Colorimetric and visual determination of dicyandiamide using gallic acid-capped gold nanoparticles

A new method is presented for the visual detection of dicyandiamide (DCD). Gold nanoparticles (AuNPs) capped with gallic acid (GA) were synthesized in a single step at room temperature, using GA as both the reducing agent and stabilizer. In the presence of DCD, the hydrogen-bonding interaction between GA and DCD induces the aggregation of AuNPs, associated with a color change from red to gray that can be observed with bare eye. DCD could be quantified by photometry as the red shift of the maximal absorption band is linearly related to the logarithm of concentration of DCD in the 0.1 to 500 mu M concentration range, with a regression coefficient of 0.9987 and a 80 nM detection limit (at an SNR of 3). The proposed method was successfully applied to the detection of DCD in spiked dairy samples.