Analytical Chemistry Chemical Cytometry Quantitates Superoxide

Anal. Chem. 2010, 82, 6830–6837
Colorimetric Sensing of Silver(I) and Mercury(II)
Ions Based on an Assembly of Tween 20-Stabilized
Gold Nanoparticles
Cheng-Yan Lin, † Cheng-Ju Yu, † Yen-Hsiu Lin, † and Wei-Lung Tseng* ,†,‡
Department of Chemistry, National Sun Yat-sen University, Taiwan, and National Sun Yat-sen University-Kaohsiung
Medical University Joint Research Center, Kaohsiung, Taiwan
We have developed a rapid and homogeneous method for
the highly selective detection of Hg 2+ and Ag + using
Tween 20-modified gold nanoparticles (AuNPs). Citrate
ions were found to still be adsorbed on the Au
surface when citrate-capped AuNPs were modified with
Tween 20, which stabilizes the citrate-capped AuNPs
against conditions of high ionic strength. When citrate
ions had reduced Hg 2+ and Ag + to form Hg-Au alloys
and Ag on the surface of the AuNPs, Tween 20 was
removed from the NP surface. As a result, the AuNPs
were unstable under a high-ionic-strength solution,
resulting in NP aggregation. The formation of Hg-Au
alloys or Ag on the surface of the AuNPs was demonstrated
by means of inductively coupled plasma mass
spectroscopy and energy-dispersive X-ray spectroscopy.
Tween 20-AuNPs could selectively detect Hg 2+ and
Ag + at concentrations as low as 0.1 and 0.1 µM inthe
presence of NaCl and EDTA, respectively. Moreover,
the probe enables the analysis of AgNPs with a minimum
detectable concentration that corresponds to 1
pM. This probe was successfully applied to detect Hg 2+
in drinking water and seawater, Ag + in drinking water,
and AgNPs in drinking water.
Interest in monitoring toxic metal ions in aquatic ecosystems
continues because these contaminants adversely affect the environment
and have serious medical effects. 1 Silver and mercury
are two of the most hazardous metal pollutants, and they are
widely distributed in ambient air, water, soil, and even food. 2,3
For example, silver can inactivate sulfhydryl enzymes and accumulate
in the body, 4 and mercury exposure can damage a
variety of organs and the immune system. 5 Current approaches
to detecting these two metal ions include inductively coupled
* To whom correspondence should be addressed. Fax: 011-886-7-3684046.
E-mail: tsengwl@mail.nsysu.edu.tw.
† Department of Chemistry, National Sun Yat-sen University.
‡ National Sun Yat-sen University-Kaohsiung Medical University Joint Research
Center.
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6830 Analytical Chemistry, Vol. 82, No. 16, August 15, 2010
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the selective detection of Ag + or Hg 2+ in aqueous solutions.
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DNA probe preparation. Recently, gold nanoparticles (AuNPs)
have become another emerging material for sensing Hg 2+ or
Ag + , because they have a high extinction coefficient in the
visible region and behavior that depends on the interparticle
distance. When the distances between the AuNPs become less
than the average particle diameter, the color of the AuNPs
changes from red to purple. Because of the coordination
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AuNPs have been used for colorimetric sensing of Hg 2+ . 20-22
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10.1021/ac1007909 © 2010 American Chemical Society
Published on Web 07/16/2010