Qin Hu

Determination of melamine in powdered milk by molecularly imprinted stir bar sorptive extraction coupled with HPLC.

A novel molecularly imprinted stir bar (MIP-SB) was developed with melamine (MA) as the template molecule in this study. The sorptive capacity of MIP-SB was nearly three times over that of non-imprinted stir bar (NIP-SB). The MIP-SB presented much better selectivity than NIP-SB when used to absorb MA and its analogues. An analytical method to determine MA in powdered milk was established by combining MIP-SB sorptive extraction with HPLC. The liner range was 0.0631-12.6ng/mL with good correlation coefficient of 0.9983, and the limit of detection was 0.0127ng/mL based on three times ratio of signal to noise. This method was successfully applied to the determination of MA in powdered milk with satisfactory results. The method built is simple and suitable for the determination of MA in milk products which is of great significance for quality control of milk products.

Preparation of a stir bar coated with molecularly imprinted polymer and its application in analysis of dopamine in urine.

A molecularly imprinted polymer coated stir bar (MIP-SB) using dopamine as a template was fabricated. The adsorptive capacity of the MIP-SB was almost 4 times over that of non-imprinted stir bar. The MIP-SB showed good extracting selectivity for dopamine when used to adsorb dopamine and its analogs. An analytical method to determine dopamine in urine sample was established by combining MIP-SB sorptive extraction with HPLC-fluorescence detector. The linear range of dopamine concentration was 0.378-18.9ng/ml with correlation coefficient of 0.9990, and the limit of quantification was about 0.0945ng/ml (S/N=10). The recoveries of dopamine with spiked urine samples at three different levels were between 92.3 and 106.9%, and the relative standard deviations were within 13.2% (n=3). The method is simple and suitable for the determination of dopamine in human urine for clinical application.

Determination of dissociation constants of anthrocycline by capillary zone electrophoresis with amperometric detection.

Although daunorubicin, pharmorubicin and idarubicin are important drugs in medical and in pharmaceutical research, the dissociation constants (K(a)) of these substances are frequently not known. A method based on a non-linear model enabling the efficient determination of the K(a) of the three drugs by capillary zone electrophoresis with amperometric detection (CZE-AD) has been demonstrated. The pK(a) values obtained through the method were in agreement with the values by typical spectrophotometric method.

Detection of CEA in human serum using surface-enhanced Raman spectroscopy coupled with antibody-modified Au and γ-Fe₂O₃@Au nanoparticles.

In this present work, a rapid and simple method to detect carcinoembryonic antigen (CEA) was developed by using surface-enhanced Raman spectroscopy (SERS) coupled with antibody-modified Au and γ-Fe2O3@Au nanoparticles. First, Au@Raman reporter and γ-Fe2O3@Au were prepared, and then modified with CEA antibody. When CEA was present, the immuno-Au@Raman reporter and immuno-γ-Fe2O3@Au formed a complex through antibody-antigen-antibody interaction. The selective and sensitive detection of CEA could be achieved by SERS after magnetic separation. Under the optimal conditions, a linear relationship was observed between the Raman peak intensity and the concentration of CEA in the range of 1-50 ng mL(-1) with an excellent correlation coefficient of 0.9942. The limit of detection based on two times ratio of signal to noise was 0.1 ng/mL. The recoveries of CEA standard solution spiked with human serum samples were in the range of 88.5-105.9% with the relative standard deviations less than 17.4%. The method built was applied to the detection of CEA in human serum, and the relative deviations of the analysis results between the present method and electrochemiluminescence immunoassay were all less than 16.6%. The proposed method is practical and has a potential for clinic test of CEA.

Determination of sugars in Chinese traditional drugs by CE with amperometric detection.

A simple, fast and reliable method, based on capillary zone electrophoresis with amperometric detection, for the separation and determination of sucrose, glucose, and fructose in Chinese traditional drugs, namely Astragalus Membranceus (Fish.) Bge, Angelica and Codonopsis pilosula (Franch.) Nannf. was described in this paper. A copper disk electrode was used as working electrode. The optimal conditions of separation and detection were 0.05 mol/l sodium hydroxide buffer (pH 12.7), 5 kV for the separation voltage and +0.65 V (vs. Ag/AgCl) for the detection potential. The linear ranges were from 5.0x10(-6) to 5.0x10(-4) mol/l for all three sugars. The all regression coefficients were more than 0.999. The detection limits were 1.0x10(-6) mol/l for glucose and fructose, and 4.0x10(-6) mol/l for sucrose. The method built in this paper was directly applied to the separation and determination of the three sugars in three Chinese traditional drugs without prior derivatization, and the content for every sugar in the drugs was first assayed. The assay results were satisfactory.

A Ratiometric Fluorescence Universal Platform Based on N, Cu Codoped Carbon Dots to Detect Metabolites Participating in H2O2-Generation Reactions

In this work, a new kind of N, Cu codoped carbon dots (N/Cu-CDs) was prepared via a facile one-pot hydrothermal method by using citric acid monohydrate, copper acetate monohydrate and diethylenetriamine. The prepared N/Cu-CDs with a high quantum yield (50.1%) showed excitation-independent emission at 460 nm. The structure and fluorescence properties of N/Cu-CDs were characterized by high-resolution transmission electron microscopy, fluorescence spectrofluorometer, FT-IR spectrometer, UV-visible spectrophotometer and X-ray photoelectron spectroscopy. N/Cu-CDs were applied to establishing a ratiometric fluorescence probe toward H2O2 based on the inner filter effect (IFE) between N/Cu-CDs and DAP (2,3-diaminophenazine, the oxidative product of o-phenylenediamine (OPD)), and provided a ratiometric fluorescence universal platform for detection of the metabolites participating in H2O2-generation reactions (cholesterol and xanthine). The proposed method was demonstrated to be ultrasensitive and highly selective for cholesterol and xanthine assay with detection limits of 0.03 and 0.10 μM, respectively. The fluorescence probe built was applied to the determination of cholesterol and xanthine in human serum with satisfactory results.

Highly sensitive and selective aptasensor for detection of adenosine based on fluorescence resonance energy transfer from carbon dots to nano-graphite

In this article, a novel aptasensor was fabricated by modifying carbon dots (CDs) with adenosine aptamer (CDs-aptamer) for sensitive, selective and quantitative detection of adenosine (AD). When nano-graphite (NG) as an energy acceptor was added into the CDs-aptamer (energy donor) solution, the fluorescence of CDs-aptamer was quenched due to fluorescence resonance energy transfer (FRET). When AD was present in the solution of CDs-aptamer/NG, the process of FRET was inhibited because of the specific combination between AD and AD aptamer. As a result, the fluorescence of CDs-aptamer was restored due to the dissociation of CDs-aptamer from NG and its change was proportional to the AD concentration. Under the optimized conditions, a linear range was found to be 2-50nM for the detection of AD with a detection limit of 0.63nM. Furthermore, the application of the proposed approach was demonstrated in real sample with satisfying results and it showed promise in diagnostic purpose.

Manganese modified CdTe/CdS quantum dots as an immunoassay biosensor for the detection of Golgi protein-73

In this paper, a new fluorescence bioassay for Golgi protein-73 (GP73), a promising marker for monitoring liver tumor, was developed by using anti-GP73 antibody (GP73 Ab) capped quantum dots (QDs) coupled with protein A/G agarose beads in an attempt to improve the analysis time, cost and operation. First, carboxylic-functionalized Mn modified CdTe/CdS QDs were synthesized and covalently conjugated with GP73 Ab, then protein A/G agarose beads were specifically combined with the QDs-conjugated Ab to form the QDs-Ab-beads conjugate, which could capture and separate GP73 from the sample through simple centrifugation. It was found that the fluorescence intensity of the above QDs-Ab-beads biosensor could be specifically quenched by GP73 added. A simple, rapid and specific quantitative method for GP73 protein was proposed using the as-prepared QDs-Ab-beads as a biosensor. Under the optimized conditions, the calibration curve of the proposed assay showed good linearity with a correlation coefficient of 0.9935 in the concentration range of 20-150 ng/mL of GP73 protein. The limit of detection (defined as 3σ/K) was 10 ng/mL. The method built exhibited a great potential in the clinic test of GP73.

A novel Fe3O4/CdTe fluorescence probe for sialic acid detection based on a phenylboronic acid–sialic acid recognition system

A novel fluorescence method was established for detecting sialic acid (SA) by using phenylboronic acid (PBA)-functionalized Fe3O4/CdTe magnetic nanoparticles as fluorescence probe. Initially, Fe3O4 nanoparticles were modified with amino groups, and then 3-mercapto propionic acid-stabilized CdTe quantum dots (QDs) were covalently linked to the amino-modified Fe3O4 nanoparticles to form Fe3O4/CdTe magnetic fluorescence nanoparticles. Finally, PBA was introduced on the surface of Fe3O4/CdTe to form PBA-functionalized Fe3O4/CdTe magnetic fluorescence nanoparticles. This kind of nanoparticle can specifically recognize SA and its fluorescence intensity is quenched by SA. In addition, the conjugate of the nanoparticles and SA is easy to separate from the sample matrix due to its magnetic properties. Therefore, this nanoparticle can be used as a fluorescence probe to detect SA. Under optimal conditions, the fluorescence intensity of the nano probe was found to be inversely linear with the concentration of SA in a wide range of 50 μg ml−1–1.50 mg ml−1, and the limit of detection was 16 μg ml−1. The PBA-functionalized Fe3O4/CdTe nano probe was applied to the determination of SA in infant formula, and the result showed high accuracy and precision. The PBA-functionalized Fe3O4/CdTe nano probe has the potential to be used to monitor SA in food.

A dual-emissive fluorescent sensor fabricated by encapsulating quantum dots and carbon dots into metal–organic frameworks for the ratiometric detection of Cu2+ in tap water

A novel ratiometric fluorescent (RF) sensor was synthesized via a facile one-pot route by encapsulating quantum dots (QDs) and carbon dots (CDs) having good fluorescence properties into a zeolitic imidazolate framework (ZIF-8, one of the classical metal–organic frameworks). The as-synthesized QDs/CDs@ZIF-8 composite not only possessed the advantages of a RF sensor, but also accumulated target analytes strongly due to the adsorption ability of MOFs. The composite showed good stability and dispersibility in aqueous solution and was further applied to the detection of Cu2+ ions. The QDs/CDs@ZIF-8 composite that is used as a RF sensor exhibited excellent sensitivity and selectivity toward Cu2+. The linear range was 5–100 nM and the LOD was 1.53 nM (3σ/K). The QDs/CDs@ZIF-8 composite could be simply used for detecting Cu2+ in tap water.