Facile colorimetric detection of nitrite based on anti-aggregation of gold nanoparticles

Nitrite is often found in water and excess concentration of nitrite in water supplies is hazardous to the environment and human health. Nitrite detection in water samples has received increasing attention in recent years. In this work, a facile and selective method for the detection of nitrite (NO2-) using gold nanoparticles (AuNPs) was developed. 4-Aminothiophenol (4-ATP) can bridge citrate-stabilized AuNPs through Au-S and Au-N bonds. As a result, aggregation of AuNPs occurs. In contrast, in the presence of NO2-, the amine group of 4-ATP reacts readily with NO2- in acidic media, forming a diazonium cation. An increase in the concentration of NO2- alleviated AuNP aggregation by decreasing the number of free 4-ATP amine groups, and the solution color changed from purple to red. Therefore, the concentration of NO2- can be detected with the naked eye or with ultraviolet-visible spectroscopy, and the detection limits of NO2- were 10 mu M and 1 mu M, respectively. This method is not only cost-effective, but also avoids complicated surface modifications and tedious separation processes.