Colorimetric and visual read-out determination of cyanuric acid exploiting the interaction between melamine and silver nanoparticles

We present two colorimetric procedures for the determination of cyanuric acid, using silver nanoparticle-based (AgNPs) probes. The first is making use of melamine-modified AgNPs which bind to cyanuric acid through hydrogen bonding to form a large conjugate network that enhances the aggregation of AgNPs to produce an absorbance peak at 640 nm and a green coloration. In the second assay, melamine is directly added to the sample in order to form a stable complex with cyanuric acid. AgNPs are then added, resulting in the formation of an absorbance peaking at 525 nm and a color change from green (blank sample) to purple or orange-red as a function of cyanuric acid concentration. Matrix effects, that originate from the interaction of alkaline earth metals with the charged surface of the AgNPs, are mitigated through a matrix-matched calibration. In this manner, spectral transitions can be selectively attributed to the concentration of cyanuric acid, which can be even visually quantified at low mg L-1 levels with minimum sample pre-treatment and without sophisticated instrumentation.