| 1. |
- Amine, A., et al.
(författare)
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A Microdialysis probe coupled with a miniaturized thermal glucose sensor for in vivo monitoring
- 1995
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Ingår i: Analytical Letters. - : Informa UK Limited. - 0003-2719 .- 1532-236X. ; 28:13, s. 2275-2286
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Tidskriftsartikel (refereegranskat)abstract
- A miniaturized thermal flow injection analysis biosensor has been coupled with a microdialysis probe for continuous subcutaneous glucose monitoring. Thermal biosensors are based on the principle of measuring the heat evolved during enzyme catalysed reactions. The system presented here consists of a miniaturized thermal biosensor with a small column containing coimmibolized glucose oxidase and catalase. The analysis buffer passes through the column at a flow rate of 60μL/min via an 1μL sample loop which is connected to a microdialysis probe. Invitro results showed constant permeability of the probe and stability of the biosensor response during 24 hours. The response time was 85 sec giving a sample rate of 42 samples/hour. During a load experiment, the glucose profile in a healthy volunteer was followed both in the subcutaneous tissue and blood using the microdialysis set-up proposed and comparing to blood glucose analyser.
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| 2. |
- Bhattachayay, Dipankar, et al.
(författare)
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Electrochemical acetylcholine chloride biosensor using an acetylcholine esterase biomimic
- 2008
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Ingår i: Analytical Letters. - : Taylor andamp;amp; Francis. - 0003-2719 .- 1532-236X. ; 41:8, s. 1387-1397
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Tidskriftsartikel (refereegranskat)abstract
- Pure enzymes are costly and highly sensitive to change in pH, temperature, ionic strength etc. Hence biomimetic or synthetic enzymes could be useful alternatives to such natural proteins. Although the selectivity of a biomimic is somewhat less than that of enzyme, it can be used as a detector element in inexpensive but stable biosensors. An organic compound, 4-[(1E)-ethanehydrazonoyl]benzoic acid, has been designed and synthesized as biomimic for the enzyme acetylcholine esterase. An acetylcholine chloride two-electrode screen-printed sensor was first developed using the immobilized enzyme acetylcholine esterase. The performance of the mimic in the hydrolysis of acetylcholine chloride was then tested with the same transducer by immobilizing the biomimic in place of the enzyme. The response of the sensor constructed using the mimic was comparable to that of the pure acetylcholine esterase enzyme electrode.
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| 3. |
- BIFULCO, L, et al.
(författare)
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TTF-MODIFIED BIOSENSORS FOR HYDROGEN-PEROXIDE
- 1994
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Ingår i: Analytical Letters. - : Taylor andamp;amp; Francis. - 0003-2719 .- 1532-236X. ; 27:8, s. 1443-1452
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Tidskriftsartikel (refereegranskat)abstract
- Amperometric biosensors for hydrogen peroxide were produced, based on TTF-modified graphite disc electrodes, incorporating immobilised peroxidase. At the optimum operating potential (-200 mV vs. calomel electrode), a Linear response to hydrogen peroxide was obtained in the range 0-2 mM (Km value = 1.98 mM). Low sensitivity to pH fluctuations and good stability at room temperature were exhibited.
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| 4. |
- Bång, Joakim, et al.
(författare)
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Stereoisomeric separation of derivatised 2-alkanols using gas chromatography – mass spectrometry: sex pheromone precursors found in pine sawfly species
- 2012
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Ingår i: Analytical Letters. - : Informa UK Limited. - 0003-2719 .- 1532-236X. ; 45:9, s. 1016-1027
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedStereoisomers of long-chain secondary alcohols are used as sex pheromone precursors among pine sawflies and some species can be severe pine forest pests. To use their pheromone in environmentally friendly pest management, methods are needed that can determine the stereochemistry of the precursor alcohols. Combinations of 11 acid chloride derivatives and 10 GC columns were evaluated for separation of stereoisomers of 3,7-dimethylundecan-2-ol, 3,7-dimethyldodecan-2-ol, 3,7-dimethyltridecan-2-ol, 3,7-dimethyltetradecan-2-ol, and 3,7-dimethylpentadecan-2-ol. Derivatization with (S)-2-acetoxypropionyl chloride in combination with a Chiraldex B-PA column separated all eight stereoisomers of 3,7dimethylundecan-2-ol, 3,7-dimethyldodecan-2-ol, and 3,7-dimethyltridecan-2-ol. A combination of two different derivatization methods was needed to separate all stereoisomers of the longer chained alcohols 3,7-dimethyltetradecan-2-ol and 3,7-dimethylpentadecan-2-ol. A female extract of the pine sawfly Neodiprion lecontei was also analyzed and the stereochemistry of the sex pheromone alcohol precursor was determined to be (2S,3S,7S)-3,7-dimethylpentadecan-2-ol at an amount of about 7 ng/female. This paper presents the first GC-MS separation of all eight stereoisomers of 3,7-dimethylundecan-2-ol, 3,7dimethyldodecan-2-ol, and 3,7-dimethyltridecan-2-ol in a single analytical run and also the first GC-MS determination of the stereochemistry of the sex pheromone precursor found in females of N. lecontei.
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| 5. |
- Dasenaki, Marilena, et al.
(författare)
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Simultaneous Determination of Free Cortisol, Cortisone and their Tetrahydrometabolites in Urine by Single Solvent Extraction and Liquid Chromatography-Tandem Mass Spectrometry
- 2019
-
Ingår i: Analytical Letters. - : Taylor & Francis. - 0003-2719 .- 1532-236X. ; 52:17, s. 2764-2781
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Tidskriftsartikel (refereegranskat)abstract
- A fast, efficient and low-cost high performance liquid chromatography-tandem mass spectrometry methodology was developed and validated for the simultaneous determination of free urinary cortisone, cortisol and their tetrahydro-metabolites. The developed method comprises a simple liquid-liquid extraction with CH2Cl2, followed by reversed-phase liquid chromatography-tandem mass spectrometry (LC-MS/MS) with electrospray ionization (ESI) in positive mode. The baseline chromatographic separation of the analytes, including the stereoisomers tetrahydrocortisol (THF) and allo-THF, was achieved on a Hypersil Gold C-18 column with a mobile phase consisting of 0.05%v/v formic acid in water-acetonitrile, using a gradient elution program. The influence of the mobile phase composition and the ESI parameters on the sensitivity of the method was extensively studied. Sample preparation was also optimized, testing two techniques: solid phase extraction (SPE) and liquid-liquid extraction (LLE). Recoveries ranged from 74.7% (a-THF) to 93.5% (cortisol) and the method limits of detection (MLD) ranged from 0.34 ng mL(-1) (cortisol) to 1.37 ng mL(-1) (THF). Intra- and inter-day coefficient of variation of the assay varied from1.5% (allo-THF) to 13% (tetrahydrocortisone) and from 3.6% (allo-THF) to 14.9% (tetrahydrocortisone), respectively. The method was applied for the analysis of urine samples from 53 healthy individuals with a mean age of 13.96 years in order to estimate the concentration of the five corticosteroids and the ratio of the metabolites. Associations between urinary cortisol/cortisone and serum cortisol/cortisone values were also characterized.
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| 6. |
- Gao, Leihong, et al.
(författare)
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Determination of Melamine in Fresh Milk with Hollow Fiber Liquid Phase Microextraction Based on Ion-Pair Mechanism Combined with High Performance Liquid Chromatography
- 2012
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Ingår i: Analytical Letters. - : Informa UK Limited. - 0003-2719 .- 1532-236X. ; 45:16, s. 2310-2323
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Tidskriftsartikel (refereegranskat)abstract
- In this work, a novel analytical method based on hollow fiber liquid phase microextraction (HF-LPME) and high performance liquid chromatography (HPLC) was developed for the analysis of melamine in fresh milk. The conditions of the HF-LPME were investigated and optimized. As a result, a supported liquid membrane containing 6-undecanone and di-2-ethylhexyl phosphoric acid (D2EHPA) was selected. The extractions were made from 25 mL aqueous donor phase (prepared from milk) with pH 5.0 to a more acidic acceptor phase (36 mu L 1 M HCl) and the mass transfer was driven by the proton gradient between these phases. Other optimum conditions of the HF-LPME were 60 min extraction time at 360 rpm stirring rate and an extraction factor of 21 times (extraction efficiency 3%) was obtained. The C8 column was operated at 1 mL/min at room temperature and the UV detection wavelength was 240 nm for HPLC. The mobile phase was 10 mM sodium n-octanesulfonate (pH 3.0) mixed with acetonitrile (85:15, v/v). The relative recovery of melamine for milk samples spiked with 0.5-25 mg/kg was in the range of 89.1-120.6% with the RSDs (n = 4) of 4.0-8.5%. It was found that the proposed method provided a linear range from 0.1 to 50 mg/kg (r(2) = 0.9993), method detection limit (MDL) of 0.003 mg/kg and method quantification limit (MQL) of 0.01 mg/kg. The obtained results demonstrated that HF-LPME combined with HPLC is a simple and cheap method for the determination of melamine in fresh milk.
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| 7. |
- Haghighi, Behzad, et al.
(författare)
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Fabrication and Characterization of a Thin-Layer Electrochemical Flow Cell and Its Application for Flow Analysis
- 2011
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Ingår i: Analytical Letters. - : Informa UK Limited. - 0003-2719 .- 1532-236X. ; 44:1-3, s. 258-270
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Tidskriftsartikel (refereegranskat)abstract
- The design and fabrication of a home-made thin-layer electrochemical flow cell are reported. The performance and electrochemical characteristics of thin-layer cells are evaluated in terms of flow rate and channel thickness. The adaptability of the flow cell for amperometric and electrochemiluminescence measurements is demonstrated. Also, a flow injection method comprising electrochemical generation followed by spectrophotometric detection is proposed for determination of bromide using the fabricated cell. The influence of chemical, electrochemical, and flow parameters on the absorbance and current signals are investigated, and under optimized conditions, the analytical features of the proposed method with respect to bromide detection are evaluated.
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| 8. |
- HALL, GF, et al.
(författare)
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AN ORGANIC-PHASE ENZYME ELECTRODE FOR CHOLESTEROL
- 1991
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Ingår i: Analytical Letters. - : Taylor andamp;amp; Francis. - 0003-2719 .- 1532-236X. ; 24:8, s. 1375-1388
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Tidskriftsartikel (refereegranskat)abstract
- An enzyme electrode is described for the determination of cholesterol dissolved in chloroform/hexane (1:1). The enzyme electrode is shown to be applicable to the determination of cholesterol in samples of butter and margarine.
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| 9. |
- Harborn, Ulrika, et al.
(författare)
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Determination of glucose in diluted blood with a thermal flow injection analysis biosensor
- 1994
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Ingår i: Analytical Letters. - : Informa UK Limited. - 0003-2719 .- 1532-236X. ; 27:14, s. 2639-2645
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Tidskriftsartikel (refereegranskat)abstract
- The glucose concentration in diluted whole blood has been measured, using a miniaturized thermal biosensor based on the enzyme thermistor principle. The biosensor is a small flow injection system. A sample volume of 20μl is injected into a flow of 50μ1/min. The heat produced when the sample passes the enzyme column is measured with a thermistor connected to a Wheatstone bridge. The enzyme column contains glucose oxidase and catalase co-immobilized on a solid support material. Samples of whole blood usually cause problems in flow-systems. The blood cells tend to block the enzyme column and the back pressure increases. We have tested a supeiporous agarose material as enzyme support material using tenfold diluted samples of whole human blood. The blood was collected from the finger-tip and diluted with buffer containing an anticoagulant and sodium fluoride. The number of samples possible to inject and the accuracy compared to the Boehringer Mannheim Reflolux have been determined. At least 100 ten-fold diluted blood samples could be injected on a micro-column of superporous agarose. The obtained glucose concentration correlated well with the one obtained with the reference instrument.
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| 10. |
- HU, J, et al.
(författare)
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AN ENZYME ELECTRODE FOR GLUCOSE CONSISTING OF GLUCOSE-OXIDASE IMMOBILIZED AT A BENZOQUINONE-MODIFIED CARBON ELECTRODE
- 1991
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Ingår i: Analytical Letters. - : Taylor andamp;amp; Francis. - 0003-2719 .- 1532-236X. ; 24:1, s. 15-24
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes an amperometric enzyme electrode for the analysis of glucose. The glucose sensor utilised adsorbed benzoquinone on a carbon electrode to mediate electron transfer from glucose oxidase. A linear response to 0-15 mM glucose was observed. The electrodes response to glucose, its pH profile and the effect of temperature are presented.
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| 11. |
- Islam, Farhana, et al.
(författare)
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Determination of n-Alkanes in Jet Fuel by Cold-electron Ionization Gas Chromatography-Mass Spectrometry
- 2017
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Ingår i: Analytical Letters. - : Informa UK Limited. - 0003-2719 .- 1532-236X. ; 50:10, s. 1593-1601
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Tidskriftsartikel (refereegranskat)abstract
- A rapid, easy, and reliable method was developed for the characterization of jet fuel with minimal sample preparation. A standard solution of 13 aliphatic n-alkanes in hexane was used to evaluate and validate the separation using cold-electron ionization gas chromatography-mass spectrometry. The method was evaluated and validated by the linearity, accuracy, and precision for all analytes. The limits of detection and quantification for each n-alkane were also evaluated. Nine major n-alkanes from n-octane to n-hexadecane were positively identified and quantified in jet fuel due to the enhanced molecular ion in the mass spectra. Major n-alkanes and their corresponding isomers in jet fuel were also identified from the extracted ion chromatograms. n-Undecane, n-dodecane, n-tridecane, and n-tetradecane were present at the highest concentrations in jet fuel at approximately 7% (v/v). The total concentrations of total straight chain alkanes were 34-37% in jet fuel that was comparable with the standard value of 32%.
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| 12. |
- Kempe, Maria, et al.
(författare)
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Binding studies on substrate- and enantio-selective molecularly imprinted polymers
- 1991
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Ingår i: Analytical Letters. - : Informa UK Limited. - 0003-2719 .- 1532-236X. ; 24:7, s. 1137-1145
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Tidskriftsartikel (refereegranskat)abstract
- A molecularly imprinted polymer was prepared using tert-butyloxycarbonyl-L-phenylalanine as the print molecule and methacrylic acid as the functional monomer. The bulk polymer obtained was ground, sieved, packed into a column and investigated in the HPLC-mode by frontal chromatography to determine the number of binding sites and dissociation constants for the enantiomers interacting with the polymer. The dissociation constant for the L-enantiomer of the print molecule was lower than for the D-enantiomer (6.3 mM and 8.1 mM, respectively). This means that the affinity for the L-enantiomer was higher than for the D-enantiomer. The number of binding sites in the polymer giving rise to these dissociation constants were determined to be 28 μmol per g dry polymer.
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| 13. |
- Nestor, Gustav, et al.
(författare)
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Nuclear Magnetic Resonance-Based Blood Metabolic Profiles of Rats Exposed to Short-Term Caloric Restriction
- 2015
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Ingår i: Analytical Letters. - : Informa UK Limited. - 0003-2719 .- 1532-236X. ; 48, s. 2613-2625
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Tidskriftsartikel (refereegranskat)abstract
- Caloric restriction increases the life-span of a number of organisms. The relationship between the increase in life-span and the extent of caloric restriction, however, varies among species. The underlying mechanisms are yet unknown, but appear to be related to changes in metabolism. In order to investigate the metabolic response of caloric restriction of rats, here is presented the first nuclear magnetic resonance (NMR) spectroscopy-based study of how blood metabolite profiles are influenced by graded levels of caloric restriction. The study involved three groups of obese rats exposed to 0, 20, and 40 percent caloric restriction for five days. Blood serum from each individual was analyzed by H-1 NMR and the resulting spectra were subjected to multivariate analysis by unsupervised principal component analysis and supervised orthogonal-partial least square discriminant analysis. The analyses revealed that a response to caloric restriction was present at 20 percent caloric restriction. The metabolites that distinguished the profiles at 20 percent restriction deviated from those at 40 percent restriction. The changes induced by caloric restriction were most clearly observed as an increased level of 3-hydroxybutyrate, and decreased levels of lipids and pyruvate. The metabolic responses of rats exposed to caloric restriction are in good agreement with a switch in metabolism from anabolic pathways towards fatty acid catabolism and gluconeogenesis, which is consistent with previous observations for mice.
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| 14. |
- Palchetti, I, et al.
(författare)
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Disposable screen-printed electrodes (SPE) mercury-free for lead detection
- 2000
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Ingår i: Analytical Letters. - : Taylor andamp;amp; Francis. - 0003-2719 .- 1532-236X. ; 33:7, s. 1231-1246
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Tidskriftsartikel (refereegranskat)abstract
- Strategies to modify screen-printed electrodes (SPE) for lead determination are reported. Dithizone was mixed with graphite ink to obtain a modified screen-printed strip to detect ppb levels of lead(II) (detection limit 12 mu g/l) using square wave anodic stripping voltammetry (SWASV). In addition, screen-printed electrodes were also modified by casting a few mu l of a Nafion(R) solution onto the working electrode surface. In this case, ppb levels of lead were detected (detection limit 15 mu g/l), using potentiometric stripping analysis (PSA). The addition of an ionophore to Nafion(R) polymer was also investigated, but this did not yield a significant improvement.
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| 15. |
- Rasinger, JD, et al.
(författare)
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Evaluation of an FIA operated amperometric bacterial biosensor, based on pseudomonas putida F1 for the detection of benzene, toluene, ethylbenzene, and xylenes (BTEX)
- 2005
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Ingår i: Analytical Letters. - : Taylor andamp;amp; Francis. - 0003-2719 .- 1532-236X. ; 38:10, s. 1531-1547
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Tidskriftsartikel (refereegranskat)abstract
- Recently, the development and optimization of a flow injection analysis (FIA) operated bacterial biosensor based on the aerobic catabolism of Pseudomonas putida ML2 was reported in the literature (Lanyon et al. 2004, 2005). By adapting information from these reports, we investigated whether operating parameters and procedures of the benzene biosensor could be directly applied to a new system based on a different bacterial strain for the detection of the whole benzene, toluene, ethylbenzene, and xylenes range. Cells of the investigated bacterial strain, Pseudomonas putida F1, were immobilized between two cellulose acetate membranes and fixed onto a Clark dissolved oxygen electrode. The P. putida F1 aerobically degrades benzene, toluene, and ethylbenzene (BTE) (Cho et al. 2000). The BTE biosensor in kinetic mode FIA displayed a linear range of 0.02-0.14 mM benzene (response time: 5 min, baseline recovery time: 15 min), 0.05-0.2 mM toluene (response time: 8 min, baseline recovery time: 20 min), and 0.1-0.2 mM ethylbenzene (response time: 12 min, baseline recovery time: 30 min), respectively. Due to the differences in sensitivity, response, and baseline recovery times for BTE, it was possible to differentiate each compound in mixtures of these volatile organic compounds (VOCs). No response for xylenes could be obtained since they cannot be completely metabolized by this bacterial strain. However, it was reported that the range of compounds degradable by P. putida F1 can possibly be expanded by cultivating the cells on different carbon sources (Choi et al. 2003). The sensor showed good intra- and interassay reproducibility, and all obtained results were comparable with those reported in the literature. The demonstrated reproducibility and the simplicity and ease of use as well as the portability for in situ measurements indicates that the biosensor could be suitable as a reliable initial warning device for elevated BTE levels in indoor and outdoor environments.
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| 16. |
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| 17. |
- Silva, Eugenia, et al.
(författare)
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Detection of polychlorinated biphenyls (PCBs) in milk using a disposable immunomagnetic electrochemical sensor
- 2007
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Ingår i: Analytical Letters. - : Taylor andamp;amp; Francis. - 0003-2719 .- 1532-236X. ; 40:7, s. 1371-1385
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Tidskriftsartikel (refereegranskat)abstract
- PCBs are among the most persistent and widely distributed pollutants in the global ecosystem and therefore it is of great importance for both human and environmental health to develop practical analytical systems to detect them. In this context, this work presents the application of an electrochemical immunosensor based on Screen-Printed Carbon-based Electrodes as transducers with antibody-coated magnetic microparticles as a solid phase. The immunoassay was based on direct competition between the analyte present in the samples and an alkaline phosphatase-labeled tracer. The product of the enzymatic reaction between AP and its substrate (alpha-naphthyl phosphate) was detected using differential pulse voltammetry. Sample extraction and clean-up was achieved using Solid Phase Extraction. Detection of low concentrations PCB was achieved and the method was shown to be applicable to both skimmed and whole milk. SPE was shown to improve the analysis.
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| 18. |
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| 19. |
- Winquist, Fredrik, et al.
(författare)
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A miniaturized voltammetric electronic tongue
- 2008
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Ingår i: Analytical Letters. - : Informa UK Limited. - 0003-2719 .- 1532-236X. ; 41:5, s. 917-924
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Tidskriftsartikel (refereegranskat)abstract
- A miniaturized electronic tongue based on pulsed voltammetry has been developed. It was made by inserting three types of wires acting as working electrodes (gold, platinum, and rhodium, diameter 0.25 mm) into a platinum tube acting as a counter electrode (diameter 2 mm, length 4 mm). The arrangement was connected to a potentiostat controlled by a computer. Due to the small size of the miniaturized electronic tongue, and since no reference electrode is used, the setup is very simple and convenient. In order to characterize the analytical possibilities of the miniaturized electronic tongue, some initial experiments were performed. These include the determination of trace amounts of cadmium and lead (in the µM range) in 5 µL samples. Furthermore, the setup was placed under the real tongue of a volunteer to follow saliva composition during exercise. Copyright © Taylor & Francis Group, LLC.
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| 20. |
- Xie, Bin, et al.
(författare)
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An integrated thermal biosensor array for multianalyte determination demonstrated with glucose, urea and penicillin
- 1996
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Ingår i: Analytical Letters. - : Informa UK Limited. - 0003-2719 .- 1532-236X. ; 29:11, s. 1921-1932
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Tidskriftsartikel (refereegranskat)abstract
- An integrated thermal biosensor array was designed and fabricated for the simultaneous determination of glucose, urea and penicillin. The sensor contains six thin-film thermistors which were fabricated on quartz chip by micromachining and semiconductor technology. This sensor allows the determination of three different analytes nearly simultaneously by serially partitioning a single microchannel into three distinct detection regions. Each of the regions contained one immobilized enzyme matrix and a pair of thermistors for differential measurement of temperature changes in association with the enzyme reactions. Using this device, glucose, urea and penicillin-G at different concentrations were determined in the mixed samples. Linear ranges of 1 to at least 25 mM urea and penicillin, and up to 20 mM glucose were obtained using a sample volume of 20 μL.
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| 21. |
- Xie, Bin, et al.
(författare)
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Hybrid biosensor for simultaneous electrochemical and thermometric detection
- 1997
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Ingår i: Analytical Letters. - : Informa UK Limited. - 0003-2719 .- 1532-236X. ; 30:12, s. 2141-2158
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Tidskriftsartikel (refereegranskat)abstract
- Simultaneous detection of multiple signals for common biochemical/electrochemical reactions is a challenging area of research for comparative studies. Based on our previous work with electrochemically assisted thermal biosensors, a hybrid biosensor has been developed for the simultaneous monitoring of the electrochemically generated current and the thermal signal produced in association with enzymatic catalysis. The sensor combined the two measurement principles of electrochemical regeneration of substrate and flow injection biocalorimetry. The enzyme column was constructed of a platinum foil in electrical contact with a poly (pyrrole)-coated reticulated vitreous carbon (RVC) matrix onto which tyrosinase was immobilized. The column functioned as enzyme reactor, working electrode and thermally sensitive element together with the thermistors. Catechol was oxidized by tyrosinase to form 1,2-benzoquinone which was subsequently regenerated electrochemically on the electrode surface. The primary heat production developed by the enzyme reaction could be measured calorimetrically. At the same time, the electrochemical reduction of 1,2-benzoquinone generated a current that was detected by the working electrode (enzyme column). Preliminary results showed good correlation of the two signals at both high and low oxygen concentrations in the buffer. A linear range between 12.5 and 250 μM catechol was obtained for the enzyme reaction. The sensitivity of the thermal measurement system was significantly enhanced by the recycling of catechol. The hybrid sensor provides a useful tool for comparative studies.
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| 22. |
- Zhang, Juankun, et al.
(författare)
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A Label Free Electrochemical Nanobiosensor Study
- 2009
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Ingår i: Analytical Letters. - : Taylor and Francis. - 0003-2719 .- 1532-236X. ; 42:17, s. 2905-2913
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Tidskriftsartikel (refereegranskat)abstract
- Nano-porous silicon (PS) is an attractive material for incorporation into biosensors, because it has a large surface area combined with the ability to generate both optical and electrical signals. In this paper, we describe a label-free nanobiosensor for bovine serum albumin (BSA). Nano-porous silicon produced in our laboratory was functionalized prior to immobilization of anti-BSA antibody on the surface. Reaction with BSA in phosphate buffered saline (PBS) buffer resulted in an impedance change which was inversely proportional to the concentration of the analyte. The system PBS buffer/antigen-antibody/PS constitutes an electrolyte-insulator-semiconductor (EIS) structure, thus furnishing an impedance EIS nanobiosensor. The linear range of the sensor was 0-0.27mgmL-1 and the sensitivity was less than 10 mu g mL-1.
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| 23. |
- Zhang, Juankun, et al.
(författare)
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LABEL-FREE ELECTROCHEMICAL DETECTION OF TETRACYCLINE BY AN APTAMER NANO-BIOSENSOR
- 2012
-
Ingår i: Analytical Letters. - : Taylor and Francis: STM, Behavioural Science and Public Health Titles / Taylor and Francis. - 0003-2719 .- 1532-236X. ; 45:9, s. 986-992
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Tidskriftsartikel (refereegranskat)abstract
- A novel aptamer nano-porous silicon (PS) biosensor was investigated for the rapid determination of tetracyclines. Electrochemical impedance spectroscopy (EIS) was used to analyze the behavior of the sensor. The specific binding of tetracycline to the aptamer biosensor led to a decrease in impedance. The corresponding impedance spectra (Nyquist plots) were obtained when serial concentrations of tetracycline were added into the system. An equivalent electrical circuit was used to fit the impedance data. The linear range of the sensor was 2.1-62.4 nM.
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| 24. |
- Zhang, Juankun, et al.
(författare)
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Nano-porous light-emitting silicon chip as a potential biosensor platform
- 2007
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Ingår i: Analytical Letters. - : Taylor andamp;amp; Francis. - 0003-2719 .- 1532-236X. ; 40:8, s. 1549-1555
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Tidskriftsartikel (refereegranskat)abstract
- Nano-porous silicon (PS) offers a potential platform for biosensors with benefits both in terms of light emission and the large functional surface area. A light emitting PS chip with a stable and functional surface was fabricated in our laboratory. When protein was deposited on it, the light emission was reduced in proportion to the protein concentration. Based on this property, we developed a rudimentary demonstration of a label-free sensor to detect bovine serum albumin (BSA). A serial concentration of BSA was applied to the light chip and the reduction in light emission was measured. The reduction of the light intensity was linearly related to the concentration of the BSA at concentrations below 10(-5) M. The detection limit was 8 x 10(-9) M.
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| 25. |
- Dicu, D, et al.
(författare)
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Indophenol and o-quinone derivaties immobilized on zirconium phosphate for NADH electro-oxidation
- 2003
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Ingår i: Analytical Letters. - 0003-2719. ; 36:9, s. 1755-1779
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Tidskriftsartikel (refereegranskat)abstract
- The electrocatalytic properties for NADH oxidation of five organic dyes, two indophenol derivatives (2,6-dichlorophenolindophenol and indophenol) and three o-quinone derivatives (phenanthrenequinone, pyrroloquinoline-quinone, and 1,2-naphthoquinone) were compared when adsorbed on zirconium phosphate entrapped in carbon paste. The electrochemical behavior of the immobilized dyes was investigated with cyclic voltammetry, performed in different aqueous buffers, at different potential scan rates and pH values. The electrocatalytic efficiency for NADH oxidation was evaluated from cyclic voltammetry, and the second order electrocatalytic rate constant was calculated from rotating disk electrode experiments, at various concentrations of NADH and pH values. These studies indicate that the mechanism of such electro-oxidation proceeds via the formation of an intermediate complex. A positive effect with the addition of Ca2+ cations to the solution was observed and the reaction rate for NADH oxidation increased. The highest second order rate constant was obtained for 2,6-dichlorophenolindophenol and found to be 4.6 × 106 M-1 s-1.
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