A label-free SERRS-based nanosensor for ultrasensitive detection of mercury ions in drinking water and wastewater effluent

Abstract

Precisely probing mercury ions (Hg²⁺) is of essential importance to human health and environmental protection. Although numerous methods have been developed to detect Hg²⁺ in water, challenges still remain for rapid, accurate, and reliable detection of Hg²⁺ at the ppt level. In this study, a novel label-free Fe₃O₄@Ag based surface-enhanced Raman resonance scattering (SERRS) nanosensor has been developed for ultrasensitive and highly selective detection of Hg²⁺. The detection mechanism is on the basis of competitive binding interaction of Hg²⁺ and malachite green (MG) with nano-sliver on Fe₃O₄@Ag magnetic beads (MBs). In the absence of Hg²⁺, the Raman signal intensity of MG is significantly enhanced by the nano-silver when MG adsorbs on the nano-silver surface via one nitrogen atom. In the presence of Hg²⁺, the redox reaction occurring between zero-valent nano-silver and Hg²⁺ leads to the formation of a Ag/Hg amalgam at the Fe₃O₄@Ag surface, which prevents the adsorption of MG on the nano-silver surface. Thereby, the SERRS signal intensity of MG proportionally decreased with increasing Hg²⁺ concentration. Under optimized conditions, the proposed label-free nanosensor showed unprecedented Hg²⁺ detection sensitivity of 10 pM (2 ppt) with excellent selectivity. This simple sensor system can be directly applied for an inexpensive and easy-to-use monitoring method of Hg²⁺ in drinking water and wastewater treatment effluents that contains complicated organic and inorganic interferents.