Creatinine assembled on dithiobis(succinimidylpropionate) modified gold nanoparticles as a sensitive and selective colorimetric nanoprobe for silver ion detection

Abstract A sensitive and selective colorimetric assay for silver ion (Ag+) detection is demonstrated, based on creatinine (CRN) assembled on dithiobis(succinimidylpropionate) modified gold nanoparticles (DSP-AuNPs) as an optical probe. DSP was firstly modified on AuNPs to generate DSP-AuNPs through the highly efficient Au-S covalent interaction. Under pH 8.4 phosphate buffer, CRN can be assembled on DSP-AuNPs surface through the amine coupling reaction between the carboxyl group of DSP and the amino group of CRN, with the formation of an amide bond. Thus, CRN assembled on DSP-AuNPs denoted as DSP-AuNPs@CRN was used for Ag+ detection. The morphology of DSP-AuNPs@CRN was found to be highly dispersed and spherical particles with Dh of 41.5 ± 2.8 nm. When adding Ag+, progressive particle clustering of the nanoparticles was observed, Dh increased up to 324.7 ± 2.7 nm and naked eye color changed from red to blue-grey within 30 min, arising from particle aggregation. The absorption peak of dispersed and aggregated DSP-AuNPs@CRN was at 522 and 680 nm, respectively. The calibration curve plotted between the absorbance ratio (A680/A522) and Ag+ concentration was linear with two concentration ranges (0.50–3.00 µM and 3.00–35.00 µM Ag+). The assay detection limit of 0.13 µM is far below the USEPA maximum acceptable limit of Ag+ in drinking water at 0.93 μM. Finally, the assay has been successfully applied to Ag+ detection in water sample with good accuracy and precision.