Double-stranded DNA nanobridge enhanced fluorescence of crystal violet/G-quadruplex complex for detection of lead ions and crystal violet

• The dsDNA nanobridge illuminates the fluorescence of the CV/G-quadruplex complex. • No molecular markers and expensive porphyrin fluorescent molecules were used. • Only three DNA single strands are used to realize the detection of two pollutants. • This platform has good selectivity and applicability, and builds a logical AND gate. DNAzyme and G-quadruplex are purposed as universal recognition elements to achieve multi-functional signal amplification and readout, showing great potential in the design of biosensors and nanodevices. Herein, the single-stranded DNA (ssDNA) opens the dumbbell-shaped hairpin probes, the generated double-stranded DNA (dsDNA) is constructed as a nanobridge, and the released G-rich sequence is folded into a G-quadruplex village. The fluorescence of crystal violet/G-quadruplex complex villages is enhanced by the dsDNA nanobridge connections. Under the excitation wavelength of 580 nm, the fluorescence emission intensity at 624 nm exhibits a good linearity with the concentration of crystal violet (CV) in the range of 10–250 nM, which can be used for sensitive detection of CV. Additionally, combined with Pb 2+ -dependent DNAzyme, a platform for quantitative detection of Pb 2+ is established. In the concentration range of 5 nM – 25 μM, the fluorescence signal increases with the increase of Pb 2+ concentration. The quantitative detection limit of Pb 2+ by this method is 5 nM, and it possesses good selectivity and recovery for Pb 2+ in a variety of water samples. More importantly, the platform can sensitively detect various metal ions by changing the DNAzyme sequence. It has potential application in the field of environmental monitoring.