Colorimetric Aptasensor for Detection of Malachite Green in Fish Sample Based on RNA and Gold Nanoparticles

A facile colorimetric aptasensor based on unmodified gold nanoparticles (AuNPs) for rapid, highly sensitive and selective detection of malachite green (MG), one of triphenylmethane dyes and antibiotics, was successfully developed. Malachite green RNA aptamer having the binding ability with high affinity and specificity would be the ideal recognition receptor for MG. RNA aptamer can adsorb on the AuNPs and protect AuNPs against salt-induced aggregation. When malachite green were added in a solution, aggregation of AuNPs was specifically induced by desorption of aptamer from the surface of gold nanoparticles as the formation of aptamer-target complex. Therefore, the salt could trigger AuNP aggregate and the solution color changed from red to blue. The solution colors and absorbance were related with the concentrations of MG, and a well linear relationship in the wide range was obtained. The detection limit of MG was down to 15.95 nM. This colorimetric method was better than other traditional methods in terms of its reduced detection time, simple signal generation, high selectivity, lower detection limit, and observation with the naked eye. The proposed one-step, label-free method was successfully used to determine MG in actual fish samples. The high recoveries of MG in fish sample detection were satisfied.