Colorimetric Assay for Determination of Lead (II) Based on Its Incorporation into Gold Nanoparticles during Their Synthesis

In this report, we present a new method for visual detection of Pb(2+). Gold nanoparticles (Au-NPs) were synthesized in one step at room temperature, using gallic acid (GA) as reducer and stabilizer. Pb(2+) is added during the gold nanoparticle formation. Analysis of Pb(2+) is conducted by a dual strategy, namely, colorimetry and spectrometry. During Au-NPs synthesis, addition of Pb(2+) would lead to formation of Pb-GA complex, which can induce the aggregation of newly-formed small unstable gold nanoclusters. Consequently, colorimetric detection of trace Pb(2+) can be realized. As the Pb(2+) concentration increases, the color turns from red-wine to purple, and finally blue. This method offers a sensitive linear correlation between the shift of the absorption band (Δλ) and logarithm of Pb(2+) concentration ranging from 5.0 × 10(−8) to 1.0 × 10(−6) M with a linear fit coefficient of 0.998, and a high selectivity for Pb(2+) detection with a low detection limit down to 2.5 × 10(−8) M.