Sensitive detection of Au(III) using regenerative rhodamine B–functionalized chitosan nanoparticles

Chitosan nanoparticles functionalized with rhodamine B (called RB–CSN) were synthesized. Au(III) was adsorbed onto the surfaces of the RB–CSN through electrostatic interactions between the AuCl4− and the protonated amino groups in the RB–CSN. The nanoparticles with AuCl4− adsorbed onto them were easily separated from water by centrifugation. The maximum adsorption capacity of the RB–CSN was about 0.33 mmol/g. The self-assembled AuCl4− ions were adsorbed in very close proximities to the RB moieties in the RB–CSN, and this caused photo-induced electron transfer from the RB to the AuCl4− to occur efficiently. This meant that changes in the fluorescence of the RB–CSN were able to be used to determine the AuCl4− concentration more sensitively than were changes in the fluorescence of free RB. Under optimal conditions, the dynamic range over which RB–CSN can be used to detect Au(III) was 1.9 × 10−7 mol L−1 to 4.75 × 10−5 mol L−1. The detection limit was 1.52 × 10−8 mol L−1. The dual-functional RB–CSN material can be completely regenerated using a solution of 0.5 M thiourea and 0.1 M HCl. The reusable dual-functional material that was able to be used to both detect dissolved Au(III) and remove Au(III) from an aqueous solution.