ascorbic-acid and 1-2-diaminobenzene

Topics: Alkaline Phosphatase; Ascorbic Acid; Cobalt; Colorimetry; Fluorescent Dyes; Humans; Hydroxides; Limit of Detection; Metal Nanoparticles; Oxidation-Reduction; Phenylenediamines; Point-of-Care Testing; Smartphone

A target-dependent ratiometric fluorescence sensing strategy was designed and fabricated based on a redox reaction for highly sensitive detection of α-glucosidase (α-Glu) activity and its inhibitor. In this study, silicon quantum dots (SiQDs) with excellent optical properties and two-dimensional (2D) cobalt oxyhydroxide (CoOOH) nanosheets were successfully prepared and exploited for the detection of analytes. The CoOOH nanosheets are able to oxidize o-phenylenediamine (OPD), and the product 2,3-diaminophenazine (oxOPD) not only quenches the blue fluorescence of SiQDs (440 nm) by the inner filter effect (IFE) but also emits orange fluorescence (565 nm). α-Glu can catalytically hydrolyze l-ascorbic acid-2-O-α-d-glucopyranosyl (AA2G) to produce ascorbic acid (AA). The redox between AA and CoOOH could lead to the damage of CoOOH nanosheets, thereby inhibiting the oxidization of OPD and effectively preserving the fluorescence of SiQDs. Thus, ratiometric detection of α-Glu activity was achieved according to the AA-dependent dual-fluorescence signal responses. Under the optimal conditions, good linearity was obtained in the range of 0.01-6 U mL-1 with a detection limit of 0.004 U mL-1. The IC50 of α-Glu inhibitor acarbose was estimated to be 0.216 μM. The method provides high sensitivity and selectivity for the determination of α-Glu activity and its inhibitor, which has great application potential in clinical diagnosis and anti-diabetic drug screening. Furthermore, a logic gate analytical device was successfully established based on double fluorescence signals, which makes it possible to monitor α-Glu activity by intelligence equipment.

Topics: Acarbose; alpha-Glucosidases; Ascorbic Acid; Cobalt; Fluorescence; Glycoside Hydrolase Inhibitors; Humans; Logic; Nanostructures; Oxidation-Reduction; Oxides; Phenylenediamines; Quantum Dots; Silicon

A ratiometric fluorescent assay is fabricated for the evaluation of alkaline phosphatase (ALP) activity. This assay is composed of ionic liquid-functionalized carbon dots (IL-CDs) with blue fluorescence signal at 470 nm and 2,3-diaminophenazine (DAP) with yellow fluorescence signal at 570 nm. IL-CDs were synthesized via electrochemical method by using ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) and ultrapure water as precursors. DAP is produced by the oxidation reaction between o-phenylenediamine and H

Topics: Alkaline Phosphatase; Armoracia; Ascorbic Acid; Carbon; Fluorescent Dyes; Horseradish Peroxidase; Humans; Hydrogen Peroxide; Imidazoles; Ionic Liquids; Limit of Detection; Phenylenediamines; Quantum Dots; Spectrometry, Fluorescence

Large-scale epidemiological studies have shown a close correlation between adverse human health effects and exposure to ambient particulate matter (PM). The oxidative potential (OP) of ambient PM has been implicated in inducing toxic effects associated with PM exposure. In particular, reactive oxygen species (ROS), either bound to PM or generated by particulate components in vivo, substantially contribute to the OP and therefore toxicity of PM by lowering antioxidant concentrations in the lung, which can subsequently lead to oxidative stress, inflammation, and disease. Traditional methods for measuring aerosol OP are labor intensive and have poor time resolution, with significant delays between aerosol collection and ROS analysis. These methods may underestimate ROS concentrations in PM because of the potentially short lifetime of some ROS species; therefore, continuous online, highly time-resolved measurement of ROS components in PM is highly advantageous. In this work, we develop a novel online method for measuring aerosol OP based on ascorbic acid chemistry, an antioxidant prevalent in the lung, thus combining the advantages of continuous online measurement with a physiologically relevant assay. The method limit of detection is estimated for a range of atmospherically important chemical components such as Cu(II) 0.22 ± 0.03 μg m

Topics: Aerosols; Ascorbic Acid; Bicyclic Monoterpenes; Copper; Dehydroascorbic Acid; Electrochemical Techniques; Fluorescent Dyes; Iron; Limit of Detection; Oxidation-Reduction; Particulate Matter; Phenylenediamines; Reactive Oxygen Species

Inspired by the special reducing capability of ascorbic acid (AA), ascorbic acid 2-phosphate (AA2P) has been extensively utilized as a substrate in current alkaline phosphatase (ALP) activity assays owing to the ALP-triggered transformation of AA2P into AA. However, such assays usually require AA-related complicated and laborious synthesis and/or signal generation procedures. Herein, we report an interesting in situ fluorogenic interaction between o-phenylenediamine (OPD) and AA, which inspires us to put forward a novel and simple AA2P/OPD-participated fluorescence turn-on ALP activity assay for the first time, and then the corresponding ALP-based fluorescence enzyme-linked immunosorbent assay (ELISA) has also been developed by means of the conventional ELISA platforms. According to the convenient and facile detection process with clear response mechanism, our fluorogenic reaction-based assay exhibits good sensitivity, selectivity, and excellent sensing performance, which ensures fluorescence ELISA to potentially be applied in clinical diagnosis by employing a well-studied biomarker of hepatocellular carcinoma, α-fetoprotein (AFP) as the model analyte. Such original ELISA via in situ formation of fluorophore from scratch gives a new sight to develop other potential immunoassay platforms in early clinical diagnosis by controlling the target antigens in the near future.

Topics: Alkaline Phosphatase; Ascorbic Acid; Carcinoma, Hepatocellular; Enzyme-Linked Immunosorbent Assay; Fluorescence; Fluorescent Dyes; Humans; Liver Neoplasms; Molecular Structure; Phenylenediamines

In recent years, α-glucosidase (α-Glu) inhibitor has been widely used in clinic for diabetic and HIV therapy. Although different systems have been constructed for sensitive and selective detection of α-Glu and screening its inhibitor, the method based on ratiometric fluorescence for α-glucosidase inhibitor screening remains poorly investigated. Herein, we constructed a new MnO

Topics: Acarbose; alpha-Glucosidases; Ascorbic Acid; Biomimetic Materials; Enzyme Assays; Fluorescent Dyes; Glycoside Hydrolase Inhibitors; Limit of Detection; Manganese Compounds; Metal Nanoparticles; Oxides; Oxidoreductases; Phenazines; Phenylenediamines; Silver; Spectrometry, Fluorescence

In this paper, we compare and evaluate the applicability of three UV-VIS absorbance based assays for high-throughput quantification of ascorbic acid in horticultural products. All the methods involve the use of a common enzyme (ascorbate oxidase) in combination with a different indicator molecule. The three methods were retrieved from literature: a direct oxidase-method, an OPDA coupled oxidase-method and a PMS-method, which is commercially available. The analysis in high-throughput context involved the analysis in microplates in combination with the use of an automated liquid handling system. We checked (i) the performance factors of the selected methods on standard solutions, (ii) the applicability of the defined methods in high-throughput context, and, (iii) the accuracy of the methods on real samples using HPLC as a reference technique. The OPDA-method was found to be the most appropriate method for the quantification of ascorbic acid in high-throughput context with a linear range between 7.0 and 950 mgL(-1) and excellent correlation parameters (slopes close to 1, intercepts close to 0, R(2)>0.91) with the reference technique when real samples were analyzed. Finally, this method was optimized for assay cost and assay time. Hereto the enzymatic reaction was mathematically described using a model for enzyme kinetics, which was then used to calculate the optimal concentrations of ascorbate oxidase and OPDA. As a result of the modeling the amount of enzyme in the assay could be reduced with a factor 2.5 without affecting significantly the reaction time. In a last step the optimal concentrations were used for a successful validation with the HPLC-reference technique.

Topics: Ascorbate Oxidase; Ascorbic Acid; Chromatography, High Pressure Liquid; Fruit; Kinetics; Methylphenazonium Methosulfate; Phenylenediamines; Reproducibility of Results; Sensitivity and Specificity; Spectrophotometry, Ultraviolet; Time Factors; Vegetables

We developed a novel, cost-effective, and automated assay for ascorbic acid (AsA) in serum using a COBAS MIRA S analyzer (Roche Diagnostic System). Our method has a wide dynamic range and covers AsA concentrations from well below the lower reference interval to well above it. AsA is oxidized by 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy, free radical (TEMPO) to dehydroascorbic acid (DAsA). The latter condenses with o-phenylenediamine (OPDA) to form a quinoxaline derivative that absorbs light at 340 nm. The change in absorbance at 340 nm is proportional to the concentration of AsA in the specimen. The automated system permitted the assay of 65 specimens per hour at a cost of approximately US$ 0.01 per specimen for reagents. The assay can be applied directly to serum specimens (direct method) and also to sera with a prior deproteinization step with metaphosphoric acid. The detection limit for the direct serum assays is 0.8 vs. 0.4 mg/l with the deproteinization method. The recovery of AsA from a supplemented serum pool was of >95% for both procedures. We used four distinct methods on 66 patients sera. The direct method for AsA correlated well with an HPLC method (r=0.964, P<0.001); the direct method also correlated well with a method that uses AsA oxidase (r=0.975, P<0. 001). The deproteinization method correlated well with HPLC (r=0.981, P<0.001), and with the AsA oxidase procedure (r=0.994, P<0.001). Ten within-day determinations on a serum pool gave a C.V. <4.3% for both the direct and deproteinization procedures. The between-day assays of the same serum pool over 10 days gave a C.V. of <6.7% by both methods.

Topics: Artifacts; Ascorbic Acid; Automation; Chromatography, High Pressure Liquid; Cyclic N-Oxides; Electrochemistry; Free Radicals; Phenylenediamines; Reference Standards; Reproducibility of Results

A simple and rapid analysis of total ascorbic acid (AsA) in serum and plasma and its automated analysis are described. AsA is oxidized by ascorbate oxidase (AsA oxidase) to dehydroascorbic acid that then reacts with o-phenylenediamine (OPDA) to form a quinoxaline derivative that absorbs at 340 nm. The change in absorbance is directly proportional to the total AsA concentration. The assay was validated with a linear concentration range of 0.8-80 mg/L, and the within-day and between-day assays precision did not exceed 8.6% and 12.5%, respectively. On 47 sera, the manual enzymatic procedure gave 0.2 mg/L on average lower values than those of an automated enzymatic procedure with a correlation coefficient of 0.847. On another 66 sera, results by automated enzymatic method correlated well with the HPLC method and the regression equation is Y (enzymatic, automated)=0.97 X (HPLC)+0.1, r=0.980, Sy.x=0.6 mg/L. An experienced analyst can perform about 24 manual assays per hour whereas the automated procedure gave a rate of 100 assays per hour.

Topics: Ascorbate Oxidase; Ascorbic Acid; Automation; Chromatography, High Pressure Liquid; Oxidation-Reduction; Phenylenediamines; Reproducibility of Results; Sensitivity and Specificity; Time Factors

Given the widespread interest in antioxidant nutrients, we have developed a new procedure that will permit the automated determination of plasma ascorbic acid (AA) concentration with a Roche Fara centrifugal analyzer. After the deproteinization of plasma with metaphosphoric acid, AA is oxidized to dehydroascorbic acid by AA oxidase. The product is coupled to o-phenylenediamine to produce a chromophore for which the absorbance is measured at 340 nm. The procedure allows much faster throughput than conventional HPLC methods while yielding results that correlate well and provide improved precision. Linearity extends beyond the reference range of 26.1-84.6 micromol/L, and severe hemolysis is the only interference identified.

Topics: Adult; Ascorbate Oxidase; Ascorbic Acid; Autoanalysis; Chromatography, High Pressure Liquid; Dehydroascorbic Acid; Female; Humans; Male; Phenylenediamines; Quality Control; Reference Values; Sensitivity and Specificity; Spectrophotometry

We demonstrate that total ascorbic acid (TAA, the sum of ascorbic acid and dehydroascorbic acid) in properly prepared human plasma is stable at -70 degrees C for at least 6 years when preserved with dithiothreitol. TAA in human plasma or serum preserved with metaphosphoric acid degrades slowly, at the rate of no more than 1% per year. As assessed from our stability data and from data obtained from 23 laboratories over a period of > 2 years, the intralaboratory repeatability of TAA measurement is approximately 2 mumol/L, irrespective of TAA concentration. Nonchromatographic analytical methods involving dinitrophenylhydrazine and 0-phenylenediamine yield biased results relative to chromatographic methods. Within groups of laboratories that use roughly similar analytical methods, the interlaboratory measurement reproducibility CV for TAA is 15%.

Topics: Ascorbic Acid; Chromatography; Dehydroascorbic Acid; Dithiothreitol; Drug Stability; Freezing; Humans; Kinetics; Laboratories; Phenylenediamines; Phenylhydrazines; Phosphorous Acids; Plasma; Reproducibility of Results; Specimen Handling; Stereoisomerism; Time Factors

Human plasma glycerol was determined with a microdialysis electrode, containing the enzymes glycerol kinase and glycerol phosphate oxidase held stationary within the electrode. A microdialysis electrode is essentially a conventional microdialysis probe, with a platinum working electrode inserted into the tip of the dialysis fiber and reference and counter electrodes contained in the upper compartment. The linear range of response to glycerol was directly dependent on the concentration of ATP. At 4 mM ATP, the linear range was 0.5-500 microM. A fast response time of 20 s was obtained. Two types of interferences were observed when plasma glycerol was measured: direct oxidation of interferents at the electrode and attenuation of response to glycerol by reaction with hydrogen peroxide and/or poisoning of the platinum electrode. Ascorbate, urate, and acetaminophen were removed from plasma samples by a pretreatment step involving peroxidase and catalase. Any remaining interferent current was reduced by electropolymerizing o-phenylenediamine onto the platinum electrode. Adsorption of plasma proteins on the dialysis fiber was minimal and was not reduced by the preadsorption of human serum albumin. Very good correlation was obtained between the electrode and the standard spectrophotometric technique for the variation in glycerol concentration with time.

Topics: Absorption; Acetaminophen; Adenosine Triphosphate; Ascorbic Acid; Biosensing Techniques; Blood Proteins; Buffers; Glycerol; Glycerol Kinase; Glycerolphosphate Dehydrogenase; Humans; Hydrogen Peroxide; Hydrogen-Ion Concentration; Microdialysis; Oxidation-Reduction; Phenylenediamines; Platinum; Uric Acid

Exposure of the respiratory mucosa to oxygen-enriched air contributes to the generation of the lung damage in both adult respiratory distress syndrome and bronchopulmonary dysplasia. Recent work has identified the nasal submucosal gland as the source of diverse molecules important in mucous membrane host defense. We searched for the presence of antioxidant activity in nasal glandular secretions, the absence of which could possibly predispose to oxygen-induced injury. Employing a low molecular weight preparation of nasal secretions (a pooled concentrate passed over a 10,000-dalton molecular sieve), antioxidant activity capable of inhibiting both horseradish peroxidase and Fenton reagent reactions was discovered. The following lines of evidence suggest that submucosal glands are the source of this activity. (1) Antioxidant activity present in resting, baseline nasal washings is significantly increased after cholinergic stimulation either in response to topical methacholine or induced by a gustatory reflex. (2) Application of atropine reduced the antioxidant activity to baseline levels after either of the cholinergic stimuli. (3) Levels of antioxidant activity correlated very closely with the secretion of lactoferrin, a recognized product secreted solely from the serous cell of the submucosal gland. The antioxidant activity is due to novel, previously unrecognized molecules. This activity is found in nasal secretions containing molecules less than 10,000 daltons, is unaffected by N-ethyl maleimide (which inactivates glutathione, another low molecular weight antioxidant), is not associated with the capacity to reduce cytochrome c (as seen with ascorbic acid), and resides in the water soluble pool of secretions (in contrast to vitamin E, another putative antioxidant).(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Ascorbic Acid; Atropine; Cholinergic Fibers; Enzyme-Linked Immunosorbent Assay; Exocrine Glands; Glutathione; Horseradish Peroxidase; Humans; Hydrogen Peroxide; Lactoferrin; Luminescent Measurements; Methacholine Chloride; Nasal Mucosa; Nasal Provocation Tests; Oxygen; Phenylenediamines; Reflex; Sulfhydryl Compounds