Porous Ag-Chitosan Nanospheres Bridged by Cysteine Residues for Colorimetric Sensing of Trace Hg²⁺

Abstract

To enhance the sensing performance of precious metal nanomaterials, porous Ag-chitosan nanospheres (AgNPs-cys-CS) were developed for the first time in this work. There was a strong coordination bonding interaction between the Ag nanospheres and the −SH groups in cysteine, accompanied by hydrogen bonds or esterification between the −OH groups in chitosan and the −COOH groups in cysteine. Porous Ag nanospheres and chitosan chains were bridged by cysteine residues. After its structure and properties were characterized in detail, we found that the AgNPs-cys-CS material expressed exclusive colorimetric recognition of Hg2+ with a color change from yellow to colorless. Under the optimized conditions, the partitioned linear range of c Hg 2+ was quite wide from 8.0 to 14 000.0 × 10–8 mol·L–1 and the detection limit was 1.2 × 10–9 mol·L–1, far below the restricted limit for the presence of Hg2+ in drinking water set by the World Health Organization. After detection, more than 92.8% of the Hg2+ in the samples was separated by a simple filtration process. The secondary pollution caused during the detection process was eliminated accordingly. The action mechanism was proposed to form silver amalgam on the surface of the AgNPs-cys-CS by virtue of the reducibility of chitosan.

Ag-β-Cyclodextrin-Graphene Oxide Ternary Nanostructures with Peroxidase-Mimicking Activity for Hg2+ Detection

“…Further, from its HR-TEM and EDS (Figure d), we could find the presence of the feeding elements Ag, C, and O in the as-prepared Ag-β-CD-GO. The (111) interplanar spacing of AgNPs at 2.29 Å was obviously found in HR-TEM (inset in Figure d) and well confirmed the construction of Ag nanoparticles.…”

“…In UV–vis spectra of Ag-β-CD-GO (Figure e), two absorbance peaks appear at 212 and 390 nm, accompanied by a shoulder at 298 nm. The absorbance at 390 nm results from the surface plasmon of AgNPs, , suggesting the production of Ag nanoparticles. The absorbance at 212 nm with a shoulder at 298 nm corresponds to π → π* and n → π* electron transitions of the graphene oxide matrix .…”

NiS Nanospheres Anchored onto a Graphene Oxide Substrate (NiS@GO) for Efficient Electrochemical Sensing of Trace Amounts of Silver Ions

“…The fringe spacing of 0.23 nm is attributed to the (111) inter-planar spacing of Ag nanoparticles. [57] All these observations confirm that Ag + ions have been adsorbed and reduced into nano Ag on the surface of NiS@GO/GCE as proposed in Figure 7c.…”

“…Specifically, the linear regression equation between peak current intensity (I (μA)) at 0.35 V and c Ag + was deduced to be I (μA) = 0.650 + 0.163 c (10 À 9 mol L À 1 ) (R 2 = 0.9936) with a linear range between 6.67 and 160 × 10 À 9 mol/L of Ag + (Figure 6b). Based on the definition, three times of average deviation (3σ) of I (μA) at 0.35 V in blank samples divided by the slope of the obtained standard curve, [57][58][59] the detection limit for Ag + is 1.76 × 10 À 10 mol/L, far below the permitted limit of 0.1 mg⋅L À 1 in drinking water set by World Health Organiza-tion (WHO). [9] The detection limit is better than those from other electrochemical sensors reported previously (Table 1).…”

Hydrogen Bond-Assisted Colorimetric Picomolar Level Detection of Hg2+ Ions in 100% Aqueous Solution

“…Very few reports on the colorimetric detection of Hg 2+ and Ag + using nanomaterial-based sensors viz. gold nanoparticles, − silver nanoparticles, − Pt nanocubes, and chromophoric polydentate ligands are available . Among them, only handful of materials were able to reach the picomolar level detection of Hg 2+ and Ag + ions. ,, Preparation of an organic dye molecule (D–A) with a higher molar extinction coefficient (ε) may improve the sensitivity in colorimetric detection.…”