A highly sensitive colorimetric sensor based on the aggregation of gold nanoparticles (Au NPs) and a smartphone camera as detector is reported for the determination of cyromazine. In the presence of cyromazine, a decrease in the characteristic SPR absorbance peak of Au NPs is observed at 520 nm. A color change in the solution of Au NPs was observed from burgundy to purple and then to blue gray with a red shift of the absorbance...