Quantification of DNA through a fluorescence biosensor based on click chemistry.

A simple, sensitive and selective fluorescence biosensor for determination of DNA using CuS particles based on click chemistry is reported. Biotin-modified capture DNA was modified on Streptavidin MagneSphere Paramagnetic Particles (PMPs) and hybridized with target DNA (hepatitis B virus DNA had been chosen as an example), then bound target DNA was hybridized with DNA-CuS particles and formed a sandwich like structure. CuS particles on the sandwich structures can be destroyed by acid to form Cu(II), and Cu(II) can be reduced to Cu(I) by sodium ascorbate, which in turn catalyzes the reaction between a weak-fluorescent 3-azido-7-hydroxycoumarin and propargyl alcohol to form a fluorescent 1,2,3-triazole compound. Using this method, target DNA concentration can be determined by a change in the fluorescence intensity of the system. It is found that the fluorescence increase factor has a direct linear relationship to the logarithm of target DNA concentrations in the range of 0.1 to 100 nM, and the detection limit is 0.04 nM (S/N = 3). The proposed sensor not only allows high sensitivity and good reproducibility, but also has a good selectivity to single-nucleotide mismatches.

Fluorescence sensor for Cu(II) in the serum sample based on click chemistry.

Cu(II) can be reduced to Cu(I) by sodium ascorbate (SA) in situ, which in turn induces CuAAC reaction between the weak fluorescent compound (3-azido-7-hydroxycoumarin) and propargyl alcohol to form a strong fluorescent compound. Based on such principle, a simple and sensitive fluorescence sensor for Cu(II) can be developed, which combines the character of high selectivity of click chemistry and high sensitivity of fluorescence detection. The value of fluorescence increase factor shows a good linear relationship with the concentration of Cu(II) in the range of 0.25 µM-2.5 µM with a detection limit of 0.08 µM. In addition, the developed sensor shows high selectivity towards Cu(II) assay even in the presence of other common metal ions and it has been successfully applied to detect Cu(II) in human serum with satisfactory results.

Novel colorimetric molecular switch based on copper(I)-catalyzed azide-alkyne cycloaddition reaction and its application for flumioxazin detection.

A novel colorimetric switch based on the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction has been developed. G-quadruplex-hemin DNAzyme catalyzes the oxidation of 2,2'-azinobis(3-ethylbenzothiozoline)-6-sulfonic acid (ABTS) to form ABTS˙(+), the UV absorbance of the solution increased greatly and the color of the solution changed to dark green. However, in the presence of an azide complex, the absorbance signal decreased and the solution became light green since the catalytic ability of the hemin was inhibited by the azide groups. However, once propargylamine has been added into the above reaction system, which would react with azide groups through the CuAAC reaction, the solution becomes dark green again and the absorption intensity of the system is also increased. The proposed switch allows a good reversibility and can be identified clearly by the naked eye. In addition, the method has been applied to detect some pesticides, which have alkynyl groups (flumioxazin), with high sensitivity and selectivity, where the UV absorbance has a direct linear relationship with the logarithm of flumioxazin concentrations in the range of 0.14-14 nM, and the limit of detection was 0.056 nM (S/N = 3), which can meet the requirement of the maximum residue limits (MRLs) of United States of America (56 nM).