Versatile G-quadruplex-mediated strategies in label-free biosensors and logic systems

G-quadruplex (G4), as one of the significant functional nucleic acids (FNAs), has attracted researchers' wide attention, and in particular has been employed for the construction of label-free molecular sensors and logic systems based on the peroxidase-like activity of the G4-hemin complex and G4-enhanced luminescence of G4-binding organic dyes. Its cation-dependent conformation and stability provide opportunities for the recognition of metal ion inputs and application of a split G4 strategy. Moreover, coupling the G4 sequence with other FNAs, e.g. metal ion-dependent DNAzymes and aptamers, has prominently broadened the range of possible targets from metal ions and DNA to diverse proteins and cells. Although there are limitations, such as a low ability of anti-interference and multiplex analysis, the excellent advantages (e.g. simplicity and low cost) endow the G4-mediated strategy with tremendous potential to be further exploited for practical bioanalysis and complicated DNA computing.