Strip and test: Mercury revealed

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  • Published: May 1, 2012
  • Author: David Bradley
  • Channels: Atomic
thumbnail image: Strip and test: Mercury revealed

Mercurial contamination

Mercury revealed through strip test and

obvious visual pun.

A strip test for mercury ions in water samples offers results comparable with atomic absorption spectroscopy measurements, according to a team from Ningbo University, China.

Zhiyong Guo, Jing Duan, Fei Yang, Min Li, Tingting Hao, Sui Wang and Danyi Wei have developed a test strip based on gold nanoparticles functionalised with biotin-labelled and thiolated DNA to make them sensitive to mercury. The functionalization exploits the complex that forms between the DNA base thymine and mercury(II) ions resulting in a colour change in the strip that is highly sensitive and highly selective for the hazardous metal ions. Mercury ions represent an important environmental and health risk, especially given that they can accumulate in tissues and rise up through the food chain so readily. The metal ions have a particular affinity for sulfur-rich proteins and enzymes and so can disrupt numerous biochemical processes leading to organ dysfunction and central nervous system damage through high acute or chronic exposure. There are many techniques for the determination of mercury in aqueous samples including chromatography, inductively coupled plasma-mass spectrometry (ICP-MS), atomic absorption/emission spectrometry, cold vapour atomic absorption spectrometry (CVAAS), cold vapour atomic fluorescence spectrometry, electrochemiluminescence and other electrochemical methods. However, these require sophisticated instrumentation, highly trained technicians and usually laboratory conditions. An alternative sensor technology based on a simple strip that gives a visual cue to mercury contamination is needed.

Colour fast test

"One potential approach is the colorimetric method based on gold nanoparticles (AuNPs), which is extremely attractive, because it can be easily read out with the naked eye, in some cases at the point of use," the team says. They explain that they have made the necessary functionalised gold nanoparticles through a self-assembly process and then used a second thymine-rich DNA strand to form duplex DNA on the nanoparticle surfaces with thymine-Hg2+-thymine (THg2+T) coordination in the presence of mercury(II) in the nitrocellulose membrane of the strip as the test zone. "When mercury(II) ions were introduced into this system, they induced the two strands of DNA to intertwine by forming THg2+T bonds resulting in a red line at the test zone," the team explains. Under optimal conditions, the lower limit for detection of mercury(II) ions in an aqueous sample was just 3 nanomolar, the team adds. The US Environmental Protection Agency (EPA) defines 10 nM as the limit for safe drinking water.

AAS validation

To validate the new test strip, the Ningbo University team carried out a parallel analysis of pool water samples using cold vapour atomic absorption spectrometry. This "showed comparable results to those obtained from the strip test," the team adds. They suggest that the work should enable further research for the development of mercury detection and more specifically as a simple on-site screening tool for testing industrial, environmental and other samples without the need for expensive and specialist instrumentation. The team will report details in the May issue of the journal Talanta.

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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