Bingyan Han

Sensitive and Selective Sensor for Biothiols in the Cell Based on the Recovered Fluorescence of the CdTe Quantum Dots−Hg(II) System

Herein, a sensitive and selective sensor for biothiols based on the recovered fluorescence of the CdTe quantum dots (QDs)-Hg(II) system is reported. Fluorescence of QDs could be quenched greatly by Hg(II). In the presence of biothiols, such as glutathione (GSH), homocysteine (Hcy), and cysteine (Cys), however, Hg(II) preferred to react with them to form the Hg(II)-S bond because of the strong affinity with the thiols of biothiols rather than quenching the fluorescence of the QDs. Thus, the fluorescence of CdTe QDs was recovered. The restoration ability followed the order GSH > Hcy > Cys due to the decreased steric hindrance effect. A good linear relationship was obtained from 0.6 to 20.0 micromol L(-1) for GSH and from 2.0 to 20.0 micromol L(-1) for Cys, respectively. The detection limits of GSH and Cys were 0.1 and 0.6 micromol L(-1), respectively. In addition, the method showed a high selectivity for Cys among the other 19 amino acids. Furthermore, it succeeded in detecting biothiols in the Hela cell.

Enzyme Colorimetric Assay Using Unmodified Silver Nanoparticles

Colorimetric assay based on the unique surface plasmon resonance properties of metallic nanoparticles has received considerable attention in bioassay due to its simplicity, high sensitivity, and low cost. Most of colorimetric methods previously reported employed gold nanoparticles (GNPs) as sensing elements. In this work, we develop a sensitive, selective, simple, and label-free colorimetric assay using unmodified silver nanoparticle (AgNP) probes to detect enzymatic reactions. Enzymatic reactions concerning adenosine triphosphate (ATP) dephosphorylation by calf intestine alkaline phosphatase (CIAP) and peptide phosphorylation by protein kinase A (PKA) were studied. In the absence of the enzymes, unreacted ATP could protect AgNPs from salt-induced aggregation, whereas in the presence of the enzymes, the reaction product of ATP (i.e., adenosine for CIAP and ADP for PKA) could not. Via our method, dephosphorylation and phosphorylation could be readily detected by the color change of AgNPs, with a detection limit of 1 unit/mL for CIAP and a detection limit of 0.022 unit/mL for PKA. More importantly, the enzymatic inhibition by inhibitors and enzymatic activity in complex biological fluids could also be realized. This work is an important step toward a colorimetric assay using AgNPs and might provide a promise for enzyme assay in realistically complex systems and for screening of different enzyme inhibitors in future.

Oligonucleotide-stabilized fluorescent silver nanoclusters for sensitive detection of biothiols in biological fluids

In this work, we reported a simple and sensitive method to detect biothiols, such as cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), using fluorescent silver nanoclusters (Ag NCs) stabilized by single-stranded DNA (DNA-Ag NCs) as probes. The photoluminescence intensity of DNA-Ag NCs was found to be quenched effectively with the increase of biothiols concentration due to the formed nonfluorescent coordination complex between DNA-Ag NCs and biothiols, resulting in the shift-to-red of emission wavelength. But the fluorescence of DNA-Ag NCs was not changed in the presence of other amino acids at 10-fold higher concentration. Satisfactory detection limits and linear relationships of Cys, GSH and Hcy were obtained, respectively. The resulted plots exhibited good linear relationships in the range from 8.0×10(-9) to 1.0×10(-7) mol L(-1) (R(2)=0.984) for Cys, 8.0×10(-9) to 1.0×10(-7) mol L(-1) (R(2)=0.983) for GSH, and 2.0×10(-6) to 6.0×10(-7) mol L(-1) (R(2)=0.999) for Hcy, respectively; the detection limits of Cys, GSH and Hcy were 4.0 nmol L(-1), 4.0 nmol L(-1), and 0.2 μmol L(-1), respectively. The method was successfully used for the detection of biothiols in human plasma samples.

DNA-templated fluorescent silver nanoclusters

In this review, we discuss the synthesis and applications of DNA-templated fluorescent silver nanoclusters in aqueous solution. Various oligonucleotide sequences or conformations have been utilized to synthesize silver nanoclusters with excellent fluorescence properties. The range of applications has expanded greatly, from live cell staining and the detection of metal ions and small biomolecules to the detection of DNA or proteins.

Sensitive determination of verticine and verticinone in Bulbus Fritillariae by ionic liquid assisted capillary electrophoresis–electrochemiluminescence system

CE/Ru(bpy)(3)(2+) electrochemiluminescence (ECL) system with the assistance of ionic liquids (ILs) was successfully established for sensitive determination of verticine and verticinone in Bulbus Fritillariae for the first time. Migration behavior of alkaloid largely relies on the hydrogen bonding interactions between alkyl imidazolium cations in ILs and the alkaloids. Running buffer containing 40 mmol/L 1-butyl-3-methylimidazolium tetrafluoroborate (BMImBF(4)) IL-8 mmol/L phosphate resulted in significant changes in separation selectivity for alkaloids with similar structures. The highest sensitivity of the detection was obtained by maintaining the detection potential at 1.2V. Under the optimized conditions, relative standard derivations of the ECL intensity and the migration time were 3.27 and 2.84% for verticine and 4.42 and 1.69% for verticinone, respectively. The standard curves were linear between 1x10(-8) and 1x10(-6) mol/L for verticine and between 5x10(-8) and 1x10(-6) mol/L for verticinone, respectively. Detection limits of 1.25x10(-10) mol/L for verticine and 1x10(-10) mol/L for verticinone were obtained (S/N=3). Developed method was successfully applied to determine the amounts of alkaloids in Bulbus Fritillariae.

Surface modification of poly(dimethylsiloxane) microchips using a double-chained cationic surfactant for efficiently resolving fluorescent dye adsorption

This paper described a double-chained cationic surfactant, didodecyldimethylammonium bromide (DDAB), for dynamic surface modification of poly(dimethylsiloxane) (PDMS) microchips to reduce the fluorescent dyes adsorption onto the microchannel. When DDAB with a high concentration was present as the dynamic modification reagent in the running and sample buffer, it not only reversed the direction of electroosmotic flow, but also efficiently suppressed fluorescent dyes pyronine Y (PY) or rhodamine B (RB) adsorption onto the chip surface. In addition, vesicles formed by DDAB in the buffer with higher surface charge density and electrophoretic mobility could provide wider migration window and potential for the separation of compounds with similar hydrophobicity. Factors affecting modification, such as pH and concentrations of the buffer, DDAB concentration in the buffer were investigated. Compared with commonly used single-chained cetyltrimethylammonium bromide, DDAB provided a better modification performance. Furthermore, PY and RB were separated successfully on a PDMS microchip at the appropriate conditions with DDAB.

Determination of arecoline in areca nut based on field amplification in capillary electrophoresis coupled with electrochemiluminescence detection

A sensitive capillary electrophoresis-electrochemiluminescence (CE-ECL) assay with an ionic liquid (IL) was developed for the determination of arecoline in areca nut. The IL, 1-butyl-3-methylimidazolium tetrafluoroborate (BMImBF(4) ), was an effective additive improved not only the separation selectivity but also the detection sensitivity of the analyte. BMImBF(4) in the separation electrolyte made the resistance of the separation buffer much lower than that of the sample solution, which resulted in an enhanced field amplified electrokinetic injection CE. ECL intensity of arecoline is about two times higher than that of the analyte with phosphate-IL buffer system. Resolution between arecoline and other unknown compounds in real samples was improved. Under the optimized conditions (ECL detection at 1.2 V, 16 kV separation voltage, 20 mmol/L phosphate with 10 mmol/L BMImBF(4) buffer at pH 7.50, 5 mmol/L Ru(bpy)(3)(2+) and 50 mmol/L phosphate buffer in the detection reservoir), a detection limit of 5 × 10(-9) mol/L for arecoline was obtained. Relative standard deviations of the ECL intensity and the migration time were 4.51% and 0.72% for arecoline. This method was successfully applied to determination of the amount of arecoline in areca nut within 450 s.

Synthesis of Protein-Directed Orange/Red-Emitting Copper Nanoclusters via Hydroxylamine Hydrochloride Reduction Approach and Their Applications on Hg2+ Sensing

Herein, we report a facile one-pot method for the synthesis of orange/red-emitting fluorescent copper nanoclusters (Cu NCs), in which bovine serum albumin (BSA) served as the capping scaffold (Cu NCs@BSA) and hydroxylamine hydrochloride (NH2OH⋅HCl) as the reducing agent. To the best of our knowledge, this is the first time to adopt this mild reductant to synthesize fluorescent Cu NCs. The as-prepared Cu NCs@BSA exhibits strong orange or red fluorescence at room temperature depending on the synthesis process, and the maximum excitation and emission peaks were at 355nm and 615nm, 395nm and 645nm, respectively. Synthesis conditions including the amounts of NH2OH⋅HCl, the selection of reducing agent, the molar ratio of BSA/Cu(NO3)2, the pH value, the reaction temperature, the reaction time, and various kinds of Cu sources have been systematically studied. Importantly, these Cu NCs exhibit excellent stability for at least 2 months when stored at 4∘C in the dark, and they also show strong oxidation resistance t...