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

In this work, a rapid, simple and sensitive colorimetric sensor for simultaneous (or respective) detection of Cr³⁺ and Pb²⁺ using tyrosine functionalized gold nanoparticles (AuNPs^Tyr) 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 AuNPs^Tyr 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 AuNPs^Tyr can be regnerated and recycled by removing Pb²⁺ and Cr³⁺. Even after 3 rounds, AuNPs^Tyr show almost the same A_580nm/A_520nm 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 AuNPs^Tyr 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.