DNA G-quadruplexes are special three-dimensional (3D) DNA nanostructures formed by specific G-rich DNA sequences. These 3D DNA nanostructures can bind with hemin and significantly improve the intrinsic peroxidase activity of hemin. Besides this function, they also enhance the fluorescence intensity of some G-quadruplex-specific dyes. Owing to these features, G-quadruplexes possess several superiorities in the detection of enzymes involved in nucleic acid metabolism, including facile probe fabrication without labeling, simple detection process without washing or separation steps, rapid observation by naked eyes, and easy integration with nucleic acid amplification strategies to amplify signals. Herein, we describe two strategies for label-free detection of enzyme activity based on DNA G-quadruplexes. To increase sensitivity, template-dependent and template-independent DNA amplifications were introduced for the amplification of G-rich DNA sequences. DNA methyltransferase and terminal deoxynucleotidyl transferase were detected as two model analytes, respectively.
Keywords: Colorimetric; DNAzyme; Enzyme activity; G-quadruplex; Label-free; Methyltransferase; Terminal deoxynucleotidyl transferase; Thioflavin T.