 652 nm (Figure 2A) originating from its distinctive charge-transfer complex 29 of diamine and diamine (insert of Figure 2A). This catalytic oxidation reaction for TMB by the illuminated TiO 2 − CA is similar to that of natural enzymes, indicating its enzymelike activity.…”

Electron optics of nanoplasmonic metamaterials in bio/opto theranostics

“…37 Control of chemical and photo oxidation during tin 38 and silver 39 steps improves metal layer density and uniformity. Balancing oxidation in solution supports spectrophotometric analysis of Au(I) 40 and Sn(II) 41 at lower limit of detection than alternative methods. Random, two-dimensional (2D) assemblies of AuNP on silica have been thermally transformed from Au island film stably deposited by electroless plating.…”

Reductive spectrophotometry of divalent tin sensitization on soda lime glass

“…Two distinct one-electron products of TMB can be envisaged: TMB radical cation, and the charge-transfer complex of the diamine (electron donor) and the diimine (electron acceptor). Subsequent addition of surface-associated, reductant tin (II) (+0.15 V, NHE) to this volume at Stage 3 reversed the oxidation to a degree, resulting in equilibrium between the diimine and its blue, charge-transfer complex of diamine and diimine ( max = 370, 652 nm), as illustrated in Stage 4 [29,30,32]. The amount of tin (II) added determined the degree of this reversal, as indicated by spectroscopic peaks at 370, 452, and 652 nm shown in Fig.…”

“…TFA concentrations of 30, 68, and 90 mM were tested at sensitization concentration and time of 26 mM and 30 s, respectively. TFA was used instead of HCl during sensitization, due to reports indicating tin (II)-TFA sensitization was effective for subsequent EL plating of uniform gold films with features closely resembling sputtered gold films [7,13,29,30,34,39]. However, tin sensitization in the presence of TFA may reduce tin (II) on substrates, and produce larger grain size and higher pK a (0.23) than HCl (−7.0) [13].…”

“…Jang and Roper first used aqueous acid solutions in which formaldehyde, HCHO, and NBS were balanced with TMB-HCL to quantitate dissolved Au (I) [30]. Subsequently, Wei et al combined equal volumes of equimolar solutions of TMB-HCL and NBS to measure dissolved tin (II) from 0.05 g/mL (lower limit of quantitation, LOQ) to 0.34 g/mL (upper limit of quantitation, UOQ) [29].…”