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Simultaneous and Ratiometric Electrochemical Determination of Uric Acid and Hypoxanthine Based on In Situ Carbonized Polydopamine Graphene Paper
... Purine metabolism abnormalities, including excess hypoxanthine levels, can be causally associated with metabolic disorders such as Lesch-Nyhan syndrome [5]. Since the presence of HXA in our extracellular fluids has caused some diseases, including xanthinuria, goat, urolithiasis, joint inflammation, hyperuricemia, kidney failure, Alzheimer's, etc., because of these reasons, the detection and quantity measurement of HXA has become increasingly important [3,6]. Also, fish and chicken foods are important elements of a healthy diet, and global requirements are increasing for fresh and packed meat foodstuffs. ...
This work presents the detection of hypoxanthine (HXA), a purine derivative that is similar to nucleic acids who overconsumption can cause health issues, by using hydrothermally synthesized cerium phosphate (CePO4) followed by a sonochemical approach for CePO4 decorated with a functionalized carbon nanofiber (CePO4@f-CNF) nanocomposite. The formation of the nanocomposite was confirmed with X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). A CePO4@f-CNF nanocomposite is used to modify a glassy carbon electrode (GCE) to analyze the electrochemical detection of HXA. Cyclic voltammetry (CV), Electrochemical impedance spectroscopy (EIS), and Differential pulse voltammetry (DPV) were used to examine the electrochemical properties of the composite. As a result, the modified electrode exhibits a larger active surface area (A = 1.39 cm2), a low limit of detection (LOD) at 0.23 µM, a wide linear range (2.05–629 µM), and significant sensitivity. Therefore, the CePO4@f-CNF nanocomposite was used to study the real-time detection in chicken and fish samples, and it depicted significant results.
A Cr-based metal-organic framework MIL-101(Cr) was used to load platinum nanoparticles (PtNPs) that were placed on a glassy carbon electrode (GCE). The modified GCE was used as a non-enzymatic xanthine sensor. Compared to bare GCE, it requires a strongly decreased working potential and an increased signal current for xanthine oxidation. This is due to the crystalline ordered structure and large specific surface of the MIL-101(Cr), and to the high conductivity of the Pt NPs. Differential pulse voltammetry (DPV) shows the sensor to have a wide linear range (0.5 – 162 μM), a low detection limit (0.42 μM), and high selectivity. It was applied to the simultaneous determination of dopamine, uric acid, xanthine and hypoxanthine at working potentials of 0.13, 0.28, 0.68 and 1.05 V, respectively (vs. Ag/AgCl) and to quantify xanthine in spiked serum samples.
Graphical abstractThis is the first report of non-enzymatic xanthine electrochemical sensor based on metal-organic framework loaded with nanoparticles.
In this study, an effective and simple direct printing method was developed to create sensing devices on screen-printed carbon electrodes (SPCEs) to detect multiple species simultaneously. Two sensing materials, graphene oxide nanoribbons (GONRs) and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), were printed on one SPCE for detection of multiple biochemical substances. Printed layers of the GONRs and PEDOT:PSS mixture (GONRs & PEDOT:PSS) on SPCE showed embedment of GONRs in the PEDOT:PSS layer and diminished the electrochemical activity of GONRs. In contrast, by printing the GONRs and PEDOT:PSS at separate locations (GONRs + PEDOT:PSS) on the same SPCE, the electrochemical activities of both GONRs and PEDOT:PSS can be preserved. Thus, without synthesizing new materials, the modified electrode is able to simultaneously detect ascorbic acid (AA), uric acid (UA), dopamine (DA), and nitrite (NO2–), with high anodic oxidation currents and well-separated voltammetric peaks, in differential pulse voltammetry measurements. The detection limits for the four analytes are 41 nM (AA), 30 nM (DA), 11 nM (UA), and 18 nM (NO2–), respectively. The electrode can either detect single species separately or simultaneously determine specific concentrations of the four species in aqueous mixtures, and this can be further extended for many other electrochemical sensing applications.
Interest in electrochemical analysis of purine nucleobases and few other important purine derivatives has been growing rapidly. Over the period of the past decade, the design of electrochemical biosensors has been focused on achieving high sensitivity and efficiency. The range of existing electrochemical methods with carbon electrode displays the highest rate in the development of biosensors. Moreover, modification of electrode surfaces based on nanomaterials is frequently used due to their extraordinary conductivity and surface to volume ratio. Different strategies for modifying electrode surfaces facilitate electron transport between the electrode surface and biomolecules, including DNA, oligonucleotides and their components. This review aims to summarize recent developments in the electrochemical analysis of purine derivatives, as well as discuss different applications.
Thin carbonized polydopamine (C-PDA) coatings are found to have similar structures and electrical conductivities to those of multilayered graphene doped with heteroatoms. Greatly enhanced electrochemical properties are achieved with C-PDA-coated SnO(2) nanoparticles where the coating functions as a mechanical buffer layer and conducting bridge.
Graphitic-like carbon nitride/graphene oxide composite nanosheets (g-C3N4/GO) were synthesized for simultaneous determination of uric acid (UA) and dopamine (DA). The surface features and electrochemical properties of the g-C3N4/GO were investigated by scanning electron microscopy, X-ray diffraction, cyclic voltammetry and electrochemical impedance spectra. The voltammetric responses of UA and DA were determinated by cyclic voltammetry and differential pulse voltammetry. g-C3N4/GO had significantly improved electrical conductivity, selective oxidation capacity and electrocatalytic activity. The proposed g-C3N4/GO modified glassy carbon electrode (GCE) consequently displayed excellent electrocatalytic activity for UA and DA, with a broad linear detection range (0.03–30 μM) and extremely low detection limits (UA 4.6 nM; DA 5.4 nM). The proposed g-C3N4/GO/ GCE also demonstrated excellent reproducibility, selectivity and stability. The levels of UA and DA in human serum were measured by the g-C3N4/GO/GCE, and then the known concentrations of UA and DA were spiked to the samples, which proved that the recoveries were good.
Background and Aims
Studies have shown that elevated serum uric acid (SUA) may increase the risk of coronary heart disease (CHD). However, it was still disputable how mediate effects between metabolic diseases and hyperuricemia affect the incidence of CHD. This study aimed to explore whether metabolic diseases may mediate the connection from hyperuricemia at baseline to the elevated incidence risk of CHD during follow-ups.
Methods and Results
Based on the Jinchang cohort, 48 001 subjects were followed for 9 years between June 2011 and December 2019. Multivariate-adjusted Cox regression models were applied to estimate hazard ratios (HRs) of CHD with 95% confidence intervals (CIs). Significantly increased risks of CHD were observed in hyperuricemia (HR:1.46, 95%CI:1.28, 1.67) when compared with normouricemia population. The mediating effect model further demonstrated that metabolic diseases could mediate the association between hyperuricemia and CHD pathogenesis, partially for the combined metabolic diseases with mediation effects of 45.12%, 25.24% for hypertension, 28.58% for overweight or obese status, 29.05% for hypertriglyceridemia, 6.70% for hypercholesterolemia, 3.52% for low high density lipoprotein cholesterol (HDL-C), and 6.51% for high low density lipoprotein cholesterol (LDL-C), respectively.
Conclusions
Hyperuricemia significantly increased the risk of incident CHD, and this association was partly mediated by metabolic diseases.
Gout is an autoinflammatory disease caused by the deposition of urate crystals. As the most common inflammatory arthritis, gout has a high incidence and can induce various severe complications. At present, there is no effective cure method in the world. With the deepening of medical research, gout drug treatment continues to progress. In this review, we provide a landscape view of the current state of the research on gout treatment drugs, including the research progress of anti-inflammatory and analgesic drugs, drugs that promote uric acid excretion, and drugs that inhibit uric acid production. We mainly emphasize the understanding of gout as an auto-inflammatory disease and the discovery strategy of related gout drugs to provide a systematic and theoretical basis for the new exploration of gout drug discovery.
Uric acid (UA) is the end product of purine derivatives in human metabolism. Both low and high levels of UA lead to a various number of disorders such as Wilson’s disease, hypertension, cardiovascular diseases, kidney-related diseases. The normal range of UA in human blood serum should be fall between 0.13-0.46 mM and 1.49-4.46 mM in urine. The present review article highlights the various electrochemical biosensors developed for uric acid monitoring, with special emphasis on enzymatic and non-enzymatic methods. The enzymatic biosensors showed a concentration range between 100-10⁷ nM and limit of detection from 0.52-5×10⁹ nM whereas non– enzymatic biosensors showed concentration range in between 1-9×10⁵ nM and limit of detection in range of 0.1-700 nM. These biosensors computed UA levels in various biological and pharmaceutical samples. Future perspectives for better improvement and commercialization of UA biosensors are also conferred.
Spectrophotometry is an economic and rapid method for detecting oxalic acid (OA), while the reported methods have some drawbacks, such as narrow linear range, long response time, delicate operation and required expensive reagents. Herein, we found that the as-synthesized Fe(III)-sulfosalicylate (FeSSA) could be used as an efficient colorimetric chemosensor to detect OA, and the established FeSSA-based fading spectrophotometry showed prominent advantages over the existing ones in detecting OA. The as-established method has wider linear range of 0.80-160 mg/L with regression coefficient ≥ 0.999, while the widest linear range is just 2.7-54 mg/L among the reported ones. Moreover, the method has low limit of detection (0.74 mg/L), extremely fast response (several seconds), satisfactory selectivity, high accuracy and precision. Most importantly, its reliability was further verified by employing it to determine OA concentration during the degradation process of organic pollutants. The measured OA concentration at any time interval was perfectly consistent with those determined by the well-recognized high performance liquid chromatography (HPLC). These confirmed that the FeSSA-based fading spectrophotometry is an efficient, simple, fast, accurate and economic method to determine OA in a wide concentration range.
Uric acid is a precipitating factor for gout and renal disease, and regular monitoring of uric acid concentration is essential for health management. Hence, accurate measurement is indispensable for clinical diagnosis. Reference measurement procedures (RMP) is an essential element to ensure accuracy and comparability of tested results. In this study, the optimization of a candidate RMP (cRMP) adopting isotope dilution coupled with liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS) method for human serum uric acid measurement has been developed. The accuracy of this cRMP was validated by measuring certified reference materials (CRMs) and participating in the external quality assessment (EQA) scheme initiated by International Federation of Clinical Chemistry (IFCC) and National Center for Clinical Laboratory (NCCL). Biases were −0.64-1.51%, which were within the required equivalent limit. Excellent precision was obtained with intra- and inter-assay CVs of 0.42–0.73% and 0.20–0.43%, respectively. The limit of detection (LOD) and limit of quantification (LOQ) was determined to be 0.24 and 1.19 μmol/L, respectively. A good liner response was obtained ranged from 30.0 to 895 μmol/L. Compared with the previous RMP for uric acid, the much easier one-step protein precipitation method without further evaporation, the simplified isocratic elution of chromatographic separation condition, and the shorter analysis running time in only 5 min allowed simpler and faster analysis. Moreover, this optimized cRMP was also applied for value assignment of clinical serum samples covered a wide concentration range of serum uric acid and also obtained a decent calibration and measurement capability (CMC).
An efficient molecularly imprinted polymer (MIP) voltammetric sensor is prepared based on polypyrrole (PPy) imprinted film-bearing poly(3,4-ethylenedioxythiophene):polystyrene sulfonate-functionalized black phosphorene (BP-PEDOT:PSS) for the selective recognition and robust determination of norfloxacin. BP-PEDOT:PSS was prepared via a simple ultrasonic-assisted liquid-phase exfoliation as an efficient support for use in MIP electrochemical sensors. The imprinted PPy film was deposited onto the surface of BP-PEDOT:PSS via the potentiodynamic technique in the presence of norfloxacin, with the imprinting factor of 3.86 for norfloxacin. The morphologies and microstructures of the sensing materials were investigated using scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, and Raman spectroscopy. Additionally, parameters including the BP-PEDOT:PSS loading volume, norfloxacin:pyrrole molar ratio, electropolymerization cycles, template removal, solution pH, and time of electrode exposure to the analyte were optimized. Under optimal conditions, the response peak currents of norfloxacin correlated linearly to norfloxacin concentrations from 0.001 to 10 μM, with a limit of detection of 0.25 nM. The prepared imprinted sensor could effectively distinguish norfloxacin from other fluoroquinolone antibiotics with the selectivity coefficients of 5.4 − 17.3 and maintained stable, robust voltammetric responses for up to two weeks. Moreover, it successfully detected norfloxacin in pharmaceutical formulations and milk samples.
Norfloxacin (NOR) is an antibiotic commonly used to treat humans and food-producing animals. Owing to NOR abuse, its residues are frequently found in animal-derived food products and the surrounding environment. Therefore, development of an efficient analytical technique for the selective determination of trace NOR is greatly significant for food safety and environmental protection. Here, we fabricated an ultrasensitive, label-free molecularly imprinted polymer (MIP) voltammetric sensor for the selective determination of NOR, based on an Au nanoparticle-functionalized black phosphorus nanosheet nanocomposite (BPNS-AuNP) covered by a polypyrrole-imprinted film. BPNS-AuNP nanocomposites were prepared via an in-situ one-step method without the use of reducing agents. The polypyrrole imprinted film was formed on the surface of the BPNS-AuNPs in the presence of NOR. The physical properties and electrochemical behavior of the MIP/BPNS-AuNPs were investigated using various characterization techniques, and the analytical parameters were optimized. We found that BPNS-AuNPs improve the ambient stability and electrocatalytic activity, providing a large surface area for locating a higher number of specific recognition sites. Consequently, the MIP/BPNS-AuNP/GCE showed excellent sensing performance toward NOR, with a wide linear response range (0.1 nM − 10 μM), an extremely low limit of detection (0.012 nM), and extraordinary selectivity. Moreover, the MIP/BPNS-AuNP/GCE was used to determine NOR in various experimental samples with satisfactory results.
Simultaneous determination of multiple heavy metal ions (HMIs) at trace level is of great significance for the environmental protection. Herein, a cost-effective voltammetric sensor was designed for the simultaneous determination of toxic Cd(II) and Pb(II) using shuttle-like α-Fe2O3 nanoparticles decorated β-Bi2O3 microspheres. After introducing the Fe2O3/Bi2O3 nanocomposites, the electroactive surface area and roughness factor increased significantly. The Fe2O3/Bi2O3 nanocomposites exhibited superior electrocatalytic activity than other modified electrodes, probably because the synergistic interaction between Fe2O3 and Bi2O3 greatly facilitated the deposition-stripping process. The Fe2O3/Bi2O3/GCE realized the simultaneous determination of nanomolar Cd(II) and Pb(II) with a wide dynamic range of 0.002 − 4 μM. Moreover, the Fe2O3/Bi2O3 nanocomposites showed robust stability in the voltammetric responses up to three weeks and excellent selectivity against the potential interfering such as metal ions and biomolecules. The Fe2O3/Bi2O3/GCE was successfully employed to simultaneously detect Cd2+ and Pb2+ from water and milk samples with good recovery.
The purpose of gout treatment is to alleviate symptoms of flares, prevent flares from recurring by lowering serum urate, and minimize structural joint damage and functional impairment. In recent years, several new medications to treat gout have been developed, and novel agents continue to be investigated, in addition to several long-established treatments. Although a number of effective therapies are available, optimal management and outcomes are frequently not achieved due to physician under prescribing of urate-lowering therapy (ULT) and poor adherence with therapy when it is prescribed. This article reviews recent developments in the management of gout with reference to recently published clinical guidelines, outlines some important questions regarding the safety and efficacy of particular agents, and remaining gaps in our knowledge about the most effective strategies for using currently available treatments.
A nanocomposite of ZnO nanorods and electro-reduced graphene oxide (ZnONRs/ERGO) was prepared as cost-effective and efficient electrocatalyst for voltammetric detection of dopamine via a facile hydrothermal treatment followed by an electrochemical reduction. The ZnONRs were uniformly supported on the surface of conductive ERGO nanosheets, which enlarged the electroactive surface area and lowered the electron transfer resistant significantly. As a result, ZnONRs/ERGO modified glass carbon electrode (ZnONRs/ERGO/GCE) showed much more remarkable electrocatalytic activity toward dopamine oxidation than the controlled electrodes, with amplified response current and decreased over-potential. The extraordinary electrocatalytic activity is mainly attributed to the synergistic catalytic effects from ZnONRs and ERGO nanosheets. Using second derivative linear voltammetry (SDLSV), two wide dynamic response ranges (0.01 to 6.0 μM and 6.0 to 80 μM) were achieved at the ZnONRs/ERGO/GCE with an extremely low limit of detection (LOD) of 3.6 nM. The ZnONRs/ERGO/GCE also demonstrates excellent anti-interference ability and good repeatability, reproducibility as well as stability. Moreover, the ZnONRs/ERGO/GCE realized the accurate detection of dopamine concentration in human serum with good recoveries. Considering the outstanding advantages including low cost, simple manufacture, high efficiency, and superior sensing properties, ZnONRs/ERGO shows tremendous application prospects on real detection of catecholamine neurotransmitters.
Green emissive N,P co-doped carbon dots (N,P-CDs) were prepared by a simple hydrothermal method from citric acid, urea, and phosphoric acid as carbon, nitrogen and phosphorous pre-sources, respectively. The prepared N,P-CDs were applied to establish a dual-mode colorimetric and fluorometric sensor for monitoring - uric acid based on in situ formation of Ag shell on the surface of AuNPs. We observed that the fluorescence intensity of N,P-CDs was quenched by adding AuNPs due to overlap between the emission peak of N,P-CDs and surface plasmon resonance peak (SPR) of AuNPs. With adding Ag⁺ and uric acid, the SPR peak intensity of AuNPs increased due to the reduction of Ag⁺ to Ag⁰ and Ag shell formation on the surface of AuNPs. Also, a blue shift in the SPR peak position of AuNPs was observed at the higher concentration of uric acid, resulting in the color variation of the solution from red to orange. These variations in the SPR peak intensity and position caused more fluorescence quenching of N,P-CDs because of the increasing spectral overlap between N,P-CDs and [email protected] We indicated that there is a logarithmic relationship between increasing SPR peak intensity of AuNPs as well as fluorescence quenching of N,P-CDs and uric acid concentration in the range of 0.1-10 and 0.5-10 μM, respectively. Regarding the mentioned facts, we developed a dual colorimetric and fluorometric sensor to determine uric acid. The detection limit was 40 and 400 μM for colorimetric and fluorometric methods, respectively. The established sensor was exploited for uric acid analysis in human urine samples.
Redox homeostasis between hypochlorous acid (HClO/ClO-) and ascorbic acid (AA) significantly impacts many physiological and pathological processes. Herein, we report a new electrochemical sensor for the simultaneous determination of HClO and AA in body fluids. We first coated a carbon fiber microelectrode (CFME) with a three-dimensional nanocomposite consisting of graphene oxide (GO) and carbon nanotubes (CNTs) to fabricate the CFME/GO-CNT electrode. After the electrochemical reduction of GO (ERGO), we integrated a latent 1-(3,7-bis(dimethylamino)-10H-phenothiazin-10-yl)-2-methylpropan-1-one (MBS) electrochemical molecular recognition probe to monitor HClO and employed anthraquinone (AQ) as an internal reference. The compact CFME/ERGO-CNT/AQ + MBS sensor enabled the accurate and simultaneous measurement of HClO and AA with excellent selectivity and sensitivity. Measurements were highly reproducible, and the sensor was stable and exceptionally biocompatible. We successfully detected changes in the redox cycles of HClO and AA in human body fluids. This sensor is a significant advance for the investigation of reactions involved in cellular redox regulation. More importantly, we have devised a strategy for the design and construction of ratiometric electrochemical biosensors for the simultaneous determination of various bioactive species.
In the present work, polydopamine nanotubes (PDA NTs) decorated with silver (Ag) nanoparticles (NPs) were successfully fabricated via a template induced self-polymerization of dopamine, followed by in situ reduction and immobilization of NPs from nitrate solution. The typical [email protected] NTs exhibits 39.1 wt % of Ag content and excellent catalytic activity as demonstrated by the reduction of a model organic pollutant, methylene blue, with an apparent rate constant of 3.19 min–1 in the first-order kinetics model, which is the highest value reported so far. The superior catalytic performance is attributed to the high Ag loading, uniform distribution of NPs, and excellent dispersity in water. Moreover, it is believed that the superhydrophilic hollow morphology of PDA NTs with ultrahigh porosity (81.4%) and open ends facilitates the contact of the catalysts with reactant molecules and mass transfer in aqueous reaction. The [email protected] NTs nanocatalysts could be easily recycled, and the catalytic efficiency remained nearly unchanged over 10 cycles. This synthetic strategy was proved to be applicable to other typical metal catalysts (e.g., Pt, Pd, Au). This work presents a universal approach to fabricate highly efficient nanocatalysts with PDA NTs as supports used for the reduction and degradation of organic dyes.
Herein, we report on a sensitive probe for colorimetric detection of uric acid based on the formation of Ag shell on Au nanorods (Ag/AuNRs) in the presence of uric acid. Uric acid can reduce Ag⁺ to Ag atoms which deposit on the surface of AuNRs and form Ag shell. As a result of this phenomenon, the dielectric environment around AuNRs changes and the longitudinal surface plasmon resonance (SPR) peak of AuNRs blue-shifts, leading to the change of solution color from purple to green. Based on these facts, a colorimetric sensor for the detection of uric acid in the concentration range of 0.1–1.0 µM with a detection limit of 0.065 µM was developed. The method was applied for analysis of uric acid in human plasma and urine samples with satisfactory results. The sensor can be used for uric acid detection even with bare eyes.
Carbon paper electrodes are employed for different electrochemical applications such as flow batteries and fuel cells. However, redox reactions such as VO<sup>2+</sup>/VO<sub>2</sub><sup>+</sup> in a vanadium redox flow battery have been found to possess relatively slow kinetics, resulting in significant activation losses during operation. In this work, we demonstrate a facile and scalable method for nitrogen doping of carbon paper electrodes, leading to superior electrocatalytic activity. The effect of pyrolytic pretreatments under different conditions on the performance of carbon paper were also studied to elucidate their electrocatalytic activity from a material physics perspective, using Raman spectroscopy. The 2D Raman signature, a specific feature of the carbon structures, was employed to understand the effect of different pretreatments on the Fermi level of the carbon papers, which could help us elucidate their intrinsic electron transfer kinetics. The full wave half maximum of the 2D Raman band, and the intensity ratio I<sub>2D </sub>/ I<sub>G</sub> were used to indicate changes in the Fermi level relative to the untreated carbon paper, and hence the electrocatalytic properties, which were confirmed using voltammetric techniques. Although heating of carbon paper in air at around 500°C (a widely used method for activating carbon paper electrodes) increases the surface area by about 16-times compared to untreated and nitrogen-doped carbon paper, the latter exhibits superior electrocatalytic property for VO<sup>2+</sup>/VO<sub>2</sub><sup>+</sup>, [Fe(CN)<sub>6</sub>]<sup>3−/4−</sup>, and the oxygen reduction reaction. This study provides greater physical insights into different pretreatments in terms of the energy barrier at the interface, which will aid the pursuit for better carbon-based electrode materials and provide mechanistic details about charge transfer processes at the interface.
A representative mesoporous metal–organic-framework (MOF) material, NU-1000, has been rendered electronically conductive via a robust inorganic approach that permits retention of MOF crystallinity and porosity. The approach is based on condensed-phase grafting of molecular tin species onto the MOF nodes via irreversible reaction with hydroxyl and aqua ligands presented at the node surface, a self-limiting process termed Solvothermal Installation (of metal ions) in MOFs (SIM, a solution-phase analog of atomic layer deposition in MOFs). Treatment of the modified MOF with aerated steam at 120 oC converts the grafted tin molecules to tetra-tin(IV)oxy clusters, with the clusters being sited between insulating pairs of zirconia-like nodes (the zirconium component being key to endowing the parent material with requisite chemical and thermal stability). By introducing new O-H presenting ligands on the modified-MOF node, the high-temperature steam step additionally serves to reset the material to reactive form, thus enabling a second self-limiting tin grafting step to be run (and after further steam treatment, enabling a third). Difference-envelop-density (DED) analyses of synchrotron-derived X-ray scattering data, with and without installed tin species, show that the clusters formed after one cycle are spatially isolated, but that repetitive SIM cycling adds metal and oxygen ions in a way that enshrouds nodes, links clusters, and yields continuous 1D strands of oxy-tin(IV), oriented exclusively along the c ¬axis of the MOF. Two-probe conductivity measurements show that the parent MOF and the version containing isolated oxy-tin(IV) clusters are electrically insulating, but that the versions featuring continuous strands show an electrical conductivity of 1.8 x 10-7 S/cm after three Sn-SIM cycles. When combined with interdigitated microelectrodes, the solvent-free and conductive-glass-modified material (three Sn-SIM cycles) displays a substantial and persistent increase in electrical conductivity during exposure to 5% H2, indicating a role for dissociated H2 as an electronic dopant. The increase can be repetitively reversed by alternating H2 with air, illustrating the ability of the conductive MOF to function as a resistive sensor for H2 and suggesting further potential applications that may capitalize on the combination of high volumetric surface area, high mesoporosity, high chemical and thermal stability, and significant electrical conductivity.
Mussel-inspired polydopamine (PDA) particles with the size of ~270 nm have been employed as support of Pd nanoparticles (NPs) for catalyst preparation. Surface morphology of the PDA particle has been controlled via corrosion of CF3COOH. Surface chemistry of the obtained PDA particle has been engineered by the formation of carboxylic acid terminated alkanethiol monolayer. The obtained monolayer-modified PDA (SAM-PDA) particles are used to load Pd NPs by simply adding H2PdCl4 solution to a suspension of SAM-PDA particles at room temperature. TEM, EDX mapping, DLS, XRD, XPS, UV-vis and FTIR have been employed to characterize the catalyst and investigate the process. Uniform Pd NPs (2-3 nm) have been well dispersed on SAM-PDA particles via surface engineering. Surface morphology is modified by the corrosion of CF3COOH. Surface charge and interactions with metal ion are regulated by the monolayer of carboxylic acid. The obtained Pd/SAM-PDA catalyst has shown greatly increased activity and good reusability compared with Pd/PDA in the reduction of 4-nitrophenol (4-NP) by sodium borohydride or H2. The surface chemistry of PDA has been finely engineered for efficient loading of noble metal NPs. The kinetic data of 4-NP hydrogenation catalyzed by Pd/SAM-PDA are fitted to a Langmuir-Hinshelwood (L-H) model, and the apparent activation energy of this process has been calculated.
A simple and sensitive double injection/single detector flow injection analysis (FIA) method is proposed for the simultaneous kinetic determination of ascorbic acid (AA) and uric acid (UA). This method is based upon the difference between the rates of the AA and UA reactions with Fe3 + in the presence of 1, 10-phenanthroline (phen). The absorbance of Fe2 +/1, 10-phenanthroline (Fe-phen) complex obtained as the product was measured spectrophotometrically at 510 nm. To reach a good accuracy in the differential kinetic determination via the mathematical manipulations of the transient signals, different criteria are considered in the selection of the optimum conditions. The multi criteria decision making (MCDM) approach is applied for the selection of the optimum conditions. The importance weights of the evaluation criteria are determined using the analytic hierarchy process, entropy method, and compromised weighting (CW). The experimental conditions (alternatives) are ranked by the technique for order preference by similarity to an ideal solution. Under the selected optimum conditions, the analytical signals obtained were linear in the ranges of 0.50–5.00 and 0.50–4.00 mg L− 1 for AA and UA, respectively. The 3σ detection limits were 0.07 mg L− 1 for AA and 0.12 mg L− 1 for UA. The relative standard deviations for four replicate determinations of AA and UA were 2.03% and 3.30% respectively. The method was also applied for the analysis of analytes in the blood serum, Vitamine C tablets, and tap water with satisfactory results.
In current work highly sensitive and stable electrochemical sensor for simultaneous detection of ascorbic acid (AA), dopamine (DA), and uric acid (UA) is constructed based on the hierarchical nanoporous (HNP) PtTi alloy. The HNP-PtTi alloy is simply fabricated by two-step dealloying process, characterized by the bimodal ligament/pore size distributions and interconnected hollow channels. The HNP structure with the advantages of large surface area, excellent structure stability, and rich pore channels is used for facilitating the electron conductivity and the mass transfer. Combined with the dual effects of the bimodal nanoporous architecture and the excellent electrocatalytic activity of PtTi alloy, the constructed sensor exhibits high electrochemical sensing activity with wide linear responses from 0.2 to 1mM, 0.004 to 0.5mM, and 0.1 to 1mM for simultaneous detection of AA, DA, and UA, respectively. In addition, HNP-PtTi alloy also shows long-term sensing stability towards the AA, DA, and UA detection and behaves as a good anti-interference towards NaCl, KCl, FeCl3, CuCl2, AlCl3, glucose, and H2O2. The HNP-PtTi alloy manifests intriguing application potential as the candidate for the application of the electrochemical sensor for simultaneous detection of AA, DA, and UA.
Kohlenstoff-Filme: Dopamin wurde als Vorstufe für die einfache und kontrollierte Erzeugung eines stark dehnbaren, transparenten und elektrisch leitenden Films verwendet (siehe Bild). Der Film ist transparent und kann reversibel mechanischen Deformationen widerstehen (wie z. B. Dehnung um 20 % in 100 Durchgängen).
AbstractA large mesoporous carbon modified glassy carbon electrode (LMC/GCE) was prepared. The morphology and structure of the LMC were characterized. The LMC/GCE was used to investigate the electrochemical behaviors of metabolites of purine nucleotide, uric acid (UA), xanthine (XA) and hypoxanthine (HX). The LMC/GCE exhibited high electrocatalytic activity towards the three compounds when compared with those obtained at the GCE. Furthermore, the LMC/GCE realized simultaneous determination of UA, XA and HX at a physiological pH of 7.0 with wide linear range and low detection limit. The electrocatalytic activity of the LMC/GCE towards guanine (G) and adenine (A) was also investigated.
Carbon-based films: Dopamine was used as the precursor for the facile yet controllable production of a highly stretchable transparent conductive film. The film synthesized is transparent and can reversibly withstand mechanical deformations (such as being stretched to 20 % for 100 cycles).
The determination of uric acid in urine shows clinical importance, once it can be related to human organism dysfunctions, such as gout. An analytical procedure employing a multicommuted flow system was developed for the determination of uric acid in urine samples. Cu(II) ions are reduced by uric acid to Cu(I) that can be quantified by spectrophotometry in the presence of 2,2′-biquinoline 4,4′-dicarboxylic acid (BCA). The analytical response was linear between 10 and 100 μmol L− 1 uric acid with a detection limit of 3.0 μmol L− 1 (99.7% confidence level). Coefficient of variation of 1.2% and sampling rate of 150 determinations per hour were achieved. Per determination, 32 μg of CuSO4 and 200 μg of BCA were consumed, generating 2.0 mL of waste. Recoveries from 91 to 112% were estimated and the results for 7 urine samples agreed with those obtained by the commercially available enzymatic kit for determination of uric acid. The procedure required 100-fold dilution of urine samples, minimizing sample consumption and interfering effects. In order to avoid the manual dilution step, on-line sample dilution was achieved by a simple system reconfiguration attaining a sampling rate of 95 h− 1.
Serum uric acid may be an independent risk factor for cardiovascular disease. This review examines this association, potential mechanisms, and explores whether strategies to reduce uric acid will improve outcomes. The recent studies of xanthine oxidase inhibition are given particular focus. Epidemiological evidence supports the theory that uric acid is an independent risk factor for cardiovascular disease. Recent studies of losartan, atorvastatin and fenofibrate suggest that uric acid reduction contributes to the risk reduction offered by these therapies. Several small studies of xanthine oxidase inhibition have shown improvements in measures of cardiovascular function of a similar magnitude to that of other proven preventative treatments. These trial data and the convincing epidemiological evidence mandate that large clinical trials of uric acid-lowering strategies are performed in patients with or at high risk of cardiovascular disease. If such approaches are shown to be effective in reducing cardiovascular events, they would represent a novel and cost-effective preventative approach.
Febuxostat, a nonpurine selective inhibitor of both the oxidized and reduced forms of xanthine oxidase, was approved in February 2009 by the US Food and Drug Administration for the management of hyperuricemia in adults with gout. Objective: The purpose of this review was to summarize available information about the clinical use of febuxostat, including its chemistry, pharmacology, pharmacokinetics, pharmacodynamics, clinical efficacy, and safety profile.
A search of the medical literature using PubMed (1949-August 2009) and the Iowa Drug Information Service (1966-August 2009) was performed to identify all published articles about febuxostat. Key search terms included febuxostat, hyperuricemia, gout, TMX-67, and TEI-6720. Articles were limited to those published in English. Reference lists of the primary set of articles identified were reviewed for pertinent articles and scientific meeting abstracts not identified in the original search.
A total of 88 published articles (including 14 human studies) were identified in the original search. Review of the references of these 88 articles yielded 7 additional trials published in abstract form. Clinical trial data from this review were obtained from these 21 studies. Dose-dependent reductions from baseline in serum urate occur with febuxostat. Clinical trials found that 40 mg/d of febuxostat was noninferior to conventionally dosed allopurinol (300 mg/d) in the percentage of subjects achieving the primary end point of serum urate <6.0 mg/dL (45% for febuxostat vs 42% for allopurinol), whereas 80 mg/d of febuxostat was reported to be superior (67% vs 42%; P < 0.001). Febuxostat 40 and 80 mg/d appeared to be well tolerated in the populations studied, with adverse events mostly limited to liver enzyme elevations (6.6% and 4.6%, respectively), nausea (1.1% and 1.3%), arthralgias (1.1% and 0.7%), and rash (0.5% and 1.6%). Febuxostat does not require dosage adjustment in patients with mild to moderate renal impairment (creatinine clearance, 30-89 mL/min). Because of the risk of acute gout flares occurring when febuxostat treatment is initiated, concomitant therapy with colchicine or an NSAID for >or=8 weeks is recommended.
Febuxostat is the first agent marketed in the United States to treat hyperuricemia of gout since allopurinol was approved in 1964. In English-language published clinical trials, it was found to be noninferior to allopurinol and generally well tolerated.
A simple and sensitive method based on capillary electrophoresis (CE) with chemiluminescence (CL) detection has been developed for the determination of uric acid (UA). The sensitive detection was based on the enhancement effect of UA on the CL reaction between luminol and potassium ferricyanide (K3[Fe(CN)6]) in alkaline solution. A laboratory-built reaction flow cell and a photon counter were deployed for the CL detection. Experimental conditions for CL detection were studied in detail to achieve a maximum assay sensitivity. Optimal conditions were found to be 1.0 x 10(-4) M luminol added to the CE running buffer and 1.0 x 10(-4) M K3[Fe(CN)6] in 0.2 M NaOH solution introduced postcolumn. The proposed CE-CL assay showed good repeatability (relative standard deviation [RSD]=3.5%, n=11) and a detection limit of 3.5 x 10(-7) M UA (signal/noise ratio [S/N]=3). A linear calibration curve ranging from 6.0 x 10(-7) to 3.0 x 10(-5) M UA was obtained. The method was evaluated by quantifying UA in human urine and serum samples with satisfactory assay results.
The simultaneous encapsulation of a coupled uricase-peroxidase system and amplex red in a sol-gel matrix allows one to obtain a reagent-less and ready-to-use fluorescent biosensor for the accurate detection of uric acid in highly diluted biological fluids. The detection limit of the prepared biosensor was found to be 20 nM and was linear up to 1 microM. The high sensitivity found for the biosensor permitted a reliable determination of uric acid concentrations in the presence of interfering species (e.g., ascorbic acid) just by sample dilution (up to 50000 for urine and 10000 for serum and blood). The sol-gel encapsulation preserved the hierarchy of the enzyme activity as demonstrated by the performance of the fluorescent biosensor.