The fabrication of nanochain structure of gold nanoparticles and its application in ractopamine sensing

The illegal food additives including ractopamine and melamine throw a serious threat to human health. In this paper, the ractopamine and melamine were first used to form the nanochain structure of citrate-stabilized gold nanoparticles (AuNPs) with a convenient and inexpensive method. The fabricated nanochain structure consisting of several AuNPs was characterized by Scanning Electron Microscopy. A new longitudinal surface plasma resonance, which could be adjusted from visible to near infrared range, was observed in absorption spectra due to the aggregation of AuNPs. This could be well explained by Finite Different Time Domain algorithm theoretically. As confirmed by Fourier Transform Infrared Spectroscopy, the complex formed by hydrogen-bonding interaction between melamine and ractopamine could effectively promote the aggregation of AuNPs that was useful to develop the sensitivity and selectivity for the detection of ractopamine. Hence, the plasmonic coupling phenomenon of gold nanochain could be applied in bio-assay for ractopamine through the change of solution's color and optical absorption band with naked eye or absorption spectra. The linear range was broadened to (1.23×10^-7 M, 1.11×10^-6 M) and the limit of detection was extended to 4.10×10^-8 M (S/N=3). More importantly, this time-saving method will be promising in rapid and selective detection of β-agonist for clinical applications.