Guanhong Xu

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.

Citrate-capped Mn-modified CdSe/CdS quantum dots as luminescent probes for levodopa detection in aqueous solution.

A novel kind of citrate capped Mn-modified CdSe/CdS quantum dots (QDs) was developed. The Mn-modified CdSe/CdS QDs had a narrow, symmetric emission and strong fluorescence with quantum yield over 41%. The interaction between the QDs and levodopa was investigated. The results showed that levodopa selectively quenched the fluorescence intensity of the QDs. Based on the fluorescence quenching of the synthesized QDs by levodopa, a simple, rapid and specific quantitative method for levodopa was proposed. The factors affecting the fluorescence detection for levodopa were studied. Under the optimum conditions, the quenched intensity of the fluorescence versus levodopa concentration from 1 to 100 μM gave a linear response with an excellent correlation coefficient of 0.9996, and the limit of detection (3σ/K) was 2 × 10(-7)M. The contents of levodopa in pharmaceutical tablets were determined by the proposed method and the results agreed with the claimed values.

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.

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.

Manganese modified CdTe/CdS quantum dots as a highly selective probe to detect trace copper element in beer samples

This paper describes the investigation of manganese modified CdTe/CdS quantum dots as a fluorescence probe for trace copper detection. Manganese modified CdTe/CdS quantum dots were prepared in aqueous solution and were characterized by ultraviolet-visible absorbance, fluorescence spectra, transmission electron microscopy and X-ray diffraction. The as-synthesized manganese modified CdTe/CdS QDs presented a high photoluminescence quantum yield of 84%. The functionalized nanoparticles were used as a fluorescence probe for Cu2+. The interference study demonstrated that the normal foreign ions, such as Na+, Mg2+, Al3+et al., had very low interference for the detection of Cu2+, and the calibration plot of F0/F versus concentration of Cu2+ was linear in the range of 5.0 × 10−9 to 5.0 × 10−7 mol L−1 with a correlation coefficient of 0.9991. The ultrasensitive fluorescence probe built was directly applied to the detection of trace copper element in beer samples with satisfactory results.

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.

Preparation and application of imprinted polymer for tetrabromobisphenol A using tetrachlorobisphenol A as the dummy template

In this paper, dummy molecularly imprinted polymer (DMIP) for tetrabromobisphenol A (TBBPA) was prepared with a sol–gel process on the surface of micro-nano silica particles. Tetrachlorobisphenol A was chosen as the dummy template to avoid TBBPA bleeding. The adsorption characteristics of the DMIP for TBBPA were investigated. The DMIP for TBBPA had a large adsorption capacity (230 μmol g−1), which was about 6 times as much as that of the non-imprinted polymer, fast binging kinetics (20 min) and high selectivity for TBBPA. A method for the determination of trace TBBPA in environmental water samples was established by high performance liquid chromatography coupled with solid phase extraction using the DMIP as sorbent. Under the built method, the linear range of TBBPA standard aqueous solution was 0.2–8.0 ng mL−1 with a correlation coefficient of 0.9947 and the limit of detection was 0.1 ng mL−1. The recoveries at 1.0 ng mL−1 of TBBPA spiked with water samples were in the range of 91–93% and the relative standard deviations were all less than 9.0% (n = 5). The results showed that the properties of the DMIP were superior and could be used to separate and enrich trace TBBPA in environment water samples.

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.