Gold nanoparticles-based colorimetric determination of cationic surfactants in environmental water samples via both electrostatic and hydrophobic interactions

We report on a simple, rapid and sensitive colorimetric assay for the quantitation of cationic surfactants (CS+) in domestic effluent, municipal waste and surface water samples. The method is based on the aggregation of tartrate-capped gold nanoparticles (AuNPs) through both electrostatic and hydrophobic interactions that occur between CS+ and AuNPs. Aggregation results in a color change from pink to blue which is due to a shift in the localized surface plasmon resonance band. The detergent cetylpyridinium chloride (CPC) was chosen as a model compound for optimization of the method for determination of a CS+. Under optimized experimental conditions (pH 9.0; reaction time 5 min; 25 nM concentration of AuNPs), a linear calibration plot was obtained for quantitative determination of CPC, cetyltrimethylammonium bromide (CTAB), dodecyltrimethyl ammonium bromide (DTAB) in the range of 10-500, 10-200 and 10-300 ngmL(-1), respectively and the limit of detection was 3 ngmL(-1) for CPC, CTAB and DTAB.