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    • In spite of the impressive progress made in DNA

    2021-10-15

    In spite of the impressive progress made in DNA glycosylase assays in recent years, few of them have clearly been viable candidates for further development and implementation in biomedical research and clinical practice. Future research efforts should be devoted to devising assays with improved performance and without involving complex procedures for in vivo uses. One possible approach is to couple nanomaterials to single-step amplification schemes. Another plausible approach is to couple DNA glycosylase assays to chemoprevention measures through the use of chemopreventive agents since prevention is more important than detection and recovery. The main effects of chemopreventive agents include suppression/retardation or reversal of carcinogenic effect [98]. More investigative studies could be carried out via in vivo assays of specific DNA glycosylases to have a more accurate understanding of how they work. Hence, by analyzing the mechanism and effect of chemopreventive agents, we can then further expand on these assays. By coupling to the knowledge from chemoprevention, we will be able to create biochemical tools and discover novel drugs that can keep these carcinogens and mutagens at bay, thereby achieving the ultimate goal of improving human health. In view of the rapid progress made in a relatively short period of time, the outlooks of DNA glycosylase assays undoubtedly remain positive and wide-spread applications in fundamental research and clinical practice are realizable in future.
    Acknowledgements This work is supported by the Ministry of Education under the grant No. MOE-2014-T2-081.
    Introduction DNA damages may be caused by a great deal of physical or chemical factors (e.g., ultraviolet radiation, ionizing radiation and chemical mutagens), and serious consequences like gene mutation and canceration may arise [1,2]. 8-oxoguanosine (8-oxoG) is the major DNA trpv4 damage, which produces a structural transformation and induces G: C to A: T transversion [3]. Due to the strong mutagenic effect, 8-oxoG has been regarded as an indicator of oxidative damage in tumorigenesis [4,5]. Human 8-oxoguanine DNA glycosylase 1 (hOGG1) is a DNA glycosidase with AP lyase activity, which recognizes and removes 8-oxoG for the repair of DNA damage [6]. Therefore, hOGG1 is often used as a tumor marker in early clinical diagnosis [7]. Development of sensitive and accurate methods for the detection of hOGG1 is extremely important and in urgent need for evaluating the susceptibility of cancers. So far, several techniques have already been applied for hOGG1 assay, including capillary electrophoresis [8], radioactive assay [9], high-performance liquid chromatography (HPLC) [10], colorimetry [11], fluorescence [12], and mass spectrometry [13]. However, those methods usually require sophisticated instruments, complicated procedures and hazardous materials like radioactive reagents, which limit their practical applications. Furthermore, the sensitivity is generally unsatisfactory. Thus, the development of novel analytical methods is absolutely necessary and is still a great challenge. Electrochemical or photoelectrochemical techniques have attracted great concerns due to the advantages like easy operability, simple instrumentation, low cost and on-site detection. For example, Zhang et al. achieved sensitive and selective detection of 8-oxo-7,8-dihydro-2′-deoxyguanosine in double-stranded DNA films based on the spermine-biotin conjugate [14]. In addition, ratiometric electrochemical systems have been demonstrated to possess wider detection ranges and higher sensitivity [[15], [16], [17]], which have already been used for the detection of metal ions [18], nucleic acids [19], and proteins [20]. However, there is no report on ratiometric electrochemical sensing of hOGG1 currently.
    Experimental
    Results and discussion In this contribution, we focus our work on developing a novel ratiometric electrochemical biosensor for the detection of hOGG1 coupling hybridization chain reaction (HCR) assisted enzyme-free amplification. The working principle is shown in Scheme 1. First, DNA probe a is modified on the electrode surface via gold‑sulfur interaction. Next, probe b labeled with ferrocene (Fc) is attached by hybridization with probe a. Significant electrochemical response of Fc could be obtained. However, hOGG1 can specifically recognize 8-oxoG site and cleave probe b, which is then released from the electrode surface. Electrochemical signal of Fc is thus decreased. Supramolecular structures may always be used to enhance signals [21]. In this work, target initiated HCR is designed and its supramolecular product adsorbs a large number of [Ru(NH3)6]3+ molecules to report the second electrochemical signal. Briefly, single-stranded probe a produced by hOGG1 hybridizes with probe c, which triggers the hybridization with probe d and e in succession. HCR is thus occurred on the electrode surface and the adsorbed [Ru(NH3)6]3+ molecules result in an amplified voltammetric peak current. By analyzing the variations of Fc and [Ru(NH3)6]3+ signals, we could determine hOGG1 activity sensitively. The proposed method may have a great potential in biomedical researches and early clinical diagnostics.