Microbial electrode sensor for vitamin B12

A microbial sensor consisting of immobilized Escherichia coli 215 and an oxygen electrode is described for the determination of vitamin B₁₂. When the sample solution is injected into the microbial electrode system, the increased consumption of oxygen by the micro-organisms causes a decrease in the dissolved oxygen around the porous membrane of the oxygen electrode and the current decreases gradually with time until a steady state is reached. The response time for a rate measurement is 2 h. When 0.5 mg of Escherichia coli 215 is immobilized, a linear relationship is obtained between the current decrease and the vitamin B₁₂ concentration between 5 × 10^?9 and 25 × 10^?9 g ml^?1.     

Enzymatic determination of cadmium,zinc, and lead in plant materials

Prospects are outlined for using the following enzymes (native and immobilized on polyurethane foam) in the rapid and highly sensitive determination of cadmium, zinc, and lead ions in plant materials (wild grass, fresh pea, and grape): horseradish peroxidase and alkaline phosphatases isolated from chicken intestine and Greenland seal small intestine. The analytical ranges of the above metals are 1 × 10^–3?25, 7 × 10^?3?250, and 3 × 10^?2?67 mg/kg dry matter, respectively. The enzymatic determination procedures developed are based on the inhibiting effect of metal ions on the catalytic activity of peroxidase in the oxidation of o-dianisidine with hydrogen peroxide and alkaline phosphatases in the hydrolysis of p-nitrophenyl phosphate. The rates of enzymatic reactions were monitored spectrophotometrically or visually. In the analysis of plant extracts, their high acidity was diminished by choosing optimum dilution factors and pH values for test samples and the nature and concentration of a buffer solution. The interference of iron(III) was removed by introducing a 0.1 M tartaric acid solution into the indicator reaction. The accuracy of the results of the enzymatic determination of cadmium, zinc, and lead in plant materials was supported by atomic absorption spectrometry and anodic stripping voltammetry.     

An amperometric monoamine oxidase biosensor for determining some antidepressants

An amperometric biosensor based on a platinum screen-printed electrode and immobilized monoamine oxidase is developed to determine antidepressants of different classes. Petylyl, pyrazidol, and flu-oxetine can be determined with determination limits of 8 × 10^?9, 8 × 10^?7, and 8 × 10^?10 M, respectively. A procedure is proposed for determining fluoxetine in tablets. It is shown that petylyl can be selectively determined by an immunochemical technique using the developed biosensor and immobilized antibodies in the concentration range from 1 × 10^?4 to 1 × 10^?8 M.     

A Novel Optical Sensor for Determination of Thiocyanate

Abstract

A novel optical sensor (optode) is described for the determination of thiocyanate using methyltrioctylammonium chloride immobilized on triacetylcellulose membrane. The response to thiocyanate is the result of adsorption of [Co(SCN)₄]^2? on sensing membrane, which caused the colorless membrane to change to blue. This optode can readily be regenerated by using 0.02 mol/l sodium oxalate solution. The linear range of the method was 3.44×10^?5 to 8.61×10^?4 mol/l of thiocyanate with a limit of detection 1.51×10^?5 mol/l. The relative standard deviation for eight replicate measurements of 8.61×10^?5 and 4.30×10^?4 mol/l of thiocyanate was 3.45 and 1.23%, respectively. The sensor was successfully applied for the determination of thiocyanate in saliva of smokers, nonsmokers and various water samples.     

A Novel Fiber Optic Biosensor for the Determination of Adrenaline Based on Immobilized Laccase Catalysis

Abstract

A novel fiber optic biosensor for the determination of adrenaline based on immobilized laccase catalysis and fluorescence quenching was designed and fabricated. The immobilized laccase formed by the immobilization of laccase on the CuTAPc-Fe₃O₄ nanoparticles composite were used to catalyze the oxidation of adrenaline and the fluorescent oxygen-sensing membrane was used to detect the consumption of oxygen. The effects of pH and temperature on laccase activity using adrenaline as the substrate were studied. The optimal pH and temperature for the activity of immobilized laccase are 5.0 and 55°C, respectively. The immobilized laccase has good thermal, storage and operation stability. The lock-in technology was used to detect the change of the life time of the oxygen-sensing membrane. By using ABTS as the electron mediator, the biosensor showed a response time of 30 sec. The biosensor has good performance in the adrenaline concentration ranges of 2.0 × 10^?7 to 9.0 × 10^?7 mol/l and 1.0 × 10^?8 to 9.0 × 10^?8 mol/l, and it also shows good stability.     

Flow-injection determination of d-mannitol with immobilized mannitol dehydrogenase

A flow-injection system is described for the determination of d-mannitol. Mannitol dehydrogenase is immobilized on poly(vinyl alcohol) beads and packed in a column (5 cm × 4 mm i.d.). The NADH formed is detected fluorimetrically. The response is linear between 5 × 10^?7 and 1 × 10^?4 M mannitol and the detection limit is 1 × 10^?7 M. The throughput is 30 samples per hour. The reactor is stable for at least 8 weeks.     

Flow-injection spectrophotometric determination of acetyl-coenzyme A with immobilized phosphotransacetylase

Phosphotransacetylase (PTA) is immobilized on AF-Tresyl TOYOPEARL 650 gel and used on-line in a stainless-steel column (10 × 4 mm i.d.). CoA-SH liberated enzymatically from acetyl-CoA is reacted with Ellman's reagent [5,5′-dithiobis(2-nitrobenzoic acid)] in the carrier stream. The calibration graph for acetyl-CoA is linear from 4 × 10^?6 to 4 × 10^?4 M and the detection limits is 8 × 10^?7 M. The immobilized enzyme can be employed for over 4 months without any significant decrease in activity. The enzyme retains its activity in methanol even though the initial rate of reaction is decreased.     

Adsorptive stripping voltammetry of nickel at a bare glassy carbon electrode

A bare glassy carbon electrode is applied to nickel determination by adsorptive stripping voltammetry in the presence of dimethylglyoxime as a complexing agent. A procedure of nickel determination and electrode regeneration was proposed. The calibration graph for Ni(II) for an accumulation time of 120?s was linear from 2?×?10^?9 to 1?×?10^?7?mol?L^?1. The detection limit was 8.2?×?10^?10?mol?L^?1. The relative standard deviation for a solution containing 2?×?10^?8?mol?L^?1 of Ni(II) was 4.1%. The proposed procedure was applied for Ni(II) determination in certified water reference materials.     

Flow-injection determination of malate with immobilized malate dehydrogenase

Malate dehydrogenase (MDH) is immobilized chemically on controlled-pore glass and used on-line in a glass minicolumn (25×2.5 mm i.d.). Malate solution passes through the minicolumn of immobilized MDH and the NADH formed is monitored spectrophotometrically from 9 × 10-^?4 down to 7 × 10^?6 M (36 ng in 40 μl) at 50 samples h^?1.     

Bioluminescent assays with immobilized firefly luciferase based on flow injection analysis

A flow-injection manifold incorporating immobilized firefly luciferase is described. The detector design and reaction conditions are discussed and results are presented for the determination of adenosine-5′-triphosphate over the range 1 × 10^?12?1 × 10^?5 M. Modifications for creatine phoshokinase (10–400 U l^?1) and creatine phosphate (10^?t–10^?1 M), both determined indirectly via ATP, are also described.     

A Nitric Oxide Biosensor Based on Myoglobin Adsorbed on Multi‐Walled Carbon Nanotubes

Myoglobin (Myb) of horse heart is incorporated on multi‐walled carbon nanotubes (MWNTs) and immobilized at a glassy carbon (GC) electrode surface. Its electrochemical behavior and enzyme activity are characterized by employing electrochemical methods. The results indicate that MWNTs can obviously promote the direct electron transfer between Myb and electrode, and that the Myb on MWNTs behaves as an enzyme‐like activity towards the electrochemical reduction of nitric oxide (NO). Accordingly, an unmediated NO biosensor is constructed. Experimental results reveal that the peak current related to NO is linearly proportional to its concentration in the range of 2.0×10^?7–4.0×10^?5 mol/L. The detection limit is estimated to be 8.0×10^?8 mol/L. Considering a relative standard deviation of 2.1% in seven independent determinations of 1.0×10^?5 mol/L NO, this biosensor shows a good reproducibility. The biosensor based on Myb/MWNTs modified electrode can be used for the rapid determination of trace NO in aqueous solution with a good stability, nice selectivity and easy construction.     

Direct Determination of Trace Dopamine in an Ascorbic Acid Solution at a Bare Glassy Carbon Electrode Using Differential Pulse Voltammetry

It is difficult to monitor dopamine (DA) accurately with a bare glassy carbon electrode because of the interference of ascorbic acid (AA). In this paper, a method for the determination of DA in an AA solution using differential pulse voltammetry was established. Because AA loses its electrochemical activity after being oxidized, hydrogen peroxide was used to oxidize AA, and the interference of AA was completely eliminated. As a result, trace DA could be directly determined in the AA solution with a bare glassy carbon electrode. When trace DA was determined in a 1.0 mmol L^?1 AA solution, there was a wide linear range from 3.0×10^?8 mol L^?1 to 1.0×10^?5 mol L^?1. The application of this method was demonstrated by the selective measurement of DA in an injection without pretreatment.     

Direct Electrochemistry and Electrocatalysis of Hemoglobin Based on Nafion‐Room Temperature Ionic Liquids‐Multiwalled Carbon Nanotubes Composite Film

A robust and effective composite film combined the benefits of Nafion, room temperature ionic liquid (RTIL) and multi‐wall carbon nanotubes (MWNTs) was prepared. Hemoglobin (Hb) was successfully immobilized on glassy carbon electrode surface by entrapping in the composite film. Direct electrochemistry and electrocatalysis of immobilized Hb were investigated in detail. A pair of well‐defined and quasi‐reversible redox peaks of Hb was obtained in 0.10 mol·L^?1 pH 7.0 phosphate buffer solution (PBS), indicating that the Nafion‐RTIL‐MWNTs film showed an obvious promotion for the direct electron transfer between Hb and the underlying electrode. The immobilized Hb exhibited an excellent electrocatalytic activity towards the reduction of H₂O₂. The catalysis current was linear to H₂O₂ concentration in the range of 2.0×10^?6 to 2.5×10^?4 mol·L^?1, with a detection limit of 8.0×10^?7 mol·L^?1 (S/N=3). The apparent Michaelis‐Menten constant (K_m^app) was calculated to be 0.34 mmol·L^?1. Moreover, the modified electrode displayed a good stability and reproducibility. Based on the composite film, a third‐generation reagentless biosensor could be constructed for the determination of H₂O₂.     

Flow-injection determination of l-ascorbate with cucumber juice as carrier

Cucumber (Cucumis sativus L.) juice has a high l-ascorbate oxidase activity and can be used as the carrier solution in an amperometric flow-injection system for the determination of l-ascorbate. The determination time is 1 min. The calibration graph is linear over the range 5×10^?4–7×10^?3 M (RSD 4%). No enzyme purification is needed. The juice solution retains its activity for 8 days with recycling.     

Flow-coulometric detector for uric acid in human urine

A novel flow-coulometric detector integrating an immobilized uricase reactor and an electrolytic cell was fabricated and used for the determination of uric acid in human urine. The procedure is based on the measurement of the total charge with and without passing the sample through an enzyme reactor which allows the complete conversion of the electro-active uric acid in electro-inactive products. The amount of uric acid is linearly related to the difference between the two total charges. The current efficiencies for 1 × 10^?4-1 × 10^?3 M uric acid were found to be nearly 100% (r.s.d. < 1%).     

Catalytic Adsorptive Stripping Voltammetry of Cobalt in the Presence of Dimethylglyoxime and Nitrite at In Situ Plated Lead–Copper Film Electrode

A lead‐copper film electrode was proposed for Co(II) determination by catalytic adsorptive stripping voltammetry. The electrode was plated in situ and hence the exchange of a solution after plating step was not required. At optimized conditions the calibration graph for Co(II) was linear from 5×10^?10 to 2×10^?8 mol L^?1 for accumulation time of 15 s. The relative standard deviation for Co(II) determination at concentration 5×10^?9 mol L^?1 was 4.1%. The detection limits for Co(II) were 1.2×10^?10 and 1.0×10^?11 mol L^?1 for an accumulation time of 15 and 180 s, respectively. The method was applied to Co(II) determination in certified reference material and other water samples.     

Determination of Zinc(II) ions with a reactor containing immobilized carboxypeptidase a in a flow system

Zinc(II) was determined in the range 2–20 × 10^?7 M through its activation of immobilized, metal-free carboxypeptidase A. The activity was assessed by injection of hippuryl-l-phenylalanine and the decomposition product was determined by high-performance liquid chromatography. Cadmium(II) and mercury(II) depressed the zinc response of the method although there was excess of metal-free enzyme in the reactor. Regeneration was made by pumping a 1,10-phenathroline solution through the reactor between successive samples.     

Synthesis and Characterization of Copper-Doped Zinc Selenide Quantum Dots as Fluorescence Probes for Sparfloxacin

Copper-doped zinc selenide quantum dots modified with mercaptopropionic acid were prepared. The fluorescence quenching of the quantum dots was directly proportional to sparfloxacin concentration. A novel method was established to determine sparfloxacin using the copper-doped zinc selenide quantum dots as fluorescent probes. The interaction between the quantum dots and sparfloxacin was investigated by fluorescence and absorption spectroscopies. A linear relationship was obtained between the quenched fluorescence and sparfloxacin concentration from 1 × 10^?6 to 1.8 × 10^?5 moles per liter in KH₂PO₄-Na₂HPO₄ buffer at pH 7.5 using copper-doped zinc selenide quantum dots at 2.9 × 10^?6 moles per liter. The limit of detection for sparfloxacin was 2.4 × 10^?9 moles per liter. The method was used for the determination of sparfloxacin in tablets and water with satisfactory results.     

Flow-injection chemiluminescence determinations for human blood lead using controlled reagent release technology

A flow-through CL method for the determination of lead combined with controlled-reagent-release technology has been developed. Chemiluminescence (CL) reagents luminol and potassium permanganate were immobilized on anion exchange resin by electrostatic interaction. Lead ion was determined by its enhancing effect on the CL reaction between luminol and potassium permanganate. Both luminol and potassium permanganate were eluted from the anion exchange resin column by sodium phosphate solution. The linear range of the system was 10 μg mL^?1, and the detection limit was 5?×?10^–9 g mL^?1 lead (3σ). A complete analysis could be performed in 1 min with a relative SD 3.2% (1.0?×?10^–7 g mL^?1, n?=?9). The column shows remarkable stability and can be reused over 350 times and 21 days. The method has been applied to determine lead in human blood samples.     

Carbon Composite Electrode Modified with Copper(II) Phosphate Immobilized in a Polyester Resin for Voltammetric Determination of Catechin in Teas

A carbon composite electrode modified with copper (II) phosphate immobilized in a polyester resin (Cu₃(PO₄)₂-Poly) was proposed for the voltammetric determination of catechin in teas. The modified electrode allows the determination of catechin (CAT) at lower potential than that observed at an unmodified electrode. Several parameters that can influence the voltammetric response of the proposed electrode such as carbon composite composition, pH of electrolyte, and others were investigated. The peak current was proportional to the concentration of catechin in the range from 9.9 × 10^?8 to 1.2 × 10^?6 mol L^?1, with a detection limit of 5.8 × 10^?8 mol L^?1. The stability and repeatability of the electrode for the determination of catechin were discussed, and the modified electrode was applied with success in the determination of catechin in teas.