Lun Wang

Fabrication of layer-by-layer modified multilayer films containing choline and gold nanoparticles and its sensing application for electrochemical determination of dopamine and uric acid

A novel electrochemical sensor has been constructed by use of a glassy carbon electrode (GCE) coated with a gold nanoparticle/choline (GNP/Ch). Electrochemical impedance spectroscopy (EIS), field emission scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the properties of this modified electrode. It was demonstrated that choline was covalently bounded on the surface of glassy carbon electrode, and deposited gold nanoparticles with average size of about 100nm uniformly distributed on the surface of Ch. Moreover, the modified electrode exhibits strong electrochemical catalytic activity toward the oxidation of dopamine (DA), ascorbic acid (AA) and uric acid (UA) with obviously reduction of overpotentials. For the ternary mixture containing DA, AA and UA, these three compounds can be well separated from each other, allowing simultaneously determination of DA and UA under coexistence of AA. The proposed method can be applied to detect DA and UA in real samples with satisfactory results.

High adsorptive γ-AlOOH(boehmite)@SiO2/Fe3O4 porous magnetic microspheres for detection of toxic metal ions in drinking water

γ-AlOOH(boehmite)@SiO(2)/Fe(3)O(4) porous magnetic microspheres with high adsorption capacity toward heavy metal ions were found to be useful for the simultaneous and selective electrochemical detection of five metal ions, such as ultratrace zinc(II), cadmium(II), lead(II), copper(II), and mercury(II), in drinking water.

A flow injection chemiluminescence method for the determination of fluoroquinolone derivative using the reaction of luminol and hydrogen peroxide catalyzed by gold nanoparticles

Based on the enhancement of chemiluminescence (CL) of luminol-hydrogen peroxide-gold nanoparticles system by fluoroquinolones (FQs), a novel and rapid CL method is reported for the determination of FQs derivatives. Under the optimum conditions, the CL intensity is proportional to the concentration of FQs derivative in solution. The corresponding linear regression equations are established over the range of 0.08-1.28mug/mL for norfloxacin, 0.013-1.32mug/mL for ciprofloxacin, 0.014-1.4mug/mL for lomefloxacin, 0.029-1.46mug/mL for fleroxacin, 0.02-1.0mug/mL for ofloxacin and 0.01-1.44mug/mL for levofloxacin, respectively. The limits of detection (S/N=3) are 3.2, 9.5, 7.0, 9.0, 8.0, and 8.0ng/mL with the relative standard deviation (n=11) 4.3, 1.5, 1.9, 1.3, 1.6 and 2.1% for norfloxacin, ciprofloxacin, lomefloxacin, fleroxacin, ofloxacin and levofloxacin, respectively. This proposed method has been applied to detect FQs derivatives in human urine successfully.

Fluorescent blood glucose monitor by hemin-functionalized graphene quantum dots based sensing system

In the present work, a highly sensitive and specific fluorescent biosensor for blood glucose monitoring is developed based on hemin-functionalized graphene quantum dots (GQDs) and glucose oxidase (GOx) system. The GQDs which are simply prepared by pyrolyzing citric acid exhibit strong fluorescence and good water-solubility. Due to the noncovalent assembly between hemin and GQDs, the addition of hemin can make hydrogen peroxide (H2O2) to destroy the passivated surface of GQDs, leading to significant fluorescence quenching of GQDs. Based on this effect, a novel fluorescent platform is proposed for the sensing of glucose. Under the optimized conditions, the linear range of glucose is from 9 to 300μM, and the limit of detection is 0.1μM. As unique properties of GQDs, the proposed biosensor is green, simple, cost-efficient, and it is successfully applied to the determination of glucose in human serum. In addition, the proposed method provides a new pathway to further design the biosensors based on the assembly of GQDs with hemin for detection of biomolecules.

Application of functionalized CdS nanoparticles as fluorescence probe in the determination of nucleic acids.

Nanometer-sized fluorescent particles were successfully synthesized. The nanoparticles have a narrow, tunable, symmetric emission spectrum and a broad, continuous excitation spectrum. They are also photochemically stable. A synchronous fluorescence method was developed for the rapid determination of DNA with functionalized CdS as a fluorescence probe, based on the synchronous fluorescence quenching of functionalized CdS in the presence of DNA. Maximum fluorescence is produced at pH 7.0, with maximum excitation and emission wavelengths of 360 and 620 nm, respectively. The maximum emission wavelength of synchronous fluorescence is 354 nm when delta lambda = 260 nm. Under optimum conditions, the calibration graphs are linear over the range 0-3.5 microg mL(-1) for calf thymus DNA (CT-DNA) and 0.2-3.0 microg mL(-1) for fish sperm DNA. The corresponding detection limit is 0.01 microg mL(-1) for CT-DNA and 0.02 microg mL(-1) for fish sperm DNA. The relative standard deviation of seven replicate measurements is 2.2% for 1 microg mL(-1) calf thymus DNA and 2.4% for 1 microg mL(-1) fish sperm DNA. The method is simple, rapid and sensitive. The recovery and relative standard deviation are very satisfactory.

Hydrogen peroxide sensing using ultrathin platinum-coated gold nanoparticles with core@shell structure.

Ultrathin platinum-coated gold (Pt@Au) nanoparticles with core@shell structure have been developed by under-potential deposition (UPD) redox replacement technique. A single UPD Cu replacement with Pt(2+) produced a uniform Pt monolayer on the surface of gold nanoparticles, which are immobilized on glassy carbon electrode (GCE) surface based on electrostatic interaction. The ultrathin Pt@Au nanoparticles were confirmed by cyclic voltammetry and X-ray photoelectron spectroscopy (XPS). Voltammetry and amperometric methodologies were used to evaluate the electrocatalytic activity of the Pt@Au nanoparticles modified electrode towards the reduction of hydrogen peroxide under the physiological condition. The present results show that ultrathin Pt coating greatly enhances the electrocatalytic activity towards the reduction of hydrogen peroxide, which can be utilized to fabricate the hydrogen peroxide sensor. Chronoamperometric experiments showed that at an applied potential of 0.08 V (vs. Ag/AgCl), the current reduction of hydrogen peroxide was linear to its concentration in the range of 1-450 μΜ, and the detection limit was found to be 0.18 μM (signal-to-noise ratio, S/N=3).

Aptamer-based sensing for thrombin in red region via fluorescence resonant energy transfer between NaYF4:Yb,Er upconversion nanoparticles and gold nanorods

In this work, we design a FRET system for sensitive and selective determination of thrombin in red region, in which NaYF₄:Yb,Er upconversion nanoparticles (UCNPs) act as donor and gold nanorods (Au NRs) act as acceptor. NaYF₄:Yb,Er UCNPs with a strong emission at 661 nm were successfully synthesized by tuning the doped ions ratio. Carboxyl-functionalized NaYF₄:Yb,Er UCNPs and Au NRs were then prepared and conjugated with the thrombin aptamers, respectively. The fluorescence emission band of NaYF₄:Yb,Er UCNPs (λ(max)=661 nm) highly overlaps with the absorption band of Au NRs(λ(max)=666 nm), which benefits from the large tunability of the spectrum band of Au NRs. A FRET system was then formed when thrombin was added to the mixture of NaYF₄:Yb,Er UCNPs and Au NRs, which were both modified thrombin aptamers. The fluorescence quenching efficiency of NaYF₄:Yb,Er UCNPs was increased in a thrombin concentration-dependent manner, which built the principle of thrombin quantification. The linear range was 2.5-90 nM in an aqueous buffer, and 3.75-112.5 nM in spiked human serum samples for thrombin. It also demonstrates a high selectivity to other biological species due to the specific binding. The measurement of thrombin in human plasma is satisfying, suggesting that the FRET system is of practical value in a complex biological sample matrix in red region.

Fluorescence for the determination of protein with functionalized nano-ZnS

ZnS nanoparticles have been prepared and modified with sodium thioglycolate. The functionalized nanoparticles are water-soluble. They were used as fluorescence probes in the determination of proteins, which was proved to be a simple, rapid and specific method. In comparison with single organic fluorophores, these nanoparticle probes are brighter, more stable against photobleaching, and do not suffer from blinking. Under optimum conditions, linear relationships were found between the enhanced intensity of fluorescence at 441 nm and the concentration of protein in the range 0.1-4.0 microg mL(-1) for human serum albumin (HSA), 0.2-3.0 microg mL(-1) for bovine serum albumin (BSA) and 0.1-4.5 microg mL(-1) for gamma-globulin (gamma-G). The limits of detection were 0.015 microg mL(-1) for HSA, 0.024 microg mL(-1) and 0.017 microg mL(-1) for BSA and gamma-G, respectively. The method has been applied to the analysis of human serum samples collected from the hospital and the results were in good agreement with those reported by a hospital, indicating that the method presented here is not only sensitive and simple, but also reliable and suitable for practical application.

A novel nonenzymatic fluorescent sensor for glucose based on silica nanoparticles doped with europium coordination compound

Amino-functionalized luminescent silica nanoparticles (LSNPs) doped with the europium(III) mixed complex, Eu(TTA)(3)phen with 2-thenoyltrifluoroacetone (TTA) and 1,10-phenanthroline(phen) were synthesized successfully using an revised Stöber method. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared (FTIR), and fluorescence spectroscopy were performed for characterizing the synthesized nanoparticles. In the presence of glucose, the fluorescence intensity of the amino-functionalized LSNPs was enhanced due to the enhanced fluorescence resonance energy transfer. Based on fluorescence-enhancing effect, a simple and sensitive method for the determination of glucose was proposed. Under the optimized experimental conditions, the enhanced fluorescence intensity ratio (DeltaF/F(0)) was linear with the concentration of glucose (c) in the range of 0.0-180 microg ml(-1) with a detection limit of 0.8 microg ml(-1) (S/N=3). The R.S.D. values were 0.33% and 0.37% at the levels of 22.5 and 100 microg ml(-1), respectively. The proposed method was applied to the determination of glucose in synthetic samples with satisfactory results. The proposed method was also performed to the analysis of blood glucose in human serum samples and the results were in good agreement with clinical data provided by the hospital, which indicates that the method presented here is not only simple, sensitive, but also reliable and suitable for practical applications.

CdS nanocrystal induced chemiluminescence: reaction mechanism and applications

Water-soluble CdS nanocrystals (NCs) capped with mercaptoacetic acid (MA) were synthesized in aqueous solution. Hydrogen peroxide directly oxidized the MA-capped CdS NCs and produced strong chemiluminescence (CL) emission in basic conditions. It was found that the CL of CdS NCs was size-dependent, and the CL intensity increased with increasing CdS NCs size. UV–visible spectra, CL spectra, photoluminescence (PL) spectra, and transmission electron microscopy (TEM) were used to investigate the CL reaction mechanism. Moreover, the effects of reactant concentrations, surfactants, and some biological molecules and metal ions were carefully investigated. Some biological molecules and metal ions were observed to inhibit the CL signal of the H2O2–CdS NCs system, which makes it applicable for the detection of such species.