Recyclable colorimetric sensor of Cr and Pb 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 Cr and Pb using tyrosine functionalized gold nanoparticles (AuNPs) 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 Cr and Pb. Upon the addition of Cr or Pb (a combination of them), the color of AuNPs 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 can be regnerated and recycled by removing Pb and Cr. Even after 3 rounds, AuNPs show almost the same A/A value for the assays of Pb and Cr, 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 aggregated by Cr or Pb (a combination of them) show excellent selectivity compared to other metal ions (Cr, Pb, Fe,Cu,Zn,Cr,Ni,Co,Hg,Mn,Mg,Ca,Cd). More importantly, the developed sensor manifests good stability at room temperature for 3months, which has been successfully used to determine Cr and Pb in the real water samples with a high sensitivity.