Colorimetric detection of ractopamine and salbutamol using gold nanoparticles functionalized with melamine as a probe

A highly selective and sensitive method is developed for colorimetric detection of ractopamine and salbutamol using gold nanoparticles (AuNPs) functionalized with melamine (MA), respectively. The presence of these β-agonists induces the aggregation of gold nanoparticles through hydrogen-bonding interaction that was accompanied by a distinct change in color and optical properties, which could be monitored by a UV–vis spectrophotometer or even naked eyes. This process caused a significant decrease in the absorbance ratio (A670 nm/A520 nm) of melamine–gold nanoparticles (MA–AuNPs), and the color changed from wine red to blue. The systems exhibited a wide liner range, from 1×10−10 M to 5×10−7 mol/L with a correlation coefficient of 0.995 for ractopamine, and 1×10−10 M to 1×10−5 mol/L with a correlation coefficient of 0.996 for salbutamol, with measuring the absorbance ratio (A670 nm/A520 nm). The detection limit of these β-agonists is as low as 1×10−11 mol/L. Particularly, the developed method has been applied to the analysis of real swine feed samples and has achieved satisfactory results.