Au-ag quantum dot nanozyme identified for multi-mode fluorescent, UV–vis and intelligent RGB monitoring and removal of toxic Hg2+ and S2− in food samples

To conveniently monitor and remove toxic Hg 2+ and S 2− in food samples, Au Ag quantum-dot nanozyme (Au-Ag@FA QDs) was identified. The strong synergistic effect among folic acid (FA), Ag and Au endowed Au-Ag@FA QDs with superior peroxidase-mimic activity to accelerate 3,3′,5,5′-tetramethylbenzidine (TMB) redox with K m / V max of 0.28 mmol·L −1 /6.40 × 10 −8  mol·L −1 ·s −1 . Trace Hg 2+ or S 2− could selectively alter its peroxidase-like activity and inherent fluorescence performance, with obvious hyperchromic/“turn-on” fluorescent effect for Hg 2+ or hypochromic/“turn-off” one for S 2− . And red-green-blue (RGB) values analyzed from smartphones changed regularly with c Hg 2+ or c S 2− . Under the optimized conditions, Au-Ag@FA QDs were successfully applied for multi-mode UV–vis, fluorescent, and RGB monitoring of Hg 2+ or S 2− in food samples. The detection limits were 7.38 × 10 −7 /5.74 × 10 −8 /4.93 × 10 −6  g·L −1 and 1.99 × 10 −6 /4.48 × 10 −8 /5.79 × 10 −6  g·L −1 respectively. Importantly, over 93.8 % Hg 2+ or 90.5 % S 2− could be removed by simple centrifugal-separation after detection. The selective recognition mechanisms to Hg 2+ and S 2− were also proposed.