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Rapid and highly sensitive detection of tumor marker (TM) is critical for the early diagnosis and treatment of cancers. Herein, utilizing highly bright and water-stable CsPbBr 3 perovskite nanocrystals (NCs) capped with amphiphilic polymer ligand of octylamine-modified polyacrylic acid (OPA) and gold nanoparticles (AuNPs) as reporters, a lateral flow immunoassay (LFIA) strip is developed for fluorescence and colorimetric dual-mode detection of carcinoembryonic antigen (CEA). The prepared CsPbBr 3 NCs capped by an amphiphilic polymeric of OPA ligand showed high stability and bright fluorescence. Moreover, the AuNPs immunoprobes were captured with CEA antigen and quench the green fluorescence of CsPbBr 3 /OPA NCs on the T line due to the inner filter effect (IFE). Therefore, CEA could be quantitative analyzed by the dual-readout of fluorescence and colorimetric signal. The detection limits of CEA can reach as low as 0.023 ng/mL and 0.027 ng/mL for the fluorescence and colorimetric mode, respectively. Good specificity and reproducibility were also demonstrated for this method. Finally, the CsPbBr3/OPA NCs-based LFIA showed good accuracy in detection of CEA level from clinical serum samples. This work firstly enables the application of CsPbBr 3 perovskite NCs in a LFIA, displaying great potential in point-of-care clinical diagnosis., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Non-invasive wearable sweat glucose sensors are expected to be highly desirable for personalized diabetes management. Therefore, developing facile, convenient, and scalable manufacturing method of such wearable sensors is urgently needed. Herein, we report a simple and low-cost stamping-vacuum filtration dry transfer (SVFDT) method for construction of a wearable sweat glucose electrochemical sensor. In this patch, a three-electrode array template was made by using a polyvinyl chloride (PVC) stamp, followed by the preparation of multiwalled carbon nanotubes (MWCNTs)/polydimethylsiloxane (PDMS) (MP) film electrode using the vacuum-filtration dry transfer method. In addition, for further enhancing the conductivity of the electrode, another similar stamp with a raised surface dipping carbon nanotubes (CNTs) conductive coating was stamped on the surface of the MP electrode to obtain CNTs/MWCNTs/PDMS (CMP) electrode. CMP electrode was modified with the enzyme-like Ni-Co metal-organic framework (MOF) material which showed good electro-catalytic activity and achieved high sensitivity for glucose detection with a low detection limit of 6.78 μM and a wide linear range of 20 μM - 1.1 mM. More importantly, the Ni-Co MOF modified CMP (NCMP) electrode also displayed high stability under stretching and bending conditions. Finally, the sweat absorbent cloth was combined with the NCMP film electrode to form a wearable flexible electrochemical sensor patch, which could adhere to the skin to enrich sweat and realize real-time detection of sweat glucose with high accuracy. This SVFDT method can also be applied to the fabrication of other electronic devices., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Monitoring cortisol, a hormone released by the adrenal cortex in response to stress, is essential to evaluate the endocrine response to stress stimuli. While the current cortisol sensing methods require large laboratory settings, complex assay, and professional personnel. Herein, a novel flexible and wearable electrochemical aptasensor based on a Ni-Co metal-organic frameworks (MOF) nanosheet-decorated carbon nanotubes (CNTs)/polyurethane (PU) film is developed for rapid and reliable detection of cortisol in sweat. First, the CNTs/PU (CP) film was prepared by a modified wet spinning technology, and the CNTs/polyvinyl alcohol (PVA) solution was thermally deposited on the surface of CP film to form the highly flexible CNTs/PVA/CP (CCP) film with excellent conductivity. Then aminated Ni-Co MOF nanosheet prepared by a facile solvothermal method was conjugated with streptavidin and modified on the CCP film. Biofunctional MOF can effectively capture cortisol aptamer due to its excellent specific surface area. In addition, the MOF with peroxidase activity can catalytic oxidization of hydroquinone (HQ) by hydrogen peroxide (H 2 O 2 ), which could amplify the peak current signal. The catalytic activity of Ni-Co MOF was substantially suppressed in the HQ/H 2 O 2 system due to the formation of the aptamer-cortisol complex, which reduced the current signal, thereby realizing highly sensitive and selective detection of cortisol. The sensor has a linear range of 0.1-100 ng/mL and a detection limit of 0.032 ng/mL. Meanwhile, the sensor showed high accuracy for cortisol detection under mechanical deformation conditions. More importantly, the prepared MOF/CCP film based three-electrode was assembled with the polydimethylsiloxane (PDMS) substrate, and the sweat-cloth was used as the sweat collection channel to fabricate a wearable sensor patch for monitoring of cortisol in volunteers' sweat in the morning and evening. This flexible and non-invasive sweat cortisol aptasensor shows great potential for quantitative stress monitoring and management., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

The flexible electrochemical sensor is a key component of the health monitoring system which can continuously track the physiological signals of the human body, while there is no obvious discomfort and invasiveness. Therefore, it has great potential in personalized medical testing. However, the development of flexible electrochemical sensors currently faces many difficulties, such as the limitations of conductive material properties and manufacturing methods, and the disadvantages of commonly used flexible substrates that are not resistant to high temperatures. In this work, inorganic nanomaterials commonly used to make flexible electrochemical sensors were classified to zero-dimensional (0D) nanomaterials, one-dimensional (1D) nanomaterials, two-dimensional (2D) nanomaterials, and hybrid nanomaterials according to their morphology. The fabrication method of the nanomaterials-based flexible electrochemical sensors was also introduced. Furthermore, the application of flexible electrochemical sensors for chemical and biological sensing and their detection performance were summarized. The detection targets were classified to ion, small molecule, biomacromolecule, and bacteria, respectively., (Copyright © 2022 Elsevier B.V. All rights reserved.)

In-situ growth of CsPbBr 3 nanocrystal into Eu-BTC was realized for synthesis of dual-emission CsPbBr 3 @Eu-BTC by a facile solvothermal method, and a novel ratiometric fluorescence sensor based on the CsPbBr 3 @Eu-BTC was prepared for rapid, sensitive and visual detection of Hg 2+ in aqueous solution. The transmission electron microscopy (TEM), X-ray diffraction pattern (XRD), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) analysis were used to verify the successful incorporation of CsPbBr 3 into the Eu-BTC. Meanwhile, the CsPbBr 3 @Eu-BTC nanocomposite maintained high fluorescence performance and stability in aqueous solution. After adding Hg 2+ , the green fluorescence of CsPbBr 3 was quenched and the red fluorescence of Eu 3+ remained unchanged, while the color changed from green to red obviously. The occurrence of dynamic quenching and electron transfer were verified by fluorescence lifetime, Stern-Volmer quenching constant and XPS analysis. The ratiometric fluorescence sensor shows high analytical performance for Hg 2+ detection with a wide linear range of 0-1 μM and a low detection limit of 0.116 nM. In addition, it also shows high selectivity for the detection of Hg 2+ and can be successfully applied to detect Hg 2+ in environmental water samples. More importantly, a novel paper-based sensor based on the CsPbBr 3 @Eu-BTC ratiometric probe was successfully manufactured for the visual detection of Hg 2+ by naked eyes. This new type of ratiometric fluorescent sensor shows great potential for applications in point-of-care diagnostics., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Near-infrared (NIR) emitting Ag 2 S quantum dots (QDs) are excellent fluorescent nanoprobes for bioassays with low toxicity. A novel fluorescent sensing platform which employing NIR fluorescent Ag 2 S QDs and MnO 2 2D nanosheets as NIR emitters and quenchers is designed for rapid and selective determination of glutathione (GSH). A facile and efficient approach was demonstrated for the synthesis of NIR fluorescent Ag 2 S QDs with the emission of 845 nm. Then the NIR fluorescent nanoprobe of Ag 2 S QDs-MnO 2 nanosheets is obtained by adsorbing Ag 2 S QDs onto the surface of MnO 2 nanosheets which have atomically thick two-dimensional structure and high specific surface area. And the NIR fluorescence of Ag 2 S QDs is quenched by the MnO 2 nanosheets. The presence of GSH could reduce MnO 2 to Mn 2+ that results in the restoration of NIR fluorescence for Ag 2 S QDs. The NIR fluorescent nanoprobe could be used for highly selective detection of GSH. Also a low detection limit of 60 μmol/L was obtained. Because NIR fluorescence of the Ag 2 S QDs can efficiently reduce the interferences from background scattering and autofluorescence. The NIR fluorescent nanoprobe was directly applied to monitor the GSH level in human serum sample with high accuracy and precision., (Copyright © 2020 Elsevier B.V. All rights reserved.)

A novel NH 4 + voltammetric electrochemical biosensor was constructed by immobilizing glutamate dehydrogenase (GLDH)/Fe 3 O 4 /graphene (GR)/chitosan (CS) nanobiocomposite onto a glassy carbon electrode (GCE). On the GLDH/Fe 3 O 4 /GR/CS/GCE, GLDH catalyzed the reversible reaction, i.e., the reductive amination of α-ketoglutaric acid and the oxidative deamination of L-glutamate. The electrons produced in the enzymatic reactions were transferred to the surface of the electrode via the [Fe(CN) 6 ] 3-/4- couple, which helped for the amplification of the electrochemical signal. The electrochemical detection of NH 4 + was based on the fact that the enhanced response current was proportional to the NH 4 + concentration. Owing to the combination of the advantages of the synergistic effects of Fe 3 O 4 nanospheres, GR and CS, a promising platform for NH 4 + sensing was provided. Under optimum conditions, the introduced biosensor had a linear range of 0.4-2.0 μM for NH 4 + with the detection and quantification limits of 0.08 and 0.27 μM, respectively. Moreover, the biosensor exhibited good sensitivity and excellent reproducibility. It could retain 91.8% of its original response after two weeks of storage at 4 °C, suggesting satisfactory stability. Additionally, the proposed biosensor was successfully applied to detect NH 4 + levels in PM 2.5 samples, indicating its feasibility for application in NH 4 + monitoring in the environmental fields., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Quantitative detection of multiple chicken cytokines is a good evaluation of cell-mediated immunity in chickens after disease infection or vaccination. However, current assay methods for chicken cytokines cannot meet the needs of clinical diagnosis due to unsatisfactory sensitivity and low assay throughput. Herein, a sensitive chemiluminescence (CL) imaging immunosensor array has been developed for high-throughput detection of multiple chicken cytokines. The chicken cytokines immunosensor array was prepared by assembling different cytokine capture antibodies onto a disposable silanized glass chip, where horseradish peroxidase and antibody-conjugated gold nanoparticles were used as multienzymatic amplification probe for CL imaging signal amplification. By using a sandwich assay mode, the amplified CL signals from each sensing array cell were collected for quantitation. Using chicken interleukin-4 and chicken interferon-γ as model cytokines, this novel multiplexed and amplified method demonstrated simultaneous measurement of the two chicken cytokines in the linear ranges of 0.008-0.12 ng/mL and 0.005-0.20 ng/mL, respectively, which yields limits of detection down to 2 pg/mL and 3 pg/mL. The CL imaging array method reported here also demonstrated high specificity, good repeatability, and high stability and accuracy, providing a novel multiplex immunoassay strategy for highly sensitive and high-throughput detection of chicken cytokines and further disease diagnosis in poultry., (Copyright © 2018 Elsevier B.V. All rights reserved.)

A two-dimensional (2D) Ni based metal-organic framework (MOF) nanosheets were synthesized using a one-step solvent-thermal method. The as-prepared nanosheets were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), powder X-ray diffraction (XRD) and energy disperse spectroscopy (EDS) mapping. Ni-MOF nanosheet was first time found to used as a peroxidase mimetic with catalytic activities and could catalyze the oxidation of the substrate 3,3,5,5-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H 2 O 2 ). Catalytic mechanism analysis suggested the enzymatic kinetics of Ni-MOF nanosheets followed typical Michaelis-Menten theory and Ni-MOF nanosheets possess a higher affinity for two substrates (TMB and H 2 O 2 ) than horseradish peroxidase (HRP). Furthermore, Ni-MOF nanosheet was applied to establish an H 2 O 2 colorimetric sensor which deserves a wide linear range of 0.04 ~ 160 μM and a low detection limit of 8 nM. Also the application of this sensor for H 2 O 2 detection in human serum and disinfectant was demonstrated and satisfactory results were obtained. Thus, the simple and sensitive Ni-MOF/TMB/H 2 O 2 colorimetric system has great promising applications in clinical medicine and food environment analysis., (Copyright © 2018. Published by Elsevier B.V.)

In this work, an ultrasensitive electrochemiluminescence (ECL) method was established for the detection of trace amount of Ag ions (Ag + ). In sulfuric acid medium, Ag(II), the electro-oxidized product of Ag(I), oxidizes manganese ions (Mn 2+ ) to produce permanganate (MnO 4 - ) by using a pair of graphite catheters as electrodes. While permanganate and luminol can produce strong chemiluminescence, based on the catalytic effect of Ag(II) on Mn 2+ oxidation, there is a good linear relationship between the concentration of Ag + and luminescence intensity. Under optimized conditions, the linear range of this method for Ag + is from 0.2 to 150 nM with a detection limit of 0.06 nM. The method was applied for determination of Ag + in various water samples with satisfactory results., (Copyright © 2018 Elsevier B.V. All rights reserved.)

A nonenzymatic glucose electrochemical sensor was constructed based on Au nanoparticles (AuNPs) decorated Ni metal-organic-framework (MOF)/Ni/NiO nanocomposite. Ni-MOF/Ni/NiO nanocomposite was synthesized by one-step calcination of Ni-MOF. Then AuNPs were loaded onto the Ni-based nanocomposites' surface through electrostatic adsorption. Through characterization by transmission electron microscopy (TEM), high resolution TEM (HRTEM) and energy disperse spectroscopy (EDS) mapping, it is found that the AuNPs were well distributed on the surface of Ni-based nanocomposite. Cyclic voltammetric (CV) study showed the electrocatalytic activity of Au-Ni nanocomposite was highly improved after loading AuNPs onto it. Amperometric study demonstrated that the Au-Ni nanocomposites modified glassy carbon electrode (GCE) exhibited a high sensitivity of 2133.5 mA M -1 cm -2 and a wide linear range (0.4-900 μM) toward the oxidation of glucose with a detection limit as low as 0.1 μM. Moreover, the reproducibility, selectivity and stability of the sensor all exhibited outstanding performance. We applied the as-fabricated high performance sensor to measure the glucose levels in human serum and obtained satisfactory results. It is believed that AuNPs decorated Ni MOF/Ni/NiO nanocomposite provides a new platform for developing highly performance electrochemical sensors in practical applications., (Copyright © 2018 Elsevier B.V. All rights reserved.)

An electrochemical sensor for paracetamol based on multi-walled carbon nanotubes and chitosan-copper complex (MWCNTs/CTS-Cu) was fabricated by self-assembly technique. The MWCNTs/CTS-Cu modified GCE showed an excellent electrocatalytic activity for the oxidation of paracetamol, and accelerated electron transfer between the electrode and paracetamol. Under optimal experimental conditions, the differential pulse peak current was linear with the concentration of paracetamol in the range of 0.1-200 μmol L(-1) with a detection limit of 0.024 μmol L(-1). The sensitivity was found to be 0.603 A/mol L(-1). The proposed sensor also showed a high selectivity for paracetamol in the presence of ascorbic acid and dopamine. Moreover, the proposed electrode revealed good reproducibility and stability. The proposed method was successfully applied for the determination of paracetamol in tablet and human serum samples., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Hierarchical porous titanium dioxide (hp-TiO2) was prepared using natural magnolia grandiflora petals as templates and was further employed for the immobilization of horseradish peroxidase (HRP). Scanning electron microscopy (SEM) and nitrogen adsorption-desorption measurement revealed the wrinkled and porous structure of the obtained hp-TiO2. Fourier transform infrared spectroscopy (FT-IR) indicated the effective immobilization and conformation retention of HRP on hp-TiO2. HRP immobilized on hp-TiO2 exhibited direct, reversible, and surface-controlled redox reaction with the electron transfer rate constant of 5.46 s(-1). Furthermore, the immobilized HRP exhibited a wide linear detection range from 1.0 to 524.0 µM. The detection limit, based on a signal-to-noise ratio of 3, was down to 0.87 µM. The apparent Michaelis-Menten constant (Km(app)) of the immobilized HRP was 0.223 mM. In addition, the sensor possessed appreciable repeatability, reproducibility and remarkable stability for the sensitive determination of H2O2. Thus, this kind of hp-TiO2 can be used as an attractive material for immobilizing proteins and constructing biosensors., (Copyright © 2015 Elsevier B.V. All rights reserved.)

The accurate measurement of nitrate in PM2.5 is essential for a complete understanding of the effects of aerosols on human health, the impact of aerosols on the radiative balance of the earth and the role of aerosols in visibility problems. In this paper, we present a novel, quick, easy, cheap and eco-friendly electroanalytical procedure for the determination of nitrate in PM2.5 samples using a carbon-fiber micro-disk electrode (CFMDE) coupled with square-wave voltammetry (SWV). Under optimal experimental conditions the nitrate SWV response increases linearly with nitrate concentration over a range of 0.003-2.0 mmol L(-1), and the detection limit is 1.10 μmol L(-1) (S/N=3). Nitrate contents in daily PM2.5 of Yangzhou in China were detected successfully by employing this novel method, and the results were compared well with those obtained by using ion chromatography. Then, we detected nitrate in two-hour PM2.5 filter samples via the standard addition method, and the concentrations were applied in an analysis of the daily change of nitrate contained in PM2.5 of Yangzhou. The research in this work indicates that the electrochemical method opens a new opportunity for fast, portable, and sensitive analysis of components in PM2.5., (Copyright © 2015 Elsevier B.V. All rights reserved.)

In this work, we reported an efficient platinum nanoparticles functionalized nitrogen doped graphene (PtNPs@NG) nanocomposite for devising novel electrochemical glucose biosensor for the first time. The fabricated PtNPs@NG and biosensor were characterized using transmission electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, static water contact angle, UV-vis spectroscopy, electrochemical impedance spectra and cyclic voltammetry, respectively. PtNPs@NG showed large surface area and excellent biocompatibility, and enhanced the direct electron transfer between enzyme molecules and electrode surface. The glucose oxidase (GOx) immobilized on PtNPs@NG nanocomposite retained its bioactivity, and exhibited a surface controlled, quasi-reversible and fast electron transfer process. The constructed glucose biosensor showed wide linear range from 0.005 to 1.1mM with high sensitivity of 20.31 mA M(-1) cm(-2). The detection limit was calculated to be 0.002 mM at signal-to-noise of 3, which showed 20-fold decrease in comparison with single NG-based electrochemical biosensor for glucose. The proposed glucose biosensor also demonstrated excellent selectivity, good reproducibility, acceptable stability, and could be successfully applied in the detection of glucose in serum samples at the applied potential of -0.33 V. This research provided a promising biosensing platform for the development of excellent electrochemical biosensors., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Metal-organic frameworks composite materials have received tremendous attention because of their versatile structures and tunable porosity for various applications. Herein, amino-functionalized metal-organic frameworks (NH2-Cu3(BTC)2; BTC=benzene-1,3,5-tricarboxylate) was prepared and used as a novel electrode modifier for the determination of trace levels of lead. NH2-Cu3(BTC)2 shows quite a good capability for the efficient adsorption of lead from aqueous solutions. The parameters affecting the electrochemical process, such as electrolyte solution pH, the amount of NH2-Cu3(BTC)2 suspension, accumulation potential and accumulation time, were investigated in detail. Under the optimal conditions, the electrochemical sensor exhibited a linear response to the concentration of lead in the range of 1.0×10(-8)-5.0×10(-7) mol L(-1) (R(2)=0.9951) with a detection limit of 5.0×10(-9) mol L(-1). The relative standard deviation of 11 successive scans was 3.10% for 1.0×10(-8) mol L(-1) lead. The method was validated with certified reference material (stream sediment and milk powder) and the analytical results coincided well with the certified values. Furthermore, the method was successfully applied to the determination of target analytes in tap and lake water samples and good recoveries were obtained from different spiked values., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Nonelectroactive acetochlor can be indirectly determined through the photocatalytical degradation of acetochlor. A derivative visible light photoelectrochemical sensor for indirect detection of the herbicide acetochlor using TiO2-poly(3-hexylthiophene)-ionic liquid nanocomposite is constructed. Poly(3-hexylthiophene) (P3HT) was synthesized via chemical oxidative polymerization with anhydrous FeCl3 as oxidant, 3-hexylthiophene as monomer, chloroform as solvent, and the functional TiO2 nanoparticles were facilely prepared by blending TiO2 nanoparticles and P3HT at room temperature ionic liquid, 1-Butyl-3-methylimidazolium hexafluorophosphate solution. Operational parameters, including the photolysis time, ratios of TiO2 to P3HT, bias voltage and pH of buffer solution have been optimized. Under optimal conditions, the proposed photoelectrochemical method could detect acetochlor ranging from 0.5 to 20 μmol L(-1) with a detection limit of 0.2 nmol L(-1) at a signal-to-noise ratio of 3. The assay results of acetochlor in water samples with the proposed method were in acceptable agreement with those of the gas chromatograph-mass spectrometer (GC-MS) method. The promising sensor opens a new opportunity for fast, portable, and sensitive analysis of acetochlor in environmental samples., (Copyright © 2014 Elsevier B.V. All rights reserved.)

In this work, a novel streptavidin functionalized graphene oxide/Au nanoparticles (streptavidin/GO/AuNPs) composite is prepared and for the first time used to construct sensitive chemiluminescent immunosensor for the detection of tumor marker. The streptavidin/GO/AuNPs composite and the immunosensor are characterized using scanning electron microscopy, static water contact angle measurement and electrochemical impedance spectroscopy. The biofunctionalized composite has large reactive surface area and excellent biocompatibility, thus the capture antibody can be efficiently immobilized on its surface based on the highly selective recognition of streptavidin to biotinylated antibody. Using α-fetoprotein (AFP) as a model, the proposed chemiluminescent immunosensor shows a wide linear range from 0.001 to 0.1 ng mL(-1) with an extremely low detection limit down to 0.61 pg mL(-1). The resulting AFP immunosensor shows high detection sensitivity, fast assay speed, acceptable detection and fabrication reproducibility, good specificity and stability. The assay results of serum samples with the proposed method are in an acceptable agreement with the reference values. This work provides a promising biofunctionalized nanostructure for sensitive biosensing applications., (Copyright © 2014 Elsevier B.V. All rights reserved.)

A novel solid-phase extraction sorbent, metal-organic frameworks and graphite oxide hybrid composite, was prepared by a solvothermal technique. The morphology and properties of the resultant material were examined by Fourier transform infrared spectroscopy, X-ray diffraction and field emission scanning electron microscopy. To evaluate the extraction performance of the resultant sorbent, luteolin was chosen as a model analyte. The extraction conditions were optimized. Based on these, a convenient and efficient solid-phase extraction procedure for the determination of luteolin was established and the subsequent quantification step was performed by square wave anodic stripping voltammetry. Under the optimal conditions, the oxidation current increased linearly with increasing the concentration of luteolin in the range of 5.0 × 10(-9)-5.0 × 10(-7)molL(-1) with a correlation coefficient of 0.9983 and a detection limit of 7.9 × 10(-10)molL(-1). The relative standard deviation of seven successive scans was 4.20% for 5.0 × 10(-8)molL(-1) luteolin. This work not only proposes a useful method for sample pretreatment, but also reveals the great potential of metal-organic frameworks based hybrid materials as an excellent sorbent in solid-phase extraction., (Copyright © 2014 Elsevier B.V. All rights reserved.)

6-Benzylaminopurine (6-BA) is a kind of cytokinin which could regulate the activities of the antioxidant defense system of plants. In this work, its interaction with and inhibition of beef liver catalase have been systematically investigated using spectroscopic, isothermal titration calorimetric and molecular docking methods under physiological conditions. The fluorescence quenching of beef liver catalase (BLC) by 6-BA is due to the formation of 6-BA-BLC complex. Hydrogen bonds and van der Waals interactions play major roles in stabilizing the complex. The Stern-Volmer quenching constant, binding constant, the corresponding thermodynamic parameters and binding numbers were measured. The results of UV-vis absorption, three-dimensional fluorescence, synchronous fluorescence and circular dichroism spectroscopic results demonstrate that the binding of 6-BA results in the micro-environment change around tyrosine (Tyr) and tryptophan (Trp) residues of BLC. The BLC-mediated conversion of H2O2 to H2O and O2, in the presence and absence of 6-BA, was also studied. Lineweaver-Burk plot indicates a noncompetitive type of inhibition. Molecular docking study was used to find the binding sites., (Copyright © 2013 Elsevier B.V. All rights reserved.)

An electrochemical sensor based on a copolymer poly(4-vinylpyridine)-co-poly(acrylonitrile), P4VP-co-PAN, and Fe2O3 nanoparticle film modified glassy carbon electrode was developed for the determination of glucose. We studied the response of glucose with the proposed electrode, and determined the optimum conditions by changing the potential, pH and P4VP-co-PAN. The current response measurements were performed in PBS (c=0.1 M) with a potential of 0.7 V. The current response of this glucose sensor showed a linear relationship with the concentration in the range of 2.5 μM-0.58 mM (r=0.997). The experimental results demonstrate that this method has such merits as simple operation, low cost, high sensitivity, long term stability and good reproducibility, with satisfactory results., (Copyright © 2013 Elsevier B.V. All rights reserved.)

A sensitive and simple method using magnetic multi-walled carbon nanotubes, as an adsorbent, has been successfully developed for extraction and preconcentration trace amounts of Se(IV) with detection by hydride generation atomic fluorescence spectrometry. The prepared nanoparticles were confirmed by Fourier transform infrared spectra, X-ray diffraction spectrometry, vibrating sample magnetometry, and transmission electron microscopy. These magnetic nanocomposites can be easily dispersed in aqueous samples and retrieved by the application of external magnetic field via a piece of permanent magnet. The main factors affecting the signal intensity such as sample pH value, adsorbent amount, eluent concentration and volume, sample volume, and coexisting ions have been investigated and established. The absorbent could be repeatedly used at least 100 times. The enhancement factor of the proposed method for Se(IV) was 100. The method had a linear calibration plot in the range from 0.05 to 10.0 μg L(-1) with a standard deviation of 2.3% at 0.5 μg L(-1) (n=11). The limit of detection was as low as 0.013 μg L(-1). Accuracy of the method was evaluated by the analysis of water samples and certified reference materials., (Copyright © 2013 Elsevier B.V. All rights reserved.)

An ultrasensitive chemiluminescent (CL) immunoassay system was developed for the detection of tumor marker. This sandwich CL assay method was for the first time designed based on a highly efficient streptavidin-functionalized multi-walled carbon nanotubes (MWCNTs) platform. The glass slide was firstly silylanized with 3-gycidoxypropyltrimethoxysilane (GPTMS) to generate surface epoxy group functionality. Subsequently, the MWCNTs/chitosan solution was mixed with streptavidin solution, and a certain amount of the resulting suspension was dropped on the surface of the epoxy-activated glass substrate to form a firm streptavidin-functionalized MWCNTs platform. The biofunctionalized-MWCNTs platform shows large reactive surface area and excellent biocompatibility. The capture antibody can be efficiently immobilized on the biosensing platform surface based on the highly selective recognition of streptavidin to biotinylated antibody. Using α-fetoprotein (AFP) as model analyte, the proposed method exhibits wide linear range of 0.001-0.1 ng mL(-1) with a low detection limit down to 0.52 pg mL(-1). The CL immunoassay system displays 7.9-fold increase in the detection sensitivity compared to the immunosensor without using MWCNTs. Moreover, the resulting immunosensor demonstrates excellent specificity, good reproducibility, and acceptable stability. This streptavidin-functionalized MWCNTs platform opens a novel and promising avenue for fabricating ultrasensitive CL immunoassay system., (Copyright © 2013 Elsevier B.V. All rights reserved.)

In this paper, open-tubular capillary column coated with graphene oxide (GO) was prepared through ionic adsorption of negatively charged GO nanosheets onto the capillary wall pre-modified with positively charged poly(diallydimethylammonium chloride) (PDDA). Thus prepared coating was very stable and could endure over 200 separations. The electroosmotic flow (EOF) characteristics of bare fused silica capillary column, PDDA coated column, and GO-PDDA coated column (GO-PDDA@column) were investigated by varying the percentage of methanol in buffer and the buffer pH value. The run-to-run, day-to-day, and column-to-column reproducibilities of EOF on GO-PDDA@column were satisfying with relative standard deviation values of less than 2% in all cases. The stationary phase displays a characteristic reversed-phase behavior. The GO-PDDA@column was also used to separate proteins in egg white. Both basic and acidic proteins were separated in a single run., (Copyright © 2013 Elsevier B.V. All rights reserved.)

A novel visible light sensitized photoelectrochemical sensing platform was constructed based on the perylene-3,4,9,10-tetracarboxylic acid/titanium dioxide (PTCA/TiO(2)) heterojunction as the photoelectric beacon. PTCA was synthesized via facile steps of hydrolysis and neutralization reaction, and then the PTCA/TiO(2) heterojunction was easily prepared by coating PTCA on nano-TiO(2) surface. The resulting photoelectric beacon was characterized by transmission electron microscope, scanning electron microscopy, X-ray diffractometry, FTIR spectroscopy, and ultraviolet and visible spectrophotometer. Using parathion-methyl as a model, after a simple hydrolyzation process, p-nitrophenol as the hydrolysate of parathion-methyl could be obtained, the fabricated derivative photoelectrochemical sensor showed good performances with a rapid response, instrument simple and portable, low detection limit (0.08 nmol L(-1)) at a signal-to-noise ratio of 3, and good selectivity against other pesticides and possible interferences. It had been successfully applied to the detection of parathion-methyl in green vegetables and the results agreed well with that by GC-MS. This strategy not only extends the application of PTCA, but also presents a simple, economic and novel methodology for photoelectrochemical sensing., (Copyright © 2013 Elsevier B.V. All rights reserved.)

The graphene oxide (GO) is carbon based material that has high surface area, high adsorption ability, and is stable at high temperature. In this work, the GO phase was prepared and used for gas chromatographic separation. GO nanosheets were covalently bonded onto the inner surface of fused silica capillary column using 3-aminopropyldiethoxymethyl silane as cross-linking agent. The prepared GO nanosheets were characterized with TEM and the GO coating was characterized with SEM. As a high performance stationary phase, GO provides not only a high surface area to increase the phase ratio but also rich functional groups for the formation of hydrophobicity, hydrogen bonding, and π-π electrostatic stacking interactions with volatile aromatic or unsaturated organic compounds. Thus, mixtures of a wide range of organic compounds including alcohols and aromatic compounds were well separated and an efficiency of 1990 theoretical plates per meter for anisole was obtained on GO coated 1.0m×200μm i.d. fused silica capillary column. The experimental results demonstrate that GO coated capillary columns are promising for gas chromatographic separation., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Electrochemical impedance immunosensor, with its high sensitivity from electrochemical impedance analysis and ideal specificity from the immunoassay, is increasingly used in the detection of a kind of phenoxy acid herbicides which is 2,4-Dichlorophenoxybutyric acid (2,4-DB). In this experiment, synthetic 2,4-DB antibodies were immobilized on the electrode by the crosslinking of L-Cysteine/glutaraldehyde, and 2,4-DB were measured by the increase of electron-transfer resistance when the immune reaction occurred, with Fe(CN)(6)(3-)/Fe(CN)(6)(4-) as the probe. Under optimal conditions, the change of resistance is in a linear relationship with the logarithm of the concentration in the range of 1.0×10(-7)-1.0×10(-3) g/L (R=0.994) with the detection limit of 1.0×10(-7) g/L (0.1 ppb). This method bears such merits as simplicity in operation, high sensitivity, wide linear range, specificity, reproducibility and good stability. The actual soybean samples were analyzed with the recovery of 82.8%-102.3%., (Copyright © 2012 Elsevier B.V. All rights reserved.)

A Fe(3)O(4)/multiwall carbon nanotubes/β-cyclodextrin (Fe(3)O(4)/MWCNTs/β-CD) modified electrode, for highly sensitive and automated hypoxanthine measurements, was developed in a sequential injection lab-on-valve system. The electrochemical oxidation behavior of hypoxanthine was investigated in phosphate buffer solution by cyclic voltammetry and linear sweep voltammetry. The Fe(3)O(4)/MWCNTs/β-CD modified electrode exhibits preferably analytical characteristics in electrocatalytic activity towards the oxidation of hypoxanthine. Under optimized conditions, the log oxidation peak current intensity was proportional to log hypoxanthine concentration covering the range from 5.0×10(-8) to 1.0×10(-5) mol L(-1) with a correlation coefficient of 0.9965. A detection limit of 0.3×10(-8) mol L(-1) was achieved along with a sampling frequency of 20 h(-1). This hyphenated system offers some advantages in terms of rapidness, sensitivity and ease of manipulation. Its further applications were utilized for the determination of hypoxanthine in meat samples., (Copyright © 2012 Elsevier B.V. All rights reserved.)

A new approach to performing extraction and preconcentration employing functionalized magnetic nanoparticles for the determination of trace metals is presented. Alumina-coated iron oxide nanoparticles were synthesized and used as the solid support. The nanoparticles were functionalized with sodium dodecyl sulfate and used as adsorbents for solid phase extraction of the analyte. Extraction, elution, and detection procedures were performed sequentially in the sequential injection lab-on-valve (SI-LOV) system followed by electrothermal atomic absorption spectrometry (ETAAS). Mixtures of hydrophobic analytes were successfully extracted from solution using the synthesized magnetic adsorbents. The potential use of the established scheme was demonstrated by taking cobalt as a model analyte. Under the optimal conditions, the calibration curve showed an excellent linearity in the concentration range of 0.01-5 μg L(-1), and the relative standard deviation was 2.8% at the 0.5 μg L(-1) level (n=11). The limit of detection was 6 ng L(-1) with a sampling frequency of 18 h(-1). The present method has been successfully applied to cobalt determination in water samples and two certified reference materials., (Copyright © 2011 Elsevier B.V. All rights reserved.)

In this work, a kojic acid electrochemical sensor, based on a non-covalent molecularly imprinted polymer (MIP) modified electrode, had been fabricated in the lab-on-valve system. The sensitive layer was synthesized by cyclic voltammetry using o-phenylenediamine as the functional monomer and kojic acid as the template. The template molecules were then removed from the modified electrode surface by washing with NaOH solution. Differential pulse voltammetry method using ferricyanide as probe was applied as the analytical technique, after extraction of kojic acid on the electrode. Chemical and flow parameters associated with the extraction process were investigated. The response recorded with the imprinted sensor exhibited a response in a range of 0.01-0.2 μmol L(-1) with a detection limit of 3 nmol L(-1). The interference studies showed that the MIP modified electrode had excellent selectivity. Furthermore, the proposed MIP electrode exhibited good sensitivity and low sample/reagent consumption, and the sensor could be applied to the determination kojic acid in cosmetics samples., (Copyright © 2011 Elsevier B.V. All rights reserved.)

An ultrasensitive electrochemical method for simultaneous determination of lead and cadmium was first developed using the novel bismuth-Nafion-medical stone doped disposable electrode (an improved wax-impregnated graphite electrode). Through the synergistic sensitization effect of the resulting composite material, the disposable electrode showed remarkable electrochemical responses to lead and cadmium. The oxidation of the two metals produced two well-defined and separated square wave peaks at about -0.62 V for Pb(2+) and -0.85 V for Cd(2+), respectively. The effects of the amount of medical stone, concentration of Nafion, thickness of bismuth, pH of buffer solution, deposition potential, accumulation time, voltammetric measurement and possible interferences were investigated in detail. Under the optimal conditions, the fabricated electrode exhibited linear ranges from 2.0 to 12.0 μg L(-1) with detection limit of 0.07 μg L(-1) for lead and 2.0-12.0 μg L(-1) with detection limit of 0.47 μg L(-1) for cadmium. The assay results of heavy metals in wastewater with the proposed method were in acceptable agreement with the atomic absorption spectroscopy method., (Copyright © 2011 Elsevier B.V. All rights reserved.)

A ultrasensitive, simple and convenient electrochemical method was firstly developed for the determination of prochloraz and its metabolites as 2,4,6-trichlorophenol (2,4,6-TCP) using nano-aperture medical stone. Compared with the undoped disposable electrode (UDE), nano-aperture medical stone doped disposable electrode (MSDDE) not only significantly enhances the oxidation peak current of 2,4,6-TCP but also lowers the oxidation overpotential, suggesting that the nano-aperture MSDDE can remarkably improve the sensitivity of 2,4,6-TCP. The experimental conditions such as pH values of buffer solution, the content of nano-aperture medical stone, accumulation potential and time were optimized for the determination of 2,4,6-TCP. At optimal conditions, the oxidation peak current is proportional to the concentration of 2,4,6-TCP over the range from 6.0 × 10(-9) to 8.0 × 10(-5)mol L(-1). Finally, this novel method was successfully employed to detect prochloraz and its metabolites in orange rind with the detection limit of 8.4 × 10(-10)mol L(-1) (0.3 ng g(-1)) and the method was validated by gas chromatography., (Copyright © 2010 Elsevier B.V. All rights reserved.)

This paper reports on a new strategy to coat fused silica capillaries through ionic adsorption of gold nanoparticles (AuNPs) on a polyelectrolyte multilayer (PEM) modified capillary wall. The coating was constructed in situ by alternating rinses with positively charged poly(diallydimethylammonium chloride), negatively charged poly(sodium-4-styrenesulfonate), and positively charged AuNPs. After self-assembly of n-octadecanethiol onto the surface of AuNPs, the modified capillary was investigated as a new medium for the separation of neutral analytes and proteins in open-tubular capillary electrochromatography (OT-CEC). The surface coverage of the capillary wall was increased using the high density of AuNPs which were dynamically capped with 4-dimethylaminopyridine (DMAP). The chromatographic performance of the column coated with positively charged AuNPs was remarkably improved compared with a column modified with negatively charged AuNPs. The coating was robust over more than 810 runs in this study and also showed high stability against 0.01 M NaOH, 0.01 M HCl, and electrolyte concentrations up to 70 mM. The run-to-run, day-to-day, and capillary-to-capillary reproducibilities of electroosmotic flow were satisfying with relative standard deviation values of less than 1% in all cases. The AuNP-coated PEM modified capillary column not only showed good performance for neutral analytes but also was suitable for the analysis of both basic and acidic proteins., (Copyright © 2010 Elsevier B.V. All rights reserved.)

The analytical performance of lab-on-valve (LOV) system using irreversible biamperometry for the determination of catechol was evaluated. By integrating miniaturized electrochemical flow cell (EFC) designed and processed which is furnished with two identical polarized platinum electrodes, into the LOV unit, the lab-on-valve system combines sampling with analysis, realizing automated on-line analysis for catechol in a closed system. The biamperometric detection system was established to record the relationship between oxidation current and time by coupling the irreversible oxidation of catechol at one pretreated platinum electrode with the irreversible reduction of platinum oxide at the other pretreated platinum electrode. Factors influencing the analytical performance were optimized, including the potential difference (DeltaE), buffer solution and pH, and flow variables in the LOV. A linear calibration curve was obtained within the range of 1.0 x 10(-6)-5.0 x 10(-4) mol L(-1) of catechol with the detection limit (3 sigma) of 5.09 x 10(-7)mol L(-1). The relative standard deviation (R.S.D.) was 2.39% for 11 successive determinations of 1 x 10(-5)mol L(-1) catechol and the sample throughput was 35h(-1). Moreover, this proposed method was applied to the analysis of catechol in beer sample, which was testified by high-performance liquid chromatography (HPLC)., (Copyright (c) 2010 Elsevier B.V. All rights reserved.)

A rapid, low-cost, high sensitive and quantitative method to detect valiolamine in a medium for microbial culture, involving derivatization with a new labeling reagent, 4-methoxybenzenesulfonyl fluoride (MOBS-F), followed by reverse-phase high-performance liquid chromatography with ultraviolet (UV) detection with simple operation procedure. 4-Methoxybenzenesulfonyl chloride (MOBS-Cl) and 2-nitrobenzenesulfonyl chloride (NBS-Cl) were compared with MOBS-F as novel reagents in this paper, and the MOBS-F was chosen as the most suitable derivatization reagent. The column was thermostatic at 35 degrees C, the mobile phase flow-rate was 1.0mL/min and the detection wavelength was 240nm. For a biological sample, the separation of the derivatives was achieved using a gradient mobile system. The elution program is 88% phosphate buffer (50mM; pH=3.0) and 12% methanol for 23min, then 70% of phosphate buffer and 30% methanol for another 15min and finally 88% of phosphate buffer and 12% of methanol for 5min to re-equilibrate the column. The optimized conditions of the derivatization were as follows: derivatization reaction temperature 30 degrees C; derivatization reaction pH value 11.0, reaction time 10min and MOBS-F concentration higher than 1.5mg/mL for standard solutions and higher than 5.0mg/mL for the biological sample. Calibration curves were linear in the range of 0.050-25microg/mL for the standard solutions and 1.0-75microg/mL for the biological sample. The sensitive analytical method is helpful to control the biotechnological process of voglibose production and product quality control.

This work exploited a sequential injection lab-on-valve (LOV) system for the determination of cadmium by anodic stripping voltammetry (ASV). A miniaturized electrochemical flow cell (EFC) was fabricated in LOV, in which a nafion coated bismuth film electrode was used as working electrode. The cadmium was electrodeposited on the electrode surface in bismuth solution, and measured with the subsequential stripping scan. Under optimal conditions, the proposed system responded linearly to cadmium concentrations in a range 2.0-100.0 microg L(-1). The detection limit of this method was found to be 0.88 microg L(-1). By loading a sample volume of 800 microL, a sampling frequency of 22 determinations h(-1) was achieved. The repeatability expressed as relative standard derivation (R.S.D.) was 3.65% for 20 microg L(-1) cadmium (n=11). The established method was applied to analysis of trace cadmium in environmental water samples and the spiked recoveries were satisfactory., (Copyright (c) 2009. Published by Elsevier B.V.)

A new petentiometric method to determine peroxide hydrogen and glucose had been studied. This method had been applied on the petentiometric determination of peroxide hydrogen and glucose in the total ionic strength adjustment buffer (TISAB) (pH 7.5) solution with the glassy electrode modified by the calix[4]arene. The glassy carbon electrode covered with the calix[4]arene depended on the H(2)O(2) concentration in the range of log[H(2)O(2)] from -3.3 to -1.2 in the solution of TISAB (pH 7.5) with nearly Nernstian slope of about 65.6+/-3 mV and the detection limit of peroxide hydrogen was 4.0x10(-5) mol L(-1). The glassy carbon electrode covered with the calix[4]arene depended on the glucose concentration in the range of log[glucose] from -3.6 to -2.8 in the solution of TISAB (pH 7.5) with nearly Nernstian slope of about 50.2+/-2 mV and the detection limit of glucose was 2.0x10(-5) mol L(-1). The electrode had the good selectivity, sensitivity, stability and repeatability.

A sequential injection lab-on-valve (LOV) unit, integrating a miniaturized electrochemical flow cell (EFC), has been constructed for the determination of trace amounts of Se (IV) by employing cathodic stripping voltammetry (CSV) technique. The procedure is carried out on a mercury film coated glassy carbon electrode. The analyte solution and electrolyte solution were continuously aspirated and merged in the holding coil (HC) by using a single syringe pump, which were afterwards pushed into the EFC, where the peak current was generated during the subsequent deposition/stripping procedure and measured as the basis of quantification. Assay parameters were optimized in order to achieve the best analytical performance, including mercury film preparation, supporting electrolyte composition, deposition potential and deposition time, and flow variables in the LOV. By loading a sample volume of 500 microL, a linear calibration graph was derived within 1-600 microg L(-1), and a detection limit (3b) of 0.11 microgL(-1) was achieved along with a sampling frequency of 20 h(-1). By integrating the EFC into the LOV unit, the assembling system not only minimized the sample/reagent consumption and waste generation, but also enhanced the sampling frequency. The work itself extended the applications of electrochemical detection techniques and provided a good platform for Se (IV) electrochemical analysis.

Sequential injection lab-on-valve (LOV) was first proposed for analyzing ultra-trace amounts of Pb using differential pulse anodic stripping voltammetry (DPASV) with a miniaturized electrochemical flow cell fabricated in the LOV unit. Deposition and stripping processes took place between the renewable mercury film carbon paste electrode and sample solution, the peak current was employed as the basis of quantification. The mercury film displayed a long-term stability and reproducibility for at least 50 cycles before next renewal, the properties of integrated miniature LOV unit not only enhanced the automation of the analysis procedure but also declined sample/reagent consumption. Potential factors that affect the present procedure were investigated in detail, i.e., deposition potential, deposition time, electrode renewable procedure and the volume of sample solution. The practical applicability of the present procedure was demonstrated by determination of Pb in environmental water samples.

Amidosulfonic acid was electropolymerized by cyclic voltammetry onto the surface of glassy carbon electrode (GCE) to fabricate the chemically modified electrode, which showed high stability, good selectivity and reproducibility for determination of isoniazid. The modified electrode showed an excellent electrocatalytical effect on the oxidation of isoniazid. Under the optimum conditions, there was a good linear relationship between anodic peak current and isoniazid concentration in the range of 5.0 x 10(-8)- 1.0 x 10(-5) M, and a detection limit of 1.0 x 10(-8) M (S/N = 3) was obtained after 120 s at the accumulation potential of - 0.2 V (vs. SCE). This developed method had been applied to the direct determination of isoniazid in injection and tablet samples with satisfactory results.

The electrochemical oxidation of L-cysteine (CySH) in presence of carbon nanotubes (CNTs) formed a composite film at a glassy carbon electrode (GCE) as a novel modifier for directly electroanalytical determination of terbinafine without sample pretreatment in biological fluid. The determination of terbinafine at the modified electrode with strongly accumulation was studied by differential pulse voltammetry (DPV). The peak current obtained at +1.156 V (vs. SCE) from DPV was linearly dependent on the terbinafine concentration in the range of 8.0 x 10(-8)-5.0 x 10(-5 )M in a B-R buffer solution (0.04 M, pH 1.81) with a correlation coefficient of 0.998. The detection limit (S/N=3) was 2.5 x 10(-8 )M. The low-cost modified electrode showed good sensitivity, selectivity, and stability. This developed method had been applied to the direct determination of terbinafine in human serum samples with satisfactory results. It is hopeful that the modified electrode will be applied for the medically clinical test and the pharmacokinetics in future.

The effect of a divalent cation (Mg2+) and 3 monovalent cations (Na+, Li+, and K+) as buffer additives on the electroosmotic flow (EOF) was investigated in order to improve the separation performance of p-acetamidobenzenesulfonyl fluoride (PAABS-F) derivatives of 20 standard amino acids by micellar electrokinetic chromatography (MEKC). The EOF can be decreased with increasing concentration of cations with the order of cations as Mg2+>K+>Na+>Li+. However, it was found that the resolution cannot be improved easily using a buffer cation which is more capable of decreasing the EOF. Taking the migration time, resolution, and peak shape into account, Na+ is the best buffer additive, although the EOF decreased most using Mg2+. Using 20 mmol/L borate at pH 9.3 containing 140 mmol/L SDS and 20 mmol/L Na+ as electrolyte, 20 standard amino acids were successfully separated within 14 min.

A novel one-step approach to glassy carbon nanoelectrode ensembles (NEEs) with the pores of 20-120nm in radii has been developed using an amphiphilic block copolymer [polystyrene-block-poly (acrylic acid)] self-assembly. This procedure is simple and fast, and requires only conventional, inexpensive electrochemical instrumentation. Electrochemical methods were used to characterize the NEEs prepared using this new procedure. The NEEs drastically suppressed the response of ascorbic acid (AA) and resolved the overlapping voltammetric response of uric acid (UA) and AA into two well-defined peaks with a large anodic peak difference (DeltaE(pa)) of about 310mV. The peak current obtained from differential pulse voltammetry (DPV) was linearly dependent on the UA concentration in the range of 0.25-50microM at neutral pH (PBS, pH 6.86) with a correlation coefficient of 0.999, and the detection limit was 0.04microM (S/N=3). The NEEs has also been demonstrated to be applicable in the detection of UA in serum and urine samples with excellent sensitivity and selectivity. The NEEs will hopefully be of good application for further sensor development.

A new ultraviolet (UV) labeling reagent, p-acetamidobenzenesulfonyl fluoride (PAABS-F), was designed and synthesized to label and determine the amino acids by capillary electrophoresis (CE) with diode-array detector (DAD). PAABS-F is very stable and easy to synthesize. It reacted with primary or secondary amino acids very quickly under facile conditions to give corresponding derivatives in high yield with excellent sensitivity and stability. No by-products were observed in amino acid derivatives when stored at room temperature under natural daylight for at least 7 days. Both amino acids standard solution and real samples reacted with this new UV labeling reagent smoothly to form high UV-absorption derivatives. The labeled 20 standard amino acids were efficiently separated by CE and the mass detection limits (S/N=3) were ranged from 59.3 fmol for L-tryptophan to 1.70 pmol for L-histidine.

A new and simple method for fabricating controllable insulated nanometer-sized platinum electrodes is presented. Electrochemical etching of platinum wire is employed, and then a repeated process of cycle voltammetric deposition of electrophoretic paint and heat curing for shrink film follows which effectively controls the size of the nanoelectrodes, which is different from previous DC electrolysis deposition. This technique allows complete insulation of the whole body of the etched platinum wire, except for the very tip with the shrink film during heat curing of the film, leaving an electrochemical active area with effective diameters of nanometers. The process overcomes the pinhole formation resulting from the electrophoretic paint deposition process. The size of the platinum electrodes and the thickness of the deposed paint for insulation can be properly controlled and reproduced. The fabricated electrodes show ideal steady-state voltammetric behaviors from which the effective areas of the nanoelectrodes are measured. The effective radius of the prepared nanoelectrodes ranges from 3.1nm to hundreds of nanometers.

Time-resolved fluorescence has been developed for immunoassay to obtain higher sensitivity than usual immunoassays. In this paper, a simple, sensitive and specific method was developed for immunoassay of serum carcinoembryonic antigen (CEA) by combining time-resolved fluoroimmunoassay (TRFIA) and flow injection analysis. Based on a sandwich immunoassay format, a monoclonal antibody immobilized immunoaffinity column inserted in a flow system was used for immunoreactions. The cleaved solution was collected after the reaction between the immunocomplex in the immunoaffinity column and the enhancement solution that was used to cleave the Eu-labels from the immunocomplex, and then detected by time-resolved fluorescence. Serum CEA could be detected in the linear range from 2.5 to 100 ng/ml with a correlation coefficient of 0.997 and the detection limit of 1.0 ng/ml. Twenty human serum samples detected by this method were in good agreement with the results obtained by the electrochemiluminescence immunoassay. This method could be further developed for fast practical clinical detection of serum CEA levels.

A novel chemiluminescent immunosensor for carbohydrate antigen 19-9 (CA19-9) based on the immobilization of CA19-9 on the cross-linked chitosan membrane was developed. The different membranes were characterized by atomic force microscopy (AFM) and infrared spectrum, respectively. Based on a noncompetitive immunoassay format, this proposed chemiluminescent immunosensor enabled a low-cost, flexible and rapid determination for CA19-9 in combination with flow injection analysis (FIA). After an off-line incubation of the analyte CA19-9 with horseradish peroxidase (HRP)-labeled anti-CA19-9, the mixture was injected into the immunosensor, which led to the trapping of free HRP-labeled anti-CA19-9 by the immobilized antigen in the immunosensor. The trapped HRP-labeled antibody was detected by chemiluminescence due to its catalytic activity following the reaction of luminol and H2O2. Under optimal conditions, the decreased chemiluminescent signal of the immunosensor was proportional to the CA19-9 concentration in the range of 2.0-25 U/ml with a detection limit of 1.0 U/ml. The immunosensor showed an acceptable accuracy and good reproducibility. The results of 20 human serum samples detected by this method were in acceptable agreement with those obtained by immunoradiometric assay. The proposed immunosensor provided a new promising tool for practical clinical detection of the serum CA19-9 level.

A novel immunosensor for rapid separation-free determination of carcinoembryonic antigen (CEA) in human serum is proposed. The immunosensor is prepared by co-immobilizing thionine and horseradish peroxidase (HRP)-labeled CEA antibody on a glassy carbon electrode (GCE) through covalently binding them to GCE with a glutaraldehyde (GA) linkage. The electrochemical behavior of the immobilized thionine displays a surface-controlled electrode process with an average electron transfer rate constant of 4.74+/-2.99 s(-1). It can be used as an electron transfer mediator for enzymatic activity detection of the HRP-labeled antibody to CEA. After the immunosensor is incubated with CEA solution at 23 degrees C for 40 min, the access of activity center of the HRP to thionine is partly inhibited, which leads to a linear decrease in the catalytic efficiency of the HRP to the oxidation of immobilized thionine by H(2)O(2) at -300 mV over two CEA concentration ranges from 0.5 to 3.0 and 3.0 to 167 ng/ml. Under optimal conditions, the detection limit for the CEA immunoassay is 0.1 ng/ml at three times background noise. The immunosensor shows good accuracy and acceptable storage stability, precision and reproducibility with intra-assay CVs of 6.1% and 5.8% at 2.5 and 50 ng/ml CEA, respectively, and an inter-assay CV of 6.3% at 50 ng/ml. This method is economical and shortens the analytical time, making it potentially attractive for clinical immunoassays.