Logic gates based on G-quadruplexes: principles and sensor applications

This review (with 139 refs.) gives a fundamental introduction into the sensors and logic gates based on G-quadruplexes (G4s). G4 characterizes vibrant binding activities and topology diversity, which contribute to the multiple signal output modes (including labeled moieties based on distance changes, label-free outputs by employing fluorescent ligands, G4/hemin DNAzyme with catalyzing activity and colorimetric readout using gold nanoparticles) and versatile design strategies (including target-induced G4 formation/disruption, liberation of blocked G4, split G4 probes, polymerase-assisted amplification and G4/hemin enrichment on sensor surface) of G4s-based methods. Following two important trends in logic gates (application of intelligent detection schemes and logic circuit constructions), specific sections review logic sensors and logic circuits based on G4s with several representative examples. We close this review with conclusions and give a perspective that employment of DNA technologies (such as aptamers, DNA junctions/origami, toehold-mediated strand displacement, enzyme-assisted amplification, metal ion-dependent DNAzymes) and various nanomaterials in G4s-based methods results in quite a large potential in terms of logic detection and construction of logic circuits.