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 x 10(-7) mol L-1 to 4.75 x 10(-5) mol L-1. The detection limit was 1.52 x 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. (C) 2016 Elsevier B.V. All rights reserved.