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In this work, a rapid, simple and sensitive colorimetric sensor for simultaneous (or respective) detection of Cr 3 + and Pb 2 + 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 Cr 3 + and Pb 2 + . Upon the addition of Cr 3 + or Pb 2 + (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 580 nm due to the aggregation of AuNPs. Interestingly, the aggregated AuNPs Tyr can be regnerated and recycled by removing Pb 2 + and Cr 3 + . Even after 3 rounds, AuNPs Tyr show almost the same A 580 nm / A 520 nm value for the assays of Pb 2 + and Cr 3 + , indicating the good recyclability of the colorimetric sensor. The responding time (within 1 min) and sensitivity of the colorimetric sensor are largely improved after the addition of 0.1 M NaCl. Moreover, the AuNPs Tyr aggregated by Cr 3 + or Pb 2 + (a combination of them) show excellent selectivity compared to other metal ions (Cr 3 + , Pb 2 + , Fe 2 + ,Cu 2 + ,Zn 2 + ,Cr 6 + ,Ni 2 + ,Co 2 + ,Hg 2 + ,Mn 2 + ,Mg 2 + ,Ca 2 + ,Cd 2 + ). More importantly, the developed sensor manifests good stability at room temperature for 3 months, which has been successfully used to determine Cr 3 + and Pb 2 + in the real water samples with a high sensitivity. [ABSTRACT FROM AUTHOR]