Hydrophilic Silver Nanoparticles for Hg(II) Detection in Water: Direct Evidence for Mercury–Silver Interaction

Abstract

In this work, the electronic and molecular structure, as well as the morphology, of innovative nanostructured materials whose optical properties respond to the presence of heavy metals in water samples was investigated. In particular, the here discussed silver nanoparticles (NPs) stabilized by a hydrophilic ligand (sodium 3-mercapto-1-propanesulfonate, 3MPS) are able to reveal the presence of mercury ions at ppm levels. The sensitivity of the proposed nanosensor to Hg(II) in 1−5 ppm range was ascertained by optical tests; then, the local chemistry and electronic structure of the nanostructured coordination compounds made of functionalized silver nanoparticles (NPs) and metal ions, and their correlation with the resulting nanoaggregates' shape and morphology, were investigated by state-of-the-art synchrotron radiation (SR)-induced spectroscopies and transmission electron microscopy (TEM). In particular, SR-induced X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) measurements allowed us to gather complementary information about the silver−mercury interaction, which is only partially mediated by the negatively charged 3MPS ligand, different from what was observed for analogous nanosensors applied to other bivalent heavy metal ions, for example, Co(II) and Ni(II). TEM morphological analysis sheds light on the structure of the AgNP-3MPS/Hg aggregates, revealing the formation of Ag/Hg alloy nanoparticles.

Silver Nanoparticles Functionalized by Fluorescein Isothiocyanate or Rhodamine B Isothiocyanate: Fluorescent and Plasmonic Materials

“…The first feature in the Ag3d spectrum (Ag3d5/2 BE = 367.84 eV) is associated with metallic silver and arises by the Ag atoms at the nanoparticles' core. The spin-orbit pair of very low intensity at higher BE values (Ag3d5/2 BE = 368.79 eV) is indicative for positively charged metal atoms, as expected for surface atoms interacting with the organic macromolecule [67]. The S2p spectra provide complementary information about the envisaged chemical interaction between the NCS functional groups of both dyes and the surface atoms of the silver clusters, as extensively discussed previously [57] for gold nanoparticles functionalized with RITC.…”

A Disposable Electrochemical Biosensor Based on Screen-Printed Carbon Electrodes Modified with Silver Nanowires/HPMC/Chitosan/Urease for the Detection of Mercury (II) in Water

“…Recently, there has been much interest in the development of improved technologies and devices for the detection and monitoring of Hg(II) ions in water, including nanomaterials and nanomaterials-based electrochemical methods [8][9][10][11]. Fast, sensitive, selective, and accurate monitoring of the presence of Hg(II) ions in the environment and drinking water samples is highly desirable [12].…”

Biocompatible Silver Nanoparticles: Study of the Chemical and Molecular Structure, and the Ability to Interact with Cadmium and Arsenic in Water and Biological Properties

“…The Cd3d and As3d core level spectra are also acquired and analyzed. The Cd3d signal (Figure 4a) has a single spin-orbit pair attributed to Cd(II) ions in coordination compounds (BE Cd3d 5/2 = 405.5 eV) [31][32][33], suggesting that the plasmonic shift observed for AgNPs in the presence of Cd ions could be related to the ability of Cd 2+ to coordinate the silver nanoparticles by interacting with the carboxylic functional groups of cysteine and/or citrate ligands, as already observed for other bivalent heavy metal ions (Co(II), Ni(II), Hg(II)) and extensively discussed in the literature [16,28]). Conversely, As3d SR-XPS spectrum (Figure 4b) shows two pairs of spin-orbit components indicative for As(III) in As 2 O 3 (As3d 5/2 BE = 45.0 eV) [31,34] and As(V) in As 2 O 5 (As3d 5/2 BE = 46.9 eV) [31,35], in atomic ratio As(V)/As(III) = 1,9/1; the As(III) partial oxidation to As(V) in water is not surprising, as reported in the literature [36]; however, the presence of arsenic oxides could explain the inability of As ions to coordinate the silver nanoparticles, and, consequently, the absence of a plasmonic response to the presence of this heavy metal ion.…”

“…The AgNPs/L-cys/citr are also tested in presence of 5, 10 and 25 ppm of As(III), but the LSPR band does not suffer any change in terms of intensity, peak position and band broadening. Figure 2b The Ag3d spectra (Figure 3a,b) are asymmetric at a high BE, a common feature in capped nanoparticles [28], indicating that at least two different kinds of silver atoms comprise the nanoparticle: the signal at lower BE values (Ag3d5/2 = 368.08 eV) is assigned to metallic silver atoms of the nanoparticle core, while the low-intensity (about 10% of the whole signal) spin-orbit pair at a higher BE (nearly 369 eV) is caused by positively charged silver atoms at the NP surface, interacting with the thiol end-group of L-cysteine [14]. The observed Ag(δ+) atomic % are in excellent agreement with the silver nanoparticles' mean sizes, as suggested by TEM and as will be discussed in the following.…”