DNA methyltransferase (MTase) plays an important role in many biological processes and has been recognized as a predictive cancer biomarker far before other signs of malignancy and a therapeutic target in cancer treatment. Thus simple and sensitive determination of DNA MTase activity is urgently required. The commercially available glucometer is considered as the most successful point-of-care (POC) sensor up to date, and researchers extend its application in monitoring different types of targets rather than only glucose. Here, we developed a simple strategy for the sensitive detection of the DNA MTase (using M.SssI as an example) activity by using a glucometer as the signal transducer. A S1/S2 hybrid probe was designed including a specific recognition sequence for both DNA MTase and restriction endonuclease, and a complementary sequence for biotin-S3. Firstly, the S1/S2 hybrid probe was self-assembled on the gold electrode and methylated by M.SssI MTase to form the methylated dsDNA. Then, HpaII endonuclease specifically cleaved the residue of the unmethylated dsDNA. Subsequently, biotin-S3 hybridized with the overhang sequence of the methylated dsDNA. Finally, the biotin tag was successively combined with streptavidin (STV) and biotin-invertase. The invertase efficiently catalyzed the hydrolysis of sucrose to generate abundant glucose, which led to an amplified response of glucometer. This strategy could detect DNA MTase activity as low as 0.3 U mL-1 with good selectivity against other two cytosine MTases (HaeIII MTase and AluI MTase), and be successfully applied for screening the DNA MTase inhibitors (5-azacytidine and 5-aza-2'-deoxycytidine), implying our proposed method holds great promising application in early cancer diagnosis and therapeutics.

中文翻译：

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商用血糖仪作为信号传感器，用于简单评估 DNA 甲基转移酶活性和抑制剂筛选

DNA 甲基转移酶 (MTase) 在许多生物过程中发挥着重要作用，并且远早于其他恶性肿瘤迹象和癌症治疗中的治疗靶点，已被认为是一种预测性癌症生物标志物。因此，迫切需要对 DNA MTase 活性进行简单而灵敏的测定。市售血糖仪被认为是迄今为止最成功的即时 (POC) 传感器，研究人员将其应用扩展到监测不同类型的目标，而不仅仅是血糖。在这里，我们开发了一种简单的策略，通过使用血糖仪作为信号传感器来灵敏检测 DNA MTase（以 M.SssI 为例）活性。设计了一个 S1/S2 杂交探针，包括 DNA MTase 和限制性内切核酸酶的特异性识别序列，和生物素-S3的互补序列。首先，S1/S2杂交探针在金电极上自组装，通过M.SssI MTase甲基化形成甲基化dsDNA。然后，HpaII 核酸内切酶特异性切割未甲基化 dsDNA 的残基。随后，生物素-S3 与甲基化 dsDNA 的突出端序列杂交。最后，生物素标签依次与链霉亲和素（STV）和生物素转化酶结合。转化酶有效地催化蔗糖水解以产生丰富的葡萄糖，从而导致血糖​​仪的放大响应。该策略可检测低至 0.3 U mL-1 的 DNA MTase 活性，对其他两种胞嘧啶 MTase（HaeIII MTase 和 AluI MTase）具有良好的选择性，并成功应用于筛选 DNA MTase 抑制剂（5-azacytidine 和 5-aza- 2'-脱氧胞苷），