The authors describe a silver(I) mediated fluorescent assay for glutathione (GSH). An allosteric oligonucleotide strand containing a G-rich sequence is used to produce a G-quadruplex, and N-methylmesoporphyrin IX (NMM) is chosen as the fluorescent probe. In the absence of Ag(I), the DNA strand is partially intramolecularly hybridized to form a hairpin structure wherein the G-rich sequence is partially caged. On addition of Ag(I), the hairpin is disrupted by forming C-Ag(I)-C base pairs. As a result, the G-rich sequence is released and folds into a G-quadruplex structure, which is able to bind NMM to generate strong fluorescence at 612 nm. However, in the presence of GSH, due to the strong binding ability between GSH and Ag(I), the C-Ag(I)-C structure is not formed. Hence, the DNA probe reverts back to its original structure and fluorescence is not increased. Based on these findings, a method was worked out that has a detection limit as low as 3.5 nM. Due to the inherent selectivity of the interaction between GSH and Ag(I), the method is highly selective over common potential interfering species. It was successfully applied to the fluorometric determination of GSH in cell extracts.

•The MIP/PSS-rGO/GCE was prepared by electropolymerization of o-PD and daidzein.•The MIP/PSS-rGO/GCE showed high selectivity of daidzein compared with other analogues.•The sensor was successfully applied for determination of daidzein in serum sample.A high sensitive and selective electrochemical sensor for detection of daidzein based on molecular imprinted polymer (MIP) modified electrode was established. The sensitive layer was prepared by electropolymerization of o-phenylenediamine (o-PD) on the surface of Poly (sodium 4-styrenesulfonate)-reduced graphene oxide (PSS-rGO) modified glassy carbon electrode (PSS-rGO/GCE) in the presence of daidzein as a template molecule. The negatively charged poly(sodium 4-styrenesulfonate) units and benzene rings of PSS-rGO can attract positive charged o-PD and provide π-π stacking effect of o-PD and daidzein, which makes the compact imprinted film and more imprinted points. The MIP/PSS-rGO composite could specifically recognize daidzein in aqueous solutions which result in the decrease of peak current of K3[Fe(CN)6]/K4[Fe(CN)6] at the MIP/PSS-rGO/GCE. Under the optimized conditions, the decrease of the peak current was linear with the concentration of daidzein in the range of 1.0-20.0 nM. The detection limit was calculated as 0.5 nM (S/N = 3). Relative to the other structurally similar substances, the current response of the MIP/PSS-rGO/GCE toward daidzein was about 6.0, 3.1, 6.9 and 5.2 times higher than those of puerarin, quercetin, genistein and chrysin which suggesting the high selectivity of MIP/PSS-rGO/GCE. The modified electrode was successfully applied to determine daidzein in human serum and pueraria extraction with satisfied recovery suggesting the potential applications in the daidzein determination of clinical samples and nature products.

In this work, an aptamer-based fluorescent strategy for label-free detection of ATP was developed by using Thioflavin T (ThT) as a fluorescence indicator, which can specifically bind with G-quadruplex DNAs to generate enhanced fluorescence intensity. In the absence of ATP, the folded structure of ATP aptamer allows the intercalation of ThT to produce strong fluorescence signal. However, upon ATP binding to the aptamer where ThT intercalated, the conformational change or distortion of the aptamer is large enough to cause much less intercalation of ThT and consequently drastic suppression of the fluorescence intensity. As such, the concentration of ATP could be identified very easily by observing fluorescence changes of this sensing system. This label-free assay could be accomplished very easily and quickly with a “mix-and-detect” detection method and exhibits high sensitivity to ATP with a detection limit of 33 nM in a wide range of 0.1–1000 μM. Furthermore, this proposed method is capable of detecting ATP in human serum and cell extracts. This method offers several advantages such as simplicity, rapidity, low cost, good stability and excellent selectivity, which make it hold great potential for the detection of ATP in bioanalytical and biological studies.

A novel, sensitive, and rapid method was developed for the determination of pazufloxacin mesylas (PM) by capillary electrophoresis with electrochemiluminescence detection (CE-ECL). It was based on the phenomenon that in base medium, PM enhanced the ECL intensity of tris (2,2′-bipyridyl) ruthenium (II). The influence of several experiment factors such as the detection potential, the concentration of tris (2,2′-bipyridyl) ruthenium (II), the concentration and the pH of phosphate buffer, the electro-kinetic voltage, the injection time, and the separation voltage on the determination of PM was explored in detail. Under the optimized conditions, the detection of PM could be accomplished within three minutes. The enhanced ECL intensity was linear with PM concentration in the range of 0.02−10 mg l−1 (r = 0.9968) with detection limit (S/N = 3) of 4.0 μg l−1. The relative standard deviations (RSD) of ECL intensity and the migration time for eleven continuous injections of 2.0 mg l−1 PM were 4.28% and 1.89%, respectively. This method was successfully applied to PM assay in real samples including injection and human urine. An elementary mechanism was proposed to explain this phenomenon.