G-quadruplex based probes for visual detection and sensing.

Recent advances in colorimetric biosensing have led to rapid methods for target detection, potentially leading to applications on-site, at the point-of-need. This review focuses on one such platform, the G-quadruplex-hemin based DNAzymes, which exhibit peroxidase- like activity. Since their discovery in the late 1990s, various approaches have been adopted in applying the unique catalytic properties of these DNAzymes to detecting nucleic acids, proteins, metal ions and other ligands, through the oxidation of substrate pre-cursors into colored products. G-quadruplex based DNAzymes act as modular units of G-rich DNA sequences, and hence can be synthesized cheaply and conveniently using routine oligonucleotide synthesis. Herein, we discuss the various strategies that have been developed to exploit this class of DNAzymes as candidate probes for optical detection and sensing, for a variety of chemical and biological targets.