The detection of copper ions based on photothermal effect of cysteine modified Au nanorods

- The assembly process based on CYS-Au NRs at different pH show different aggregation behaviors.
- The feasible detection is highly sensitive to sensing Cu2+ in weak acidic medium.
- The photothermal conversion efficiency of Au NRs is relation with the assembly mode induced by Cu2+.

The cysteine (CYS)-stimulated aggregation of Au nanorods (NRs) is used as an auxiliary reporting system for the optical detection of copper ions. CYS-Au NRs show end-to-end and side-by-side assembly at strong acidic and basic condition, and corresponding LSPR peaks shift to red or blue. However, Cu2+ can readily induce the end-to-end assembly of CYS-Au NRs based on the coordination between Cu2+ and CYS at weak acidic condition (pH 5). The assembly of Cu2+-CYS-Au make the decrease of LSPR peak at 800 nm and appear a new peak at 1050 nm, which reduce their photothermal conversion efficiency under 808 nm laser irradiation. The different photothermal conversion efficiency has relation with the temperature change of Au NRs solution. So, a new nanosensor for detecting Cu2+ is developed based on the varied photothermal effect. Different from colorimetric detection for Cu2+, the sensor of photothermal effect is more sensitive to low concentration of Cu2+. It shows high sensitivity and selectivity. Here, the detection limit for Cu2+ is 5 nM.