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    Highly Sensitive Electrochemical Sensor for Mercury(II) Ions by Using a Mercury-Specific Oligonucleotide Probe and Gold Nanoparticle-Based Amplification

    Year: 2009

    Journal: Anal. Chem., 2009, 81 (18), pp 7660–7666, 20100827

    Authors: Zhu Z. †‡, Su Y. †‡, Li J. ‡§, Li D. *‡, Zhang J. ‡, Song S. ‡, Zhao Y. §, Li G. *†, Fan C. ‡

    Last authors: Chunhai Fan

    Organizations: Department of Biochemistry and National Key Laboratory of Pharmaceutical Biotechnology, Nanjing University, Nanjing 210093, China, Laboratory of Physical Biology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China, and School of Life Sciences, Sichuan University, Chengdu 610064, China

    Country: China

    We report a highly sensitive electrochemical sensor for the detection of Hg2+ ions in aqueous solution by using a thymine (T)-rich, mercury-specific oligonucleotide (MSO) probe and gold nanoparticles (Au NPs)-based signal amplification. The MSO probe contains seven thymine bases at both ends and a “mute” spacer in the middle, which, in the presence of Hg2+, forms a hairpin structure via the Hg2+-mediated coordination of T−Hg2+−T base pairs. The thiolated MSO probe is immobilized on Au electrodes to capture free Hg2+ in aqueous media, and the MSO-bound Hg2+ can be electrochemically reduced to Hg+, which provides a readout signal for quantitative detection of Hg2+. This direct immobilization strategy leads to a detection limit of 1 μM. In order to improve the sensitivity, MSO probe-modified Au NPs are employed to amplify the electrochemical signals. Au NPs are comodified with the MSO probe and a linking probe that is complementary to a capture DNA probe immobilized on gold electrodes. We demonstrated that this Au NPs-based sensing strategy brings about an amplification factor of more than 3 orders of magnitude, leading to a limit of detection of 0.5 nM (100 ppt), which satisfactorily meets the sensitivity requirement of U.S. Environmental Protection Agency (EPA). This Au NPs-based Hg2+ sensor also exhibits excellent selectivity over a spectrum of interference metal ions. Considering the high sensitivity and selectivity of this sensor, as well as the cost-effective and portable features of electrochemical techniques, we expect this Au NPs amplified electrochemical sensor will be a promising candidate for field detection of environmentally toxic mercury.