Hg2+-mediated aggregation of gold nanoparticles for colorimetric screening of biothiols

Abstract

In this work, we report a colorimetric assay for the screening of biothiols including glutathione (GSH), cysteine (Cys), and homocysteine (Hcys) based on Hg²⁺-mediated aggregation of gold nanoparticles (AuNPs). Hg²⁺ can induce aggregation of thiol-containing naphthalimide (1) capped AuNPs due to the cross-linking interactions from the resulting “thymine–Hg²⁺–thymine” (T–Hg²⁺–T) analogous structure. When Hg²⁺ is firstly treated with biothiols, followed by mixing with 1-capped AuNPs suspension, AuNPs undergo a transformation from an aggregation to a dispersion state depending on the concentration of biothiols. This anti-aggregation or re-dispersion of AuNPs is due to the higher affinity of Hg²⁺ for biothiols relative to compound 1. The corresponding color variation in the process of anti-aggregation of AuNPs can be used for the quantitative screening of biothiols through UV-vis spectroscopy or by the naked eye. Under optimized conditions, a good linear relationship in the range of 0.025–2.28 μM is obtained for GSH, 0.035–1.53 μM for Cys, and 0.040–2.20 μM for Hcys. The detection limits of this assay for GSH, Cys, and Hcys are 17, 9, and 18 nM, respectively. This colorimetric assay exhibits a high selectivity and sensitivity with tunable dynamic range. The proposed method has been successfully used in the determination of total biothiol content in human urine samples.