Polyamine-capped gold nanorod as a localized surface Plasmon resonance probe for rapid and sensitive copper(II) ion detection

• Polyamine-capped gold nanorods were developed as LSPR nanoprobes for Cu2+ detection.
• LSPR shift results from Cu2+-induced dielectric changes of PEI on AuNRs.
• Cu2+ in lab buffer and river water was successfully analyzed with the nanoprobes.
• The LSPR sensor is simple but capable of analysis of Cu2+ in various real samples.

Polyamine-capped gold nanorods (AuNRs) were developed as nanoprobes for localized surface Plasmon resonance (LSPR)-based simple, selective, and sensitive detection of Cu2+ ions. Poly(sodium-4-styrenesulfonate) (PSS) and polyethylenimine (PEI) was successively adsorbed on the positively charged AuNRs via electrostatic adsorption, resulting in polyamine-capped AuNRs (called “PEI–PSS–AuNRs” thereafter), in which PEI offered bifunctions of providing sufficient positive charges and static hindrance to ensure stability of the AuNRs and serving as a Cu2+ ion recognition molecule via specific chelation. The as-prepared PEI–PSS–AuNRs were characterized by UV–vis spectroscopy, zeta potential analyzer, and transmission electron microscopy (TEM). Experimental results show that the polyelectrolytes PSS and PEI have been successfully adsorbed on AuNRs. The PEI–PSS–AuNRs were then employed as nanoprobes for Cu2+ ion detection. A linear range from 1 μM to 5 mM and a detection limit (3σ/k) of 0.24 μM were achieved in PBS. The concentration dependent shifts of longitudinal extinction peak of PEI–PSS–AuNRs notably results from the specific PEI–Cu2+ chelation-induced changes of dielectric property of polyelectrolyte film attached on nanoprobes. The negligible interference from other metal ions demonstrates good selectivity of the PEI–PSS–AuNRs for Cu2+ sensing. Moreover, the developed probes were successfully used to detect Cu2+ in river water, demonstrating their feasibility for analysis of surface water sample.

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