Detection and removal of mercury and lead ions by using gold nanoparticle-based gel membrane

Abstract

This paper describes the use of two types of bovine serum albumin (BSA)-capped 14.2 nm diameter gold nanoparticles (Au NPs) for the separate detection of mercury (Hg²⁺) and lead (Pb²⁺) ions in highly saline media. The BSA-capped Au NPs were stable in solutions containing up to 500 mM NaCl. Introduction of BSA to a solution of rhodamine 6G (R6G) and 3-mercaptopropionic acid (MPA)-modified Au NPs (R6G/MPA–Au NPs) provided a R6G/MPA–Au NP@BSA probe for the sensing of Hg²⁺ ions. We also used BSA-capped Au NPs to detect Pb²⁺ ions through a mechanism based on Pb²⁺ ions accelerating the leaching rate of Au NPs in the presence of thiosulfate (S₂O₃²⁻) and 2-mercaptoethanol (2-ME). The resulting deposition of Hg²⁺ ions onto the Au NPs induced the release of R6G from the surfaces of the Au NPs, causing increased fluorescence from the R6G/MPA–Au NP@BSA solution. The Pb²⁺ ions accelerated the dissolution of the 2-ME/S₂O₃²⁻–Au NPs@BSA into solution, leading to dramatic decreases in the absorption. These two Au NP-based probes were highly sensitive (LOD ≈ nM) and selective (over 100-fold against other metal ions) toward Hg²⁺ or Pb²⁺ ions. We validated the practicality of these two probes through analyses of seawater and urine samples. We also developed a simple gel-based membrane for removal and sensing of Hg²⁺ or Pb²⁺ in aqueous solutions. The agarose gel was used to trap BSA-Au NPs, leading to the preparation of a nanocomposite film of Au NPs@BSA-decorated agarose gel membrane (Au NPs@BSA/AGM) for removing Hg²⁺ or Pb²⁺ in solution. In addition, R6G/MPA–Au NP@BSA-trapped agarose gel membrane (R6G/MPA–Au NP@BSA/AGM) and 2-ME/S₂O₃²⁻–Au NPs@BSA/AGM allowed for the rapid and simple detection of Hg²⁺ and Pb²⁺, respectively.