Colorimetric detection of lysine using gold nanoparticles aggregation

A simple, reliable and sensitive colorimetric method for the detection of lysine was developed based on the use of citrate-stabilized gold nanoparticles (AuNPs). In acid media (pH = 3.0), AuNPs exhibited a sensitive color change from red to blue after the addition of lysine for 30 min at room temperature, which could directly be seen with the naked eye and monitored by UV-vis absorption spectroscopy. Results showed that the absorbance ratio (A680/A520) was linear for a lysine concentration in the range of 1 to 70 μM (r = 0.995), and the limit of detection was 0.8 μM at a signal-to-noise ratio of 3. This method also demonstrated excellent selectivity for lysine over other amino acids. For the analysis of lysine in food samples, precision and accuracy were checked.