Another important issue in biosensors is to design a
Another important issue in biosensors is to design a simple and potable detection strategy to meet the requirement of the point-of-care (POC) test applications. According to the recent research, by using invertase NSC228155 for hydrolyzing sucrose into glucose, the range of personal glucometer has been expanded to monitor other biomolecules (protein and DNA biomarkers) beyond glucose (Xiang et al., 2011; Xiang et al., 2012). We have already fabricated a glucometer-based DNA MTases biosensor labeled with invertase (Chen et al., 2018), which sets the stage for the further development. Herein, a dual-response (EC and glucometer) biosensor for DNA MTase activity detection based on functionalized MOFs was reported for the first time. In this study, gold nanoparticles and copper (Cu2+)-MOFs nanocomposites (Au/CuMOFs) acted as not only a well-defined EC redox probe attributing to the coordinated Cu2+ but also an ideal loading platform to immobilize invertase for catalyzing sucrose to glucose, which realized the EC and glucometer responses for DNA MTase detection. The high density of metal sites in MOFs and the plentiful invertase on Au/CuMOFs with high efficiency of catalysis realized signal amplifications. The EC and glucometer signal intensities were proportional to the amount of the DNA MTase. The significance of this work lies in the dual-response for accurate detection of DNA MTase, which can reduce false positive result and benefit early diagnosis and therapeutic applications.
Results and discussion
Conclusion In summary, we developed a facile way to synthesize a biocompatible Au/CuMOF material and explored its application in constructing a dual-response Dam MTase sensor. The present assay brought good performances with detection limit of 0.001 U mL−1 and wide linear range from 0.002 to 12 U mL−1. Such sensitivity was ascribed to the excellent loading capacity of Au/CuMOF providing abundant Cu2+ and invertases as well as the high catalytic efficiency of invertase toward substrates. Moreover, the developed method showed good selectivity and could be potentially applied for inhibitors screening. With these merits, this dual-response, accurate and sensitive assay shows promise for applications in early clinical diagnosis and therapeutic applications.
Acknowledgements This work was financially supported by the National Natural Science Foundation of China (no. 21605007).
Introduction DNA methylation catalyzed by methylase plays an important role in cell proliferation, genomic stability, and senescence in both eukaryotes and prokaryotes , . The process is implemented when DNA methyltransferases (MTases) transfer a methyl group from S-adenosyl-L-methionine (SAM) to cytosine or adenine bases . Aberrant DNA methylation would cause tumor suppressor genes inactivation and transcriptional silencing gene expression . Importantly, changes in DNA MTase activity generally occur long before other marks of cancer . Therefore, the level of methylation is closely associated with DNA MTase activity , , . Recent reports have demonstrated that DNA MTase may become a potential biomarker to clinical diagnostics and therapeutics , , . Highly sensitive, accurate detection of DNA MTase activity would likely lead to equally accurate diagnosis of genetic disease. MTase activity assays based on HPLC , , mess spectrum , , colorimetric methods , , real-time PCR-based methylation-specific PCR , electrogenerated chemiluminescence , and fluorescence methods  have been reported. Although these approaches have made significant contributions to the detection of MTase activity, their application is time-consuming, labor-intensive, complicated and expensive. This calls for developing simple assay for MTase activity with high sensitivity and selectivity. Electrochemical biosensors have attracted substantial attention owing to their simple instrumentation, high sensitivity, and miniaturization , , . These techniques are promising alternative to colorimetric and fluorescence assays in detecting DNA MTase activity . Liu et al. reported an electrochemical assay to detect MTase activity and inhibitor screening based on a ferrocene (Fc) acetic acid-labeled DNA probe coupled with HpaII endonuclease . Still another electrochemical method employs methylene blue (MB)-conjugated DNA as a response probe . The reported electrochemical methods mainly rely on the target response signal from only one DNA strand of the DNA duplex, while the response signal from another DNA strand is not used reasonably. In reality, utility of response signals from electroactive labeled duplex DNA strands can improve the sensitivity and selectivity of electrochemical biosensors. While some studies have reported the multiplexed sensors utilizing two redox species to detect two different analytes , superimposing dual-signal change as an amplification strategy in the detection of DNA MTases has not been reported. Herein, we take advantage of DNA sequences which can be folded into G-quadruplex structures , coupling with hemin and the Fc-labeled DNA as two independent signals to detect DNA MTases with the help of Exo III .