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Differentiation of biothiols from other sulfur-containing biomolecules using iodide-capped gold nanoparticles†
Abstract
We describe here a simple method based on the aggregation of gold nanoparticles (GNPs) to differentiate biothiols, such as cysteine, homocysteine, cysteinylglycine and glutathione from other sulfur-containing biomolecules, such as disulfide, thioether and thiocarbonyl molecules. The GNPs are capped with iodide ions (I−), which react with the GNPs to form a chemisorbed compact layer. The aggregation of the GNPs could be induced by biothiols, but not by other sulfur-containing biomolecules and uric acid, ascorbic acid, glucose, and bovine serum albumin. The added iodide exhibits both a stabilizing effect and salt effect on the aggregation of GNPs. The significance of these two opposite effects is dependent on the concentration of iodide and the binding ability of biothiols on the GNPs. The combination of the two effects leads to quite different aggregation kinetics of GNPs from that with other halide (chloride or bromide) ions which exhibit only the salt effect. Compared to other surfactants-capped GNPs, the iodide-capped GNPs are unique with a strong and compact adsorbed layer with small steric hindrance, which accounts for the selective response towards biothiols.
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