| Abstract
| - We describe the first determination of thiol compounds with gold nanocomposites composed of gold nanoparticlesand thermoresponsive copolymers having polyamino groups. The gold nanocomposites, which are used as a chromaticsensor, reveal chromatic change from blue to red with thermal stimuli, heating followed by cooling the solution. Theblue-to-red chromatic change results from disassembly of the gold nanocomposites, which arises from shrinkage ofthe thermoresponsive copolymers bound to the gold nanoparticle surfaces due to the phase transition induced bythermal stimuli. The disassembly is inhibited by addition of thiol compounds through displacement of the adheredthermoresponsive copolymers. The detached copolymers no longer influence morphological change of the goldnanocomposites. Corresponding with increase of concentration of the thiol compounds, a solution of the goldnanocomposites after the thermal stimuli shows chromatic change, which was quantified with the a* value in L*a*b*chromatic coordinates. A linear relationship between the a* value and concentration of cysteine, examined as abio-important thiol, is obtained below 7 × 10-6 mol dm-3, estimating a detection limit defined as 3σ of the blankto be 2.8 × 10-7 mol dm-3. The chromatic sensor of the gold nanocomposites is applied to the determination of cysteinein commercial supplements containing ascorbic acid, which seriously interferes with redox-based determination ofcysteine. Analytical results obtained with the chromatic sensor are identical to those obtained with HPLC.
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