In this study, we present a fluorescent switch-on probe based on a cyanovinyl-pyridinium triphenylamine (CPT) derivative that exhibited a 190-fold increase in fluorescence upon binding to G-quadruplex-forming oligonucleotide 22AG. This probe showed specificity and selectivity towards an antiparallel G-quadruplex, indicating its promising potential in G-quadruplex imaging.

We have presented a fluorescent probe that exhibits a fluorescence turn-on signal upon reaction with tyrosinase, and we show that it can be readily employed for the assessment of tyrosinase activity and tyrosinase inhibitor activities in buffered aqueous solution.

Based on graphene oxide and Hoechst 33258, bioassays towards target DNA and several enzymes including Exo III and Dam MTase were established. This strategy eliminates the need for modification of oligonucleotides, and can give similarly satisfactory results compared to traditional methods using labelled DNA. Moreover, “AND” and “INHIBIT” dual-output DNA logic gates were developed.

Ruthenium complexes are well known for their high affinity and reactivity with DNA. There are so many reports about the interactions of ruthenium complexes and duplex DNA. However, their effects on other DNA structures are poorly studied. In this paper, the photo-activated DNA cleavage by two ruthenium(II) complexes was researched. It was found that these complexes can selectively act on the guanosine bases located in DNA non-duplex portions which were contained in the well matched duplex structures. The mechanism was also studied and considered to be a singlet oxygen oxidation. Through the molecular modeling experiment, we proposed that the strong interaction of complexes with non-duplex DNA structure cause the structural selectivity of DNA cleavage. The research show great future prospects of these ruthenium complexes to be used in anticancer drug development and nucleic acid structure research.Graphical abstractThe ruthenium(II) complexes could selectively cleave the guanosine bases in loop and bulge but have no cleavage reaction in the duplex portion.Highlights► The photo-activated DNA cleavage by two ruthenium(II) complexes was researched. ► The complexes can selectively cleave the G-base which located in the non-duplex region. ► The interaction of complexes with DNA was simulated by the molecular modeling experiments. ► The strong interaction of complexes with non-duplex DNA structure leads the selectivity.

Sensitive and selective techniques for both Ag+ and Cys detection have been designed based on graphene oxide (GO) and G-quadruplex DNA. The G-quadruplex structure can capture the fluorescent molecule acridine orange (AO) from the surface of graphene oxide (GO), which will recover the fluorescence of AO that was initially quenched by GO. Then the addition of Ag+ will release AO back to GO, because Ag+ can destroy the G-quadruplex structure, giving a fluorescence quenching process again. Based on this “turn off” principle, a highly sensitive and selective Ag+ detection method was developed. In addition, cysteine (Cys) can capture Ag+ from the guanine base of DNA which will result in the regeneration of the G-quadruplex DNA structure and thus the regeneration of the fluorescence signal. This “turn on” principle can be used for the development of a highly selective and sensitive detection method for Cys.

Based on graphene oxide and Hoechst 33258, bioassays towards target DNA and several enzymes including Exo III and Dam MTase were established. This strategy eliminates the need for modification of oligonucleotides, and can give similarly satisfactory results compared to traditional methods using labelled DNA. Moreover, “AND” and “INHIBIT” dual-output DNA logic gates were developed.

Sensitive and selective techniques for both Ag+ and Cys detection have been designed based on graphene oxide (GO) and G-quadruplex DNA. The G-quadruplex structure can capture the fluorescent molecule acridine orange (AO) from the surface of graphene oxide (GO), which will recover the fluorescence of AO that was initially quenched by GO. Then the addition of Ag+ will release AO back to GO, because Ag+ can destroy the G-quadruplex structure, giving a fluorescence quenching process again. Based on this “turn off” principle, a highly sensitive and selective Ag+ detection method was developed. In addition, cysteine (Cys) can capture Ag+ from the guanine base of DNA which will result in the regeneration of the G-quadruplex DNA structure and thus the regeneration of the fluorescence signal. This “turn on” principle can be used for the development of a highly selective and sensitive detection method for Cys.