Picomolar selective detection of mercuric ion (Hg2 + ) using a functionalized single plasmonic gold nanoparticle

Abstract

A highly sensitive method for the selective detection and quantification of mercuric ions (Hg2 + ) using single plasmonic gold nanoparticle (GNP)-based dark-field microspectroscopy(DFMS) is demonstrated. The method is based on the scattering property of a single GNPthat is functionalized with thiolated molecules, which is altered when analytes bind to thefunctionalized GNP. The spectral resolution of the system is 0.26 nm and a linear response toHg2 + was found in the dynamic range of 100 pM–10 µM. The methodpermits Hg2 + to be detected at the picomolar level, which is a remarkable reduction in the detectionlimit, considering the currently proscribed Environmental Protection Agency regulationlevel (10 nM, or 2 ppb) and the detection limits of other optical methods for detectingHg2 + (recently approx.1–10 nM). In addition, Hg2 + can be sensitively detected in the presence ofCd2 + ,Pb2 + ,Cu2 + ,Zn2 + andNi2 + , which do not interfere with the analysis. Based on the findings reported herein, it islikely that single-nanoparticle-based metal ion sensing can be extended to thedevelopment of other chemo- and biosensors for the direct detection of specifictargets in an intracellular environment as well as in environmental monitoring.