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

Polyamine-capped gold nanorods (AuNRs) were developed as nanoprobes for localized surface Plasmon resonance (LSPR)-based simple, selective, and sensitive detection of Cu(2+) 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 Cu(2+) 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 Cu(2+) ion detection. A linear range from 1μM to 5mM and a detection limit (3σ/k) of 0.24μM were achieved in PBS. The concentration dependent shifts of longitudinal extinction peak of PEI-PSS-AuNRs notably results from the specific PEI-Cu(2+) 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 Cu(2+) sensing. Moreover, the developed probes were successfully used to detect Cu(2+) in river water, demonstrating their feasibility for analysis of surface water sample.