Colorimetric determination of malachite green based on gold nanoparticles protected by fulvic acid

The development of rapid and sensitive malachite green (MG) detection methods is particularly important for food safety supervision and ecological protection. Using fulvic acid (FA) as a stabilizer and NaBH₄ as a reducing agent, ellipsoidal gold nanoparticles (AuNPs) with the average particle size of 5–20 nm were successfully prepared. Based on the interaction between fulvic acid protected gold nanoparticles (FA-AuNPs) and MG, the color change of FA-AuNPs from ruby red to blue was observed, the corresponding absorbance ratio change of gold nanoparticles at 611 nm and 529 nm (A611/A529) was also studied. Through the optimization of experimental conditions, the linear relationship between A611/A529 with the concentration of MG was established. The detection limit and linear range of this method were 0.02 μM and 0.04–2 μM, respectively. This method was successfully applied to detect malachite green in three different water samples with the recovery of 97.4–110.8%.