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A molecular-gap device for specific determination of mercury ions.

Guo Z, Liu ZG, Yao XZ, Zhang KS, Chen X, Liu JH, Huang XJ - Sci Rep (2013)

Bottom Line: Despite great success, many inevitably encounter the interferences from other metal ions besides the complicated procedures and sophisticated equipments.Notably, the fabricated molecular-gap device shows a specific response toward Hg(2+) with a low detection limit actually measured down to 1 nM.Theoretical calculations demonstrate that the specific sensing mechanism greatly depends on the electron transport ability of glutathione dimer bridged by heavy metal ions, which is determined by its frontier molecular orbital, not the binding energy.

View Article: PubMed Central - PubMed

Affiliation: Nanomaterials and Environmental Detection Laboratory, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, P. R. China.

ABSTRACT
Specific determination/monitoring of trace mercury ions (Hg(2+)) in environmental water is of significant importance for drinking safety. Complementarily to conventional inductively coupled plasma mass spectrometry and atomic emission/absorption spectroscopy, several methods, i.e., electrochemical, fluorescent, colorimetric, and surface enhanced Raman scattering approaches, have been developed recently. Despite great success, many inevitably encounter the interferences from other metal ions besides the complicated procedures and sophisticated equipments. Here we present a molecular-gap device for specific determination of trace Hg(2+) in both standardized solutions and environmental samples based on conductivity-modulated glutathione dimer. Through a self-assembling technique, a thin film of glutathione monolayer capped Au nanoparticles is introduced into 2.5 μm-gap-electrodes, forming numerous double molecular layer gaps. Notably, the fabricated molecular-gap device shows a specific response toward Hg(2+) with a low detection limit actually measured down to 1 nM. Theoretical calculations demonstrate that the specific sensing mechanism greatly depends on the electron transport ability of glutathione dimer bridged by heavy metal ions, which is determined by its frontier molecular orbital, not the binding energy.

No MeSH data available.


Characterization.(a) High magnified TEM image of bare Au NPs. (b) High magnified TEM image of Au NPs capped with GSH (Au@GSH). 1–2 nm of GSH layer is clearly seen. (c) SEM image of two adjacent interdigital Au microelectrodes with self-assembled Au@GSH NPs, the inset corresponds to optical photo of the fabricated molecular-gap device. (d) Magnified SEM image of Au@GSH NPs between the interdigital Au microelectrodes.
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f2: Characterization.(a) High magnified TEM image of bare Au NPs. (b) High magnified TEM image of Au NPs capped with GSH (Au@GSH). 1–2 nm of GSH layer is clearly seen. (c) SEM image of two adjacent interdigital Au microelectrodes with self-assembled Au@GSH NPs, the inset corresponds to optical photo of the fabricated molecular-gap device. (d) Magnified SEM image of Au@GSH NPs between the interdigital Au microelectrodes.

Mentions: Fig. 2a and b show high magnified TEM images of bare Au NPs and Au@GSH NPs, respectively. For bare Au NPs, evidently, their surfaces are smooth without any modifiers. After modification of GSH, the outer of Au NPs are covered with a thin layer marked by red dash lines, which is be ascribed to a few of GSH molecules nonspecifically adsorbed their surface besides the GSH monolayer binding with Au NPs. Notably the thickness is about 1 ~ 2 nm, approximately equaling to the scale of a GSH molecular. Fig. 2c shows SEM image of Au@GSH NPs self-assembled between Au interdigital microelectrodes with the separated distance of 2.5 μm. It is seen that, with the complete evaporation of the solvent, Au@GSH NPs spread and closely packed together, the micro-gap electrodes are covered with a thin layer film consisted of numerous nanoparticles. From the magnified SEM image presented in Fig. 2d, these nanoparticles seem to be separated by numerous gaps with several nanometers. However, Au NPs are insulated by double molecular layers owing the existence of monolayer of GSH on their surfaces, which could be verified by the electrical measurements in the following part. These observations directly demonstrate the formation of molecular-gap between Au NPs through the monolayer of GSH on Au NPs surfaces. Additionally, it should be pointed out that, owing to the hydrophilicity of carboxylic groups of GSH exposed on the surface of Au NPs, poly(ethylene glycol) (PEG) dithiol is used to cross-link the Au NPs and stabilize the self-assembled film. From the optical photo shown in the inset of Fig. 2c, the fabricated device is portable, which is much smaller in comparison with a coin.


A molecular-gap device for specific determination of mercury ions.

Guo Z, Liu ZG, Yao XZ, Zhang KS, Chen X, Liu JH, Huang XJ - Sci Rep (2013)

Characterization.(a) High magnified TEM image of bare Au NPs. (b) High magnified TEM image of Au NPs capped with GSH (Au@GSH). 1–2 nm of GSH layer is clearly seen. (c) SEM image of two adjacent interdigital Au microelectrodes with self-assembled Au@GSH NPs, the inset corresponds to optical photo of the fabricated molecular-gap device. (d) Magnified SEM image of Au@GSH NPs between the interdigital Au microelectrodes.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3814579&req=5

f2: Characterization.(a) High magnified TEM image of bare Au NPs. (b) High magnified TEM image of Au NPs capped with GSH (Au@GSH). 1–2 nm of GSH layer is clearly seen. (c) SEM image of two adjacent interdigital Au microelectrodes with self-assembled Au@GSH NPs, the inset corresponds to optical photo of the fabricated molecular-gap device. (d) Magnified SEM image of Au@GSH NPs between the interdigital Au microelectrodes.
Mentions: Fig. 2a and b show high magnified TEM images of bare Au NPs and Au@GSH NPs, respectively. For bare Au NPs, evidently, their surfaces are smooth without any modifiers. After modification of GSH, the outer of Au NPs are covered with a thin layer marked by red dash lines, which is be ascribed to a few of GSH molecules nonspecifically adsorbed their surface besides the GSH monolayer binding with Au NPs. Notably the thickness is about 1 ~ 2 nm, approximately equaling to the scale of a GSH molecular. Fig. 2c shows SEM image of Au@GSH NPs self-assembled between Au interdigital microelectrodes with the separated distance of 2.5 μm. It is seen that, with the complete evaporation of the solvent, Au@GSH NPs spread and closely packed together, the micro-gap electrodes are covered with a thin layer film consisted of numerous nanoparticles. From the magnified SEM image presented in Fig. 2d, these nanoparticles seem to be separated by numerous gaps with several nanometers. However, Au NPs are insulated by double molecular layers owing the existence of monolayer of GSH on their surfaces, which could be verified by the electrical measurements in the following part. These observations directly demonstrate the formation of molecular-gap between Au NPs through the monolayer of GSH on Au NPs surfaces. Additionally, it should be pointed out that, owing to the hydrophilicity of carboxylic groups of GSH exposed on the surface of Au NPs, poly(ethylene glycol) (PEG) dithiol is used to cross-link the Au NPs and stabilize the self-assembled film. From the optical photo shown in the inset of Fig. 2c, the fabricated device is portable, which is much smaller in comparison with a coin.

Bottom Line: Despite great success, many inevitably encounter the interferences from other metal ions besides the complicated procedures and sophisticated equipments.Notably, the fabricated molecular-gap device shows a specific response toward Hg(2+) with a low detection limit actually measured down to 1 nM.Theoretical calculations demonstrate that the specific sensing mechanism greatly depends on the electron transport ability of glutathione dimer bridged by heavy metal ions, which is determined by its frontier molecular orbital, not the binding energy.

View Article: PubMed Central - PubMed

Affiliation: Nanomaterials and Environmental Detection Laboratory, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, P. R. China.

ABSTRACT
Specific determination/monitoring of trace mercury ions (Hg(2+)) in environmental water is of significant importance for drinking safety. Complementarily to conventional inductively coupled plasma mass spectrometry and atomic emission/absorption spectroscopy, several methods, i.e., electrochemical, fluorescent, colorimetric, and surface enhanced Raman scattering approaches, have been developed recently. Despite great success, many inevitably encounter the interferences from other metal ions besides the complicated procedures and sophisticated equipments. Here we present a molecular-gap device for specific determination of trace Hg(2+) in both standardized solutions and environmental samples based on conductivity-modulated glutathione dimer. Through a self-assembling technique, a thin film of glutathione monolayer capped Au nanoparticles is introduced into 2.5 μm-gap-electrodes, forming numerous double molecular layer gaps. Notably, the fabricated molecular-gap device shows a specific response toward Hg(2+) with a low detection limit actually measured down to 1 nM. Theoretical calculations demonstrate that the specific sensing mechanism greatly depends on the electron transport ability of glutathione dimer bridged by heavy metal ions, which is determined by its frontier molecular orbital, not the binding energy.

No MeSH data available.