Recyclable colorimetric sensor of Cr3+ and Pb2+ ions simultaneously using a zwitterionic amino acid modified gold nanoparticles.

In this work, a rapid, simple and sensitive colorimetric sensor for simultaneous (or respective) detection of Cr3+ and Pb2+ using tyrosine functionalized gold nanoparticles (AuNPsTyr) has been developed. Tyrosine, a natural and zwitterionic amino acid, could be as a reducing and capping agent to synthesise AuNPs and allow for the simultaneous and selective detection of Cr3+ and Pb2+. Upon the addition of Cr3+ or Pb2+ (a combination of them), the color of AuNPsTyr solution changes from red to blue grey and the characteristic surface plasmon resonance (SPR) band is red-shifted to 580nm due to the aggregation of AuNPs. Interestingly, the aggregated AuNPsTyr can be regnerated and recycled by removing Pb2+ and Cr3+. Even after 3 rounds, AuNPsTyr show almost the same A580nm/A520nm value for the assays of Pb2+ and Cr3+, indicating the good recyclability of the colorimetric sensor. The responding time (within 1min) and sensitivity of the colorimetric sensor are largely improved after the addition of 0.1M NaCl. Moreover, the AuNPsTyr aggregated by Cr3+ or Pb2+ (a combination of them) show excellent selectivity compared to other metal ions (Cr3+, Pb2+, Fe2+,Cu2+,Zn2+,Cr6+,Ni2+,Co2+,Hg2+,Mn2+,Mg2+,Ca2+,Cd2+). More importantly, the developed sensor manifests good stability at room temperature for 3months, which has been successfully used to determine Cr3+ and Pb2+ in the real water samples with a high sensitivity.