title: One-pot synthesis of two-sized clusters for ratiometric sensing of Hg2+.
abstract: This paper presents a discussion of a one-pot approach for preparing lyszoyme type VI (Lys VI) stabilized clusters, including small (Au7Ag and Au8) and large (Au24Ag) clusters, for ratiometric fluorescence sensing of Hg(2+). Our previous study (Chen and Tseng, Small 8 (2012) 1912) showed the formation of intermediate Au8 clusters in the conversion of Au(+)-Lys VI protein complexes to Au25 clusters. The presence of Ag(+) in the precursor solution slowed this conversion, thereby forming two-sized clusters. With an increase in Ag(+) content, a systematic blue shift in the first exciton absorption and fluorescence peaks indicated the formation of Au-Ag bimetallic clusters. The prepared Ag(+)/Au(3+) molar ratio of 2:8 resulted in the formation of two-sized clusters, with dual emission bands centered at 471 and 613 nm. After these clusters are separated by a membrane filter, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was used to determine the composition of Au24Ag clusters. By monitoring the intensity ratio of the two emission wavelengths, the solution consisting of Hg(2+)-insensitive small clusters (Au7Ag and Au8) and Hg(2+)-sensitive Au24Ag clusters exhibited a ratiometric fluorescence response toward Hg(2+), and provided a built-in correction for photobleaching; the limit of detection at a signal-to-noise ratio of three for Hg(2+) was estimated to be 1 nM. This probe was successfully applied to ratiometric fluorescence sensing of Hg(2+) in tap water.
authors.affiliation: Department of Chemistry, National Sun Yat-sen University, Taiwan; School of Pharmacy, College of Pharmacy, Kaohsiung Medical University, Taiwan.
authors.forename: Tzu-Heng
authors.initials: TH
authors.lastname: Chen
authors.forename: Chi-Yu
authors.initials: CY
authors.lastname: Lu
authors.forename: Wei-Lung
authors.initials: WL
authors.lastname: Tseng
mesh_terms: D060766:Drinking Water / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D006801:Humans; D057230:Limit of Detection; D008628:Mercury / Q000032:analysis*; D009113:Muramidase / Q000737:chemistry*; D059629:Signal-To-Noise Ratio; D012834:Silver / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D060766:Drinking Water; D014874:Water Pollutants, Chemical; D012834:Silver; D006046:Gold; D009113:Muramidase; D008628:Mercury
keywords: Fluorescence; Gold nanoclusters; Mercury(II); Ratiometric sensing