Shijun Shao

A Bodipy-based derivative for selective fluorescence sensing of homocysteine and cysteine

A method for the selective fluorescence sensing of homocysteine (Hcy) and cysteine (Cys) under neutral pH conditions, based on the reaction of the simple aldehyde containing Bodipy dye with Hcy/Cys, has been developed. The location of the aldehyde group at the Bodipy core is important and has an effect on the cyclization with Hcy/Cys.

Fingerprint quality control of Angelica sinensis (Oliv.) Diels by high-performance liquid chromatography coupled with discriminant analysis

High-performance liquid chromatography (HPLC) was employed in the fingerprint analysis of Angelica sinensis (Oliv.) Diels. A chromatographic profile of A. sinensis (Oliv.) Diels from the Dingxi District of Gansu province, China, was established as the characteristic fingerprint. The feasibility and advantages of employing chromatographic fingerprint combined with discriminant analysis were investigated and demonstrated for the evaluation of A. sinensis (Oliv.) Diels for the first time. Our results showed that the chromatographic fingerprint combining with discriminant analysis can efficiently distinguish A. sinensis (Oliv.) Diels from various areas.

A selective chromogenic molecular sensor for acetate anions in a mixed acetonitrile-water medium†

Quinonehydrazone compound , as a new chromogenic anion sensor, can selectively detect AcO(-) over F(-) and other anions in mixed acetonitrile-water media. The deprotonation of the N-H proton of the sensor is responsible for the drastic color change. An acidic C-H group in the receptor, probably acting as an accessorial binding site, is essential to the selectivity and affinity for sensing the acetate anions.

New non-covalent charge–transfer complex of calix[4]pyrrole–chloranil: as a potential colorimetric anion sensor

Non-covalent calix[4]pyrrole–chloranil complex, a new class of supramolecular assembly, is reported. The formation of the complex is mainly attributed to the charge–transfer interactions between calix[4]pyrrole with electron-rich pyrrole rings and the electron-deficient chloranil subunit. As potential colorimetric anion sensors, the charge–transfer aggregation may be used for effective and selective detection of F− and H2PO4− by means of dramatic visual color changes.

Hairpin assembly-triggered cyclic activation of a DNA machine for label-free and ultrasensitive chemiluminescence detection of DNA

DNA plays important regulatory roles in many life activities. Here, we have developed a novel label-free, ultrasensitive and specific chemiluminescence (CL) assay protocol for DNA detection based on hairpin assembly-triggered cyclic activation of a DNA machine. The system involves two hairpin structures, H1 and H2. Firstly, a target DNA binds with and opens the hairpin structure of H1. Then, H2 hybridizes with H1 and displaces the target DNA, which is used to trigger another new hybridization cycle between H1 and H2, leading to the generation of numerous H1-H2 complexes. The generated H1-H2 complexes are further activated with the help of polymerase and nicking enzyme, continuously yielding a large amount of G-riched DNA fragments. The G-riched DNA fragment products interact with hemin to form the activated HRP-mimicking DNAzymes that can catalyze the oxidation of luminol by H2O2 to produce strong CL signal resulting in an amplified sensing process. Our newly proposed homogeneous assay enables the quantitative measurement of p53 DNA (as a model) with a detection limit of 0.85 fM, which is at least 5 orders of magnitude lower than that of traditional unamplified homogeneous optical approaches. Moreover, this assay exhibits high discrimination ability even against a single base mismatch. In addition, this strategy is also capable of detecting p53 DNA in complex biological samples. The proposed sensing approach might hold a great promise for further applications in biomedical research and early clinical diagnosis.

Ultrasensitive electrochemical sensing of the anticancer drug tirapazamine using an ordered mesoporous carbon modified pyrolytic graphite electrode

A new ordered mesoporous carbon (OMC) modified pyrolytic graphite electrode (PGE) was prepared to investigate electrochemical behavior of the anticancer drug tirapazamine (TPZ). Compared to the bare PGE, the modified electrode showed an excellent electrochemical response to TPZ. The anodic peak current (I(pa)) of TPZ at the OMC/PGE is 180-fold higher than that of the bare PGE. The I(pa) is proportional with TPZ concentration in the range of 5.0 x 10(-11) to 1.5 x 10(-5) mol L(-1). The linear regression equations are I(pa) (microA)=0.0000044+16.928C(TPZ) (micromolL(-1)), with a detection limit (S/N=3) of 2.0 x 10(-11) mol L(-1). This proposed method can be potentially used for ultrasensitive electrochemical sensing of TPZ in physiological condition.

A BODIPY-based turn-on fluorescent probe for the selective detection of hydrogen sulfide in solution and in cells.

A new turn-on fluorescent probe, incorporating 7-nitrobenzoxadiazole (NBD) ether group into a BODIPY molecule, was synthesized and studied for the detection of H2S and biothiols in aqueous solution and in living cells. The design was based on thiol-induced thiolysis of the NBD ether bond and followed by the cleavage and the release of free meso-(4-hydroxybenzyl)-substituted BODIPY fluorophore. The BODIPY-based probe displayed highly sensitive and selective fluorescence enhancement respond to H2S over competing biothiols such as cysteine (Cys) and glutathione (GSH), mainly due to the weak reactivity of biothiols toward the probe. There was a good linearity between the fluorescence intensity and the concentrations of H2S in the range of 1-200 µM with a detection limit of 2.6 µM. The proposed reaction mechanism was confirmed by mass spectrometry and optical spectroscopy, and the mechanism of turn-on fluorescent response was further determinated by the density functional theory (DFT) calculations using Gaussian 03 program. Moreover, the probe was successfully applied for the fluorescence imaging of H2S in HeLa cells under physiological conditions (pH 7.4).

A reversible fluorescence probe for detection of ClO−/AA redox cycle in aqueous solution and in living cells

Based on the reversible redox reaction of 4-amino-2,2,6,6-tetramethyl-piperidin-1-ol with oxidative ClO(-) and reductive ascorbic acid (AA), a reversible fluorescent probe, incorporating 4-amino-2,2,6,6-tetramethyl-piperidin-1-ol group into a 7-nitrobenzoxadiazole (NBD) fluorophore, was synthesized and studied for the cyclic detection of ClO(-)/AA in aqueous solution. The NBD-based probe displayed sensitive and selective On-Off-On fluorescent responses to ClO(-)/AA and was successfully applied to monitor the ClO(-)/AA redox cycle in living HeLa cells under physiological conditions.

Selective electrochemical determination of trace level copper using a salicylaldehyde azine/MWCNTs/Nafion modified pyrolytic graphite electrode by the anodic stripping voltammetric method

A novel Cu2+ electrochemical sensor based on a salicylaldehyde azine/MWCNTs/Nafion-modified pyrolytic graphite electrode was prepared for anodic stripping analysis of Cu2+. Salicylaldehyde azine was synthesized and then used for the selective determination of the heavy metal pollutant Cu2+ due to its azine structure, which gave selective complexing ability toward Cu2+. The use of MWCNTs with their strong adsorption ability could greatly enhance the sensitivity. Nafion, a proton-exchange polymer, was used as the conductive matrix in which the salicylaldehyde azine and MWCNTs could be strongly fixed to the substrate electrode surface. The as-prepared electrochemical sensor showed remarkably enhanced selectivity and sensitivity towards Cu2+. The response current of the sensor was linear with Cu2+ concentration ranging from 5 to 300 nM under 15 min accumulation at open-circuit potential, with a very low detection limitation of about 1 nM. The hybrid functionalized electrode also exhibited good selectivity to avoid the interference of other heavy metal ions like Cd2+, Pb2+ and Hg2+ in the mixture solution together with Cu2+. Real application towards environmental sample analysis confirmed that the modified electrode could be applied for the selective determination of trace levels of Cu2+ in the Yellow River.

pH-Responsive chromogenic-sensing molecule based on bis(indolyl)methene for the highly selective recognition of aspartate and glutamate

Summary Bis(indolyl)methene displays high selectivity and sensitivity for aspartate and glutamate in water-containing medium based on the proton transfer signaling mode. The presence of acid can easily induce proton transfer to the basic H-bond acceptor moiety, which modulates the internal charge transfer state of the bis(indolyl)methene skeleton and gives rise to dramatic change in color. The detection limits for aspartate and glutamate were 0.80 ppm and 1.12 ppm, respectively.