Highly sensitive colorimetric detection of NH3 based on Au@Ag@AgCl core-shell nanoparticles

As an important component of the atmosphere, ammonia (NH₃) plays a very important role in maintaining the balance of environment. However, it is also one of the most toxic gases that can cause damage to the human respiratory system and mucous membranes even at low concentrations. As such, development of highly sensitive and selective NH₃ sensors is of high significance for environmental monitoring and health maintenance. Herein, we have synthesized Au@Ag@AgCl core-shell nanoparticles (NPs) by oxidative etching and precipitating Au@Ag core-shell NPs using FeCl₃ and further used them as optical probes for the colorimetric detection of NH₃. The sensing mechanism is based on the fact that the etching of NH₃ on AgCl and Ag shell leads to the variations of ingredients and core-to-shell ratio of the Au@Ag@AgCl NPs, thereby inducing noticeable spectral and color changes. By replacing the outmost layer of Ag with AgCl, not only is the stability of the sensor against oxygen significantly enhanced, but also is the sensitivity of the method improved. The method exhibits good linear relationship for the detection of NH₃ from 0 to 5000 μmol/L with the limit of detection of 6.4 μmol/L. This method was successfully applied to the detection of simulated air polluted by NH₃, indicating its practical applicability for environmental monitoring. This method shows great potential for on-site NH₃ detection particularly in remote area, where a simple, fast, low-cost, and easy-to-handle method is highly desirable.