Competitive amperometric morphine sensor based on an agarose immobilised molecularly imprinted polymer

A morphine-sensitive device was constructed based on a molecularly imprinted polymer. The imprinted polymer exhibited recognition properties previously. A method of detection based on competitive binding was used to measure morphine in the concentration range 0.1–10 μg/ml. A morphine concentration of 0.5 μg/ml gave a peak current (by oxidation) of 4 nA. The method of morphine detection involves two steps. In the first step, morphine binds selectively to the molecularly imprinted polymer in the sensor. In the second step, an electroinactive competitor (codeine) is added in excess, whence some of the bound morphine is released. The released morphine is detected by an amperometric method. The advantages of this type of sensor compared to biosensors based on antibodies, enzymes or cells are discussed. This sensor, based on an artificial recognition system, demonstrates autoclave compatibility, long-time stability and resistance to harsh chemical environments.     

Amperometric sensor for ethanol based on one-step electropolymerization of thionine-carbon nanofiber nanocomposite containing alcohol oxidase

Thionine had strong interaction with carbon nanofiber (CNF) and was used in the non-covalent functionalization of carbon nanofiber for the preparation of stable thionine-CNF nanocomposite with good dispersion. With a simple one-step electrochemical polymerization of thionine-CNF nanocomposite and alcohol oxidase (AOD), a stable poly(thionine)-CNF/AOD biocomposite film was formed on electrode surface. Based on the excellent catalytic activity of the biocomposite film toward reduction of dissolved oxygen, a sensitive ethanol biosensor was proposed. The ethanol biosensor could monitor ethanol ranging from 2.0 to 252 μM with a detection limit of 1.7 μM. It displayed a rapid response, an expanded linear response range as well as excellent reproducibility and stability. The combination of catalytic activity of CNF and the promising feature of the biocomposite with one-step non-manual technique favored the sensitive determination of ethanol with improved analytical capabilities.     

Amperometric sensor based on the alkaline phosphatase activity

The construction and response of an immobilized enzyme electrode as an amperometric sensor are described. Alkaline phosphatase was covalently bonded to a nylon filter mesh using glutaraldehyde and bovine serum albumin (BSA) as crosslinkers. This modified membrane was then attached to the surface of a glassy-carbon (GC) electrode. Substrate mass transport and enzymatic catalysis control were investigated in a rotating disk electrode. Various response characteristics and kinetic parameters were evaluated and are compared to those of a previously reported amperometric alkaline phosphatase electrode.     

Ammonium ion sensor based on immobilized nitrifying bacteria and a cation-exchange membrane

The ammonium ion sensor is based on nitrifying bacteria isolated from activated sludge. The sensor comprises a cation-exchange membrane, an alkaline solution layer (pH 10), a gas-permeable membrane, an immobilized microbial membrane, and an oxygen electrode. This novel combination provides accurate amperometric determinations of ammonium ions in aqueous solutions within 7 min in the range 10^-4– 4.5 × 10^-2 M. Volatile amines or other ions do not interfere. The relative error is within 4% and the sensor can be used continually for more than 10 days.     

Alcohol-FET sensor based on a complex cell membrane enzyme system

An alcohol -FET sensor was developed by use of a complex enzyme system in a cell membrane and an ion-sensitive field effect transistor (ISFET). The cell membrane of Gluconobacter suboxydans IFO 12528, which converts ethanol to acetic acid, was immobilized on the gate of an ISFET with calcium alginate gel coated with nitrocellulose. This ISFET (1), a reference ISFET without the cell membrane (ISFET 2) and an Ag/AgCl reference electrode were placed in 5 mM Trismalate buffer (pH 5.5, 25°C), and the differential output between ISFETS 1 and 2 was measured. The output of the sensor was stabilized by adding pyrroloquinoline quinone. The response time was ca. 10 min., and there was a linear relationship between the differential output voltage and the ethanol concentration up to 20 mg l^?1. The output of the sensor was stable for 40 h below 30°C. The sensor responded to ethanol, propan- 1-ol and butan- 1-ol, but not to methanol, propan-2-ol and butan-2-ol. The sensor was used to determine blood ethanol.     

Initial studies of an immobilised, regenerable chemiluminescent sensor

The first reported use of a regenerable chemiluminescent polymer for chemical analysis is described. Ruthenium tris(4-methyl-4′-vinyl-2,2′-bipyridine) was electropolymerised onto the surface of a Pt electrode. This system was optimised for detection of oxalate by investigating the effect of both scan rate and the pH of the analyte solution. A chemically modified electrode successfully completed over 200 regeneration cycles over a 6-month period, demonstrating the stability of the system. A range of other species has also been tested for activity with the chemiluminescent polymer. The system functions in a similar way to traditional homogeneous chemiluminescent methods, but the active compound is retained and re-used rather than discarded. This results in both environmental and cost savings.     

Development of an optical fibre Al(III) sensor based on immobilised chrome azurol S

Chrome azurol S immobilised on XAD-2 has been used in this study as a reagent phase for the development of an optical fibre Al(III) sensor. Using a kinetic approach, this sensor was able to give a linear response in the Al(III) concentration range of 1.3 x 10(-5)-2.0 x 10(-4) M with a limit of detection of 1.0 x 10(-4) M. The optimum responses were obtained at pH 6.0 and when the solution was stirred. The sensor response was found to have a repeatability and reproducibility of 1.6% and 5.8%, respectively. The results obtained for Al(III) determination in aqueous sample were in good agreement with those obtained using graphite furnace-atomic absorption spectrometry.     

Development of an optical fibre reflectance sensor for p-aminophenol detection based on immobilised bis-8-hydroxyquinoline

2,2′-(1,4-Phenylenedivinylene)bis-8-hydroxyquinoline (PBHQ), a highly sensitive reagent used for the colorimetric determination of p-aminophenol (PAP), was successfully immobilised on XAD-7 and coupled with optical fibres to investigate a sensor-based approach for determining p-aminophenol. The solid-state sensor is based on the reaction of PAP with PBHQ in presence of an oxidant to produce an indophenol dye. The reflectance measurements were carried out at a wavelength of 647 nm since it yielded the largest divergence different in reflectance spectra before and after reaction with the analyte. The linear dynamic range of PAP was found within the concentration range of 0.1-2.18 mg l⁻¹ with its LOD of 0.02 mg l⁻¹. The sensor response from different probes (n = 7) gave a R.S.D. of 4.4% at 1.09 mg l⁻¹ PAP concentration. The response time of the optical one-shot sensor was 5 min for a stable solution. As this PAP sensor is irreversible, a fresh sensor has to be used for each measurement. All the experimental parameters were optimized for the determination of PAP. Using the optical sensing probe, PAP in pharmaceutical wastewater and paracetamol was determined. The effect of potential interferences such as inorganic and organic compounds was also evaluated. Potential on-site determination of PAP with such sensors can indirectly aid detection of organo-phosphorus nerve agents and pesticides in the field by inhibition of acetylcholine esterase-catalyzed hydrolysis of p-aminophenyl acetate to p-aminophenol.     

Amperometric enzyme sensor for glucose based on graphite paste-modified electrodes

Amperometric enzyme electrode for glucose is described based on the incorporation of glucose oxidase (GOD) into graphite paste modified with tetracyanoquinodimethane (TCNQ). The incorporated enzyme exhibits high activity and long-term stability over the earlier TCNQ-based glucose sensor (1). The sensor provides a linear response to glucose over a wide concentration range. The response time of the sensor is 15-50 sec, and the detection limit is 0.5 mM. Stable response to the substrate was obtained during a period of 35 d. Application of the sensor in the plasma analysis is reported.     

Enzyme electrode for glucose based on an iodide membrane sensor

The construction of a new type of enzyme electrode for the potentiometric determination of glucose is reported. The electrode response is based on the enzymecatalyzed reactions: The highly selective iodide sensor monitors the local decrease in the iodide activity at the electrode surface. The properties of the above reactions were examined kinetically, with flow-stream techniques and potentiometric detection. The glucose electrode constructed and the use of flow-stream experiments with two iodide sensors provided accurate and convenient glucose determinations in the absence of some oxidizing and reducing agents.     

Amperometric methylene blue-mediated sensor highly sensitive to hydrogen peroxide based on a composite membrane of regenerated silk fibroin and poly-vinyl alcohol as immobilization matrix for horseradish peroxidase

Horseradish peroxidase (HRP) was effectively entrapped in a novel composite membrane of poly-vinyl alcohol and regenerated silk fibroin, and IR was employed to provide a useful insight into the structure of the composite membrane. A methylene bluemediated sensor highly sensitive to hydrogen peroxide was constructed, which was based on the immobilization of HRP in the composite membrane. Cyclic voltammetry and amperometric measurement were utilized to demonstrate the feasibility of electron communication between immobilized HRP and a glassy carbon electrode in the bioelectrocatalytic reduction of hydrogen peroxide via methylene blue. Performance and characteristics of the sensor were evaluated with regard to response time, detection limit, selectivity, and dependence on temperature and pH as well as operating and storage stability. The sensor possesses a variety of characteristics including high sensitivity, rapid response time and a low detection limit of 0.1 μmol/L.     

Amperometric methylene blue-mediated sensor highly sensitive to hydrogen peroxide based on a composite membrane of regenerated silk fibroin and poly-vinyl alcohol as immobilization matrix for horseradish peroxidase

 Horseradish peroxidase (HRP) was effectively entrapped in a novel composite membrane of poly-vinyl alcohol and regenerated silk fibroin, and IR was employed to provide a useful insight into the structure of the composite membrane. A methylene blue-mediated sensor highly sensitive to hydrogen peroxide was constructed, which was based on the immobilization of HRP in the composite membrane. Cyclic voltammetry and amperometric measurement were utilized to demonstrate the feasibility of electron communication between immobilized HRP and a glassy carbon electrode in the bioelectrocatalytic reduction of hydrogen peroxide via methylene blue. Performance and characteristics of the sensor were evaluated with regard to response time, detection limit, selectivity, and dependence on temperature and pH as well as operating and storage stability. The sensor possesses a variety of characteristics including high sensitivity, rapid response time and a low detection limit of 0.1 μmol/L. Received: 10 January 1996/Revised: 20 March 1996/Accepted: 25 March 1996     

Serine-selective membrane probe based on immobilized anaerobic bacteria and a potentiometric ammonia gas sensor

A new class of bioselective membrane probes using anaerobic bacteria is introduced with the successful construction of a L-serine-selective probe consisting of Clostridium acidiurici cells coupled to a potentiometric ammonia gas sensor. The intact cells containing the enzyme serine dehydratase are physically immobilized at the electrode surface in conjunction with iron(II) stearate, which is shown to enhance response characteristics. The potential vs. log concentration plot is linear from 1.6 × 10^-2 to 1.8 × 10^-4M serine with an average slope of 54 mV/decade and response times of 3–5 min. Optimal behavior of the probe is retained even in non-deaerated media for at least three days, and significant interference is posed only by L-glutamine. Quantitative conversion of serine is demonstrated over the linear concentration range, suggesting possible analytical or clinical applications for these probes utilizing anaerobic bacteria     

Alcohol sensor based on membrane-bound alcohol dehydrogenase

Ethanol is determined by a sensor system using purified, immobilized mernbrane-bound alcohol dehydrogenase frorn Gluconobacter suboxydans, attached to a platinum disk electrode (3 mm diameter), and covered with a dialysis membrane. Hexacyanoferrate (III) is used as the redox acceptor. To correct for the influence of interfering substances, this alcohol sensor is compensated by a control electrode which has no immobilized enzyme. The potential of these platinum electrodes was set at + 350 mV vs. Ag/AgCl. Linearity was observed in the range 0.1–5 mM ethanol, the response time was less than 5 min, the maximum sensitivity was obtained at 45°C and the optimum pH was in the range 4.5–5.5. The sensitivity decreased to 80% of the initial value after 1 month at 30°C. When the alcohol sensor system was applied to the determination of ethanol in alcoholic beverages, a good correlation was obtained between the results and those obtained by gas chromatography.     

Amperometric sensor for hydrogen peroxide based on poly(aniline-co-p-aminophenol)

It was found that the poly(aniline-co-p-aminophenol) film can effectively catalyze the oxidation of hydrogen peroxide in a sodium citrate buffer solution with pH 5.0. Here, we applied the copolymer to the construction of an efficient electrochemical sensor to determine the concentration of hydrogen peroxide. The sensor exhibited an excellent electrocatalytic activity toward the oxidation of H₂O₂, and the interferences of ascorbic acid and phenol were completely avoided. Unlike the inherent instability of enzyme, the poly(aniline-co-p-aminophenol) film-based sensor showed an outstanding stability.     

Amperometric sulfite sensor based on multiwalled carbon nanotubes/ferrocene-branched chitosan composites

A novel amperometric sensor for the determination of sulfite was fabricated based on multiwalled carbon nanotubes (MWCNTs)/ferrocene-branched chitosan (CHIT-Fc) composites-covered glassy carbon electrode (GCE). The electrochemical behavior of the sensor was investigated in detail by cyclic voltammetry. The apparent surface electron transfer rate constant (K_s) and charge transfer coefficient (α) of the CHIT-Fc/MWCNTs/GCE were also determined by cyclic voltammetry, which were about 1.93 cm s⁻¹ and 0.42, respectively. The sensor displayed good electrocatalytic activity towards the oxidation of sulfite. The peak potential for the oxidation of sulfite was lowered by at least 330 mV compared with that obtained at CHIT/MWCNTs/GCE. In optimal conditions, linear range spans the concentration of sulfite from 5 μM to 1.5 mM and the detection limit was 2.8 μM at a signal-to-noise ratio of 3. The proposed method was used for the determination of sulfite in boiler water. In addition, the sensor has good stability and reproducibility.     

Lead-selective membrane potentiometric sensor based on an 18-membered thiacrown derivative.

A PVC-based membrane electrode for lead ions based on hexathia-18-crown-6-tetraone as membrane carrier was prepared. The influence of membrane composition, pH of test solution and foreign ions on the electrode performance were investigated. The electrode showed a Nernstian response over a lead concentration range from 1.0 x 10(-6) to 8.0 x 10(-3) M at 25 degrees C, and was found to be very selective, precise and usable within the pH range 3.0-6.0. The electrode was successfully used as an indicator electrode in potentiometric titration of lead ions and in direct determination of lead in water samples.     

A methane gas sensor based on oxidizing bacteria

A bacterial sensor system based on Methylomonas flagellata AJ 3670 is described for methane determinations. The system consists of a bacterial, reactor, a reference reactor and two oxygen sensors. The current decreases with time until a steady state is reached within 30 s at 30°C; the maximum current difference is obtained at 30°C and pH 7.2. The response time for the determination of methane is less than 1 min. A linear relationship is obtained between the current difference and the methane concentration below 6.6 mM; the lower limit of determination is 5 μM, and the current decrease is reproducible within 5%. The current output of the sensor is almost stable for more than 10 days and 250 assays.     

Amperometric sensor for nitrite based on copper tetrasulphonated phthalocyanine immobilized with poly-L-lysine film

In this work, an amperometric sensor for nitrite detection based on a glassy carbon electrode modified with copper tetrasulphonated phthalocyanine immobilized by polycationic poly-L-lysine film is presented. The modified electrode showed an excellent catalytic activity toward nitrite oxidation. A linear response range from 0.12 up to 12.20 micromol L(-1) was obtained with a sensitivity of 0.83 microA L micromol(-1). The detection limit for nitrite was 36 nmol L(-1). The repeatability of the proposed sensor, evaluated in terms of relative standard deviation, was 1% for 10 measurements of 10 micromol L(-1) nitrite solution. Finally, the developed sensor was applied for nitrite determination in water samples and the results were in agreement to the comparative method. The average recovery for the samples was 101 (+/-4)%.     

Amperometric sensor for hypoxanthine and xanthine based on the detection of uric acid

The construction and response of an immobilized enzyme modified electrode as an amperometric sensor is described. Xanthine oxidase was adsorbed on a carbon paste electrode and physically entrapped with a semipermeable membrane. Uric acid, the product of the enzymatic reaction, was oxidized electrochemically at +0.4 V vs. Ag/AgCl, yielding a steady-state current directly related to the bulk concentration of the substrate. Hypoxanthine and xanthine were determined in the range 5–100 μM at Ph 7.2 with good precision. Interferences are discussed.