Ractopamine as a novel reagent for the fabrication of gold nanoparticles: Colorimetric sensing of cysteine and Hg2+ ion with different spectral characteristics

We have developed a facile and cost-effective chemical reduction procedure for the preparation of gold nanoparticles (AuNPs) using ractopamine hydrochloride (RA) as a novel reagent. The RA assembled AuNPs display high affinity towards cysteine (Cys) and Hg2+ ion, causing aggregation of RA-AuNPs, which accompanies a remarkable a red-shift (534 to 606 nm) for Cys and a blue-shift (534 to 506 nm) for Hg2+ ion in the surface plasmon resonance (SPR) band of RA-AuNPs. The UV-visible absorption spectral data revealed that linear calibration curves were obtained between absorption ratios (A(606)/A(534) for Cys and A(506) for Hg2+ ion) and the concentration range from 0.6 to 600 mu M and from 1 to 400 mu M with linear coefficients of 0.9910 and 0.9925 for Cys and Hg2+ ion. The RA-AuNPs-based colorimetric assay represents the detection limits of 0.35 and 0.30 mu M for Cys and Hg2+ ion (3 sigma). This colorimetry assay is completed within 60 min, and successfully applied to detect Cys in urine and Hg2+ ion in water samples.