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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.


Related in: MedlinePlus

Typical I-V plots and sensitivity and specifity toward Hg2+ by fabricated molecular gap device.(a–b) I-V curves for molecular gap devices before and after exposure to Zn2+ (1 mM) and Hg2+ (1 mM), respectively. The conductance is virtually unchanged after immersion in 1 mM solution of Zn2+, and results in a marked change in a 1 mM solution of Hg2+. (c) Real-time sensing curve under different concentration of Hg2+ for the molecular-gap device under a bias voltage of 0.1 V. (d) Specifity of the fabricated molecular-gap device. The concentration of all investigated metal ions is 1 mM; Rb and Ra are the resistance of the device before and after immersion, respectively.
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f3: Typical I-V plots and sensitivity and specifity toward Hg2+ by fabricated molecular gap device.(a–b) I-V curves for molecular gap devices before and after exposure to Zn2+ (1 mM) and Hg2+ (1 mM), respectively. The conductance is virtually unchanged after immersion in 1 mM solution of Zn2+, and results in a marked change in a 1 mM solution of Hg2+. (c) Real-time sensing curve under different concentration of Hg2+ for the molecular-gap device under a bias voltage of 0.1 V. (d) Specifity of the fabricated molecular-gap device. The concentration of all investigated metal ions is 1 mM; Rb and Ra are the resistance of the device before and after immersion, respectively.

Mentions: Since carboxylic acid group could interact with various metal ions17, we wonder whether the conductivity of the Au@GSH NPs film consisted numerous molecular-gaps is changed. Firstly, Zn2+ and Hg2+ are employed as examples. I-V curves are recorded before and after binding with Zn2+ and Hg2+, as shown in Fig. 3a and b, respectively. From Fig. 3a, after immersion in a 1 mM solution of Zn2+, the slop of I-V curve (red line) does not evidently increase in contrast to the black line of blank, implying that the conductance of the films is virtually unchanged. However, when being immersed into a 1 mM solution of Hg2+, it can be clearly observed that its conductivity is remarkably increased, inferring from the I-V curve (green line) shown in Fig. 3b. Enlightened by the above results, such a molecular-gap device could be potentially used to the detection of Hg2+. Under a certain bias voltage, the real-time response curve toward different concentration of Hg2+ has been performed, as depicted in Fig. 3c. From the inset, obvious sensing signal can be seen when the concentration of Hg2+ is down to 1 nM, indicating that the fabricated molecular-gap device with a very low detection limit actually measured. Relative to the blank, the flowing current gradually increases with the incensement of its concentration. Up to 0.1 mM, it is greatly changed. In order to demonstrate the positive sensing characteristics arised from GSH molecules, another film assembled with bare Au NPs linked with PEG dithiol has further been investigated. Different from the film consisted of bare Au NPs, its resistivity is very larger similar with that of Au@GSH NPs. The reason can be attributed that Au NPs is partly insulted by PEG dithiol molecules to some extent. The real-time sensing curve toward different concentration of Hg2+ is shown in Fig. S3 (Supplementary). Clearly, no response has been observed when the concentration is lower than 1 μM. Further increasing to 1 mM, a weak response can be seen. However, it can be neglected, compared with that of Au@GSH NPs film. It is suggested that the monolayer of GHS is very critical for the sensing properties of the fabricated molecular-gap device. Besides Hg2+ and Zn2+, other metal ions have also been explored carefully (Supplementary Fig. S4). We find that the responses of the molecular-gap device toward all investigated metal ions are not evident except for Hg2+. Even at their high concentration of 1 mM, it still shows no response. Based on the comparison of the sensitivity shown in Fig. 3d, it can be concluded that the fabricated molecular-gap device exhibits a specific selectivity toward metal ions and can be effectively employed for the determination of Hg2+ in the real water sample without any interferences from other metal ions.


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)

Typical I-V plots and sensitivity and specifity toward Hg2+ by fabricated molecular gap device.(a–b) I-V curves for molecular gap devices before and after exposure to Zn2+ (1 mM) and Hg2+ (1 mM), respectively. The conductance is virtually unchanged after immersion in 1 mM solution of Zn2+, and results in a marked change in a 1 mM solution of Hg2+. (c) Real-time sensing curve under different concentration of Hg2+ for the molecular-gap device under a bias voltage of 0.1 V. (d) Specifity of the fabricated molecular-gap device. The concentration of all investigated metal ions is 1 mM; Rb and Ra are the resistance of the device before and after immersion, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: Typical I-V plots and sensitivity and specifity toward Hg2+ by fabricated molecular gap device.(a–b) I-V curves for molecular gap devices before and after exposure to Zn2+ (1 mM) and Hg2+ (1 mM), respectively. The conductance is virtually unchanged after immersion in 1 mM solution of Zn2+, and results in a marked change in a 1 mM solution of Hg2+. (c) Real-time sensing curve under different concentration of Hg2+ for the molecular-gap device under a bias voltage of 0.1 V. (d) Specifity of the fabricated molecular-gap device. The concentration of all investigated metal ions is 1 mM; Rb and Ra are the resistance of the device before and after immersion, respectively.
Mentions: Since carboxylic acid group could interact with various metal ions17, we wonder whether the conductivity of the Au@GSH NPs film consisted numerous molecular-gaps is changed. Firstly, Zn2+ and Hg2+ are employed as examples. I-V curves are recorded before and after binding with Zn2+ and Hg2+, as shown in Fig. 3a and b, respectively. From Fig. 3a, after immersion in a 1 mM solution of Zn2+, the slop of I-V curve (red line) does not evidently increase in contrast to the black line of blank, implying that the conductance of the films is virtually unchanged. However, when being immersed into a 1 mM solution of Hg2+, it can be clearly observed that its conductivity is remarkably increased, inferring from the I-V curve (green line) shown in Fig. 3b. Enlightened by the above results, such a molecular-gap device could be potentially used to the detection of Hg2+. Under a certain bias voltage, the real-time response curve toward different concentration of Hg2+ has been performed, as depicted in Fig. 3c. From the inset, obvious sensing signal can be seen when the concentration of Hg2+ is down to 1 nM, indicating that the fabricated molecular-gap device with a very low detection limit actually measured. Relative to the blank, the flowing current gradually increases with the incensement of its concentration. Up to 0.1 mM, it is greatly changed. In order to demonstrate the positive sensing characteristics arised from GSH molecules, another film assembled with bare Au NPs linked with PEG dithiol has further been investigated. Different from the film consisted of bare Au NPs, its resistivity is very larger similar with that of Au@GSH NPs. The reason can be attributed that Au NPs is partly insulted by PEG dithiol molecules to some extent. The real-time sensing curve toward different concentration of Hg2+ is shown in Fig. S3 (Supplementary). Clearly, no response has been observed when the concentration is lower than 1 μM. Further increasing to 1 mM, a weak response can be seen. However, it can be neglected, compared with that of Au@GSH NPs film. It is suggested that the monolayer of GHS is very critical for the sensing properties of the fabricated molecular-gap device. Besides Hg2+ and Zn2+, other metal ions have also been explored carefully (Supplementary Fig. S4). We find that the responses of the molecular-gap device toward all investigated metal ions are not evident except for Hg2+. Even at their high concentration of 1 mM, it still shows no response. Based on the comparison of the sensitivity shown in Fig. 3d, it can be concluded that the fabricated molecular-gap device exhibits a specific selectivity toward metal ions and can be effectively employed for the determination of Hg2+ in the real water sample without any interferences from other metal ions.

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.


Related in: MedlinePlus