Colorimetric determination and recycling of Hg²⁺ based on etching-induced morphology transformation from hollow AuAg nanocages to nanoboxes

Herein, we propose a selective and simple colorimetric sensing approach for the determination of Hg²⁺ ions based on bimetallic AuAg nanocages with partial hollow cavity and several pinholes on the wall, wherein the residual Ag atoms existing inside this AuAg nanocages can be directly etched by Hg²⁺ and the generated Hg depositing on inner surface of nanocages induces the morphology transformation from hollow AuAg nanocages to closed nanoboxes which consists of an AuAg shell and Hg core. This morphology transformation of “nanocage-to-nanobox” not only extends the detection range of Hg²⁺, but also cleans the Hg²⁺ in solutions by enriching it into the nanoboxes. With increasing Hg²⁺ concentrations, the blue shift of localized surface plasmon resonance (LSPR) peak position with multicolor changing from light-blue to light-brown is great for colorimetric determination of Hg²⁺. Under optimal conditions, the colorimetric sensing shows a linear response to Hg²⁺ ranging from 0.03 to 35 μM with a detection limit of 10 nM. Besides, interference study and real samples detection applying lake and tap water demonstrated that Hg²⁺ can be specifically and practically detected by utilizing this method.