Double Matrix Membrane Research Articles

Potentiometric biosensor for urea determination in milk

A potentiometric urea sensitive biosensor, using a NH 4 + ion sensitive electrode in double matrix membrane (DMM) technology as the transducer, has been described. Thick film screen printing technique was utilized for the fabrication of the basal conducting track of the potentiometric electrode and also for the development of Ag/AgCl reference electrode. The ion sensitive polymer matrix membrane could be formed in the presence of an electrochemically inert filter paper. The electrochemical response behavior of the NH 4 + ion sensitive electrode has been studied initially. Later, a urea biosensor has been developed by immobilizing the urease enzyme, through entrapping, onto the ion sensitive membrane using a polymer matrix of poly(carbamoylsulphonate) (PCS) and polyethyleneimine (PEI). The urea biosensor responded rapidly and in a stable manner to the changes in the test urea concentrations. The sensor exhibited a detection limit of 2.5 × 10 −5 mol/L. The average slope in the linear range has been found to be 51.7 ± 0.5 mV/decade. The biosensor system has, then, been tested for the detection of urea levels in the real samples of milk. A good agreement could be observed between the urea concentrations detected by the developed biosensor and the spectrophotometric technique.

Application of Double Matrix Membrane Technology for Ion-Selective Electrodes

Double matrix membrane technology (DMM) is an excellent technique for creating inexpensive and robust electrochemical electrodes. In this report the use of DMM-electrodes to measure different ions (namely Ca2+, Mg2+, Cl−) is described. The ion-selective membranes are basing on PVC and stabilized by deposition on a porous matrix. The authors determined the following characteristics of the ion-selective electrodes (ISEs): sensitivity; detection limit; linear range and selectivity coefficients. When changing the analyte concentration response time was lower than 30 s (Ca2+, Cl−) or 1 min (Mg2+). In the case of the determination of the selectivity coefficients it was considered in which concentrations the interfering ions naturally occur in physiological matrices, e.g., blood. In case of the chloride-selective electrode the discrimination of ascorbic acid and salicylate was investigated. The coefficients were evaluated by using the fixed interference method (FIM). The reproducibility of electrochemical characteristic was determined by investigating 120 mass-produced ammonium-selective electrodes. Furthermore, it was discovered that DMM-based potassium-selective electrodes may be stored stable for at least 4.5 years.

Densitometric analysis for quality control in poly(vinyl chloride)-membrane electrode manufacturing

This paper describes a simple densitometric method which will enable high quality potentiometric ion-selective electrodes (ISEs) to be produced. When assembling double matrix membrane (DMM) technology electrodes, it is critical that the membrane is located for the electrode to function properly. It is, therefore, important that this is monitored during the production process. The membrane must be able to come into contact with the relevant substance to be analysed but it is also important that there is no leakage between the solution and the sensor conductor path. The poly(vinyl chloride)- (PVC) membrane material is inserted into sensor configuration. All manufactured sensors need to be checked so that there is no leakage in the membrane. After the PVC is inserted, it is necessary to perform a densitometric measurement to check that the correct amount of PVC is presented and that it is evenly distributed. A pigment is added to the PVC to enable this to occur. The pigment ensures that part of the light spectrum emitted by the densitometer is absorbed. The reflected light is then analysed to identify both the quantity and location of the PVC. We found that adding a pigment to the PVC-membrane surrounding ammonium-selective electrodes does not change the electrodes electrochemical characteristics.

Disposable potentiometric enzyme sensor for direct determination of organophosphorus insecticides.

A potentiometric disposable enzyme sensor for the direct and fast determination of organophosphorus (OP) insecticides was developed by using an organophosphorus hydrolase (OPH) immobilized on an ion-selective electrode. The disposable screen-printed transducer was based on double matrix membrane technology which allows easy mass production. The potentiometric device consisted of a H(+)-sensitive electrode with integrated Ag/AgCl reference electrode. The electrodes were prepared with N,N-dioctadecylmethylamine as H(+)-sensitive ionophore and pH calibration resulted in slopes of 55 mV decade-1 over a pH range from 11 to 6. OPH was isolated from recombinant Escherichia coli DH5 alpha and immobilized within poly(carbamoyl sulfonate) prepolymer on the surface of the H(+)-sensitive electrode without any further fixation membrane. OPH catalyzes the hydrolytic cleavage of OP compounds which releases protons in a concentration proportional to hydrolyzed substrate. Sensor performance was investigated with regard to enzyme load, concentration, pH and temperature of the measuring buffer using paraoxon as analyte. Best sensitivity and response time were obtained with sensors prepared with 250 U of OPH and measuring at 37 degrees C in 1.0 mM HEPES buffer, pH 9.3, containing 100 mM NaCl. The enzyme sensor exhibited a linear calibration range of 0.01-0.15 mM chlorpyrifos, 0.05-0.35 mM diazinon, 0.05-0.4 mM paraoxon and 0.007-0.05 mM parathion, respectively. For all these analytes response times to reach 95% of maximum change in potential did not exceed 5 min. Sensors stored under dry conditions at 4 degrees C still showed 60% of initial hydrolytic rate after 70 d. The sensors even when stored dry were ready for measurements after 5 min incubation in measuring buffer. A range of putative interfering substances did not influence sensor response, and suitability of measuring OPs in soil extracts was ascertained.

A disposable biosensor for urea determination in blood based on an ammonium-sensitive transducer

A potentiometric urea-sensitive biosensor using a NH + 4-sensitive disposable electrode in double matrix membrane (DMM) technology as transducer is described. The ion-sensitive polymer matrix membrane was formed in the presence of an additional electrochemical inert filter paper matrix to improve the reproducibility in sensor production. The electrodes were prepared from one-side silver-coated filter paper, which is encapsulated for insulation by a heat-sealing film. A defined volume of the NH + 4-sensitive polymer matrix membrane cocktail was deposited on this filter paper. To obtain the urea-biosensor a layer of urease was cast onto the ion-sensitive membrane. Poly (carbamoylsulfonate) hydrogel, produced from a hydrophilic polyurethane prepolymer blocked with bisulfite, served as immobilisation material. The disposable urea-sensitive electrode was combined with a disposable Ag/AgCl reference electrode to obtain the disposable urea biosensor. The sensor responded rapidly and in a stable manner to changes in urea concentrations between 7.2×10 −5 and 2.1×10 −2 mol/l. The detection limit was 2×10 −5 mol/l urea and the slope in the linear range 52 mV/decade. By taking into consideration the influence of the interfering K +- and Na +- ions the sensor can be used for the determination of urea in human blood and serum samples (diluted or undiluted). A good correlation was found with the data obtained by the spectrophotometric routine method.

Disposable ion-selective electrodes

In this paper we describe a low-cost ion-selective electrode in double matrix membrance technology. This sensor is prepared from filter paper with an evaporated silver conducting line on one side. For insulation the sensor is laminated with a preperforated heat-sealing film. A coated film sensor in double matrix membrane technology is produced by filling one hole with a defined volume of an ion-selective polymer matrix membrane cocktail. The double matrix membrane (DMM) is formed by the polymer matrix membrane and the additional microfibre matrix (MFM) of the filter paper. Such sensors can be produced in a batch process. Therefore mass-production of low-cost sensors is possible. The response behaviour of the low-cost ion-selective electrode is comparable to that of conventional macro ion-selective electrodes.

Potentiometric biosensor in double matrix membrane technology

A throw-away urea sensor is described. A pH-sensitive disposable sensor constructed using double matrix membrane technology was used as a transducer. Double matrix membrane technology describes a process where an ion-sensitive polymer matrix membrane is formed in the presence of an additional inert matrix for to improve the reproducibility of sensor production. In this case one-side silver-coated filter paper was used as the inert matrix which was encapsulated by a heat sealing film. A pH-sensitive membrane was casted into this filter paper and on the surface of this membrane a urease containing layer was deposited. The sensor responded to between 10 −2 mol/l and 10 −4 mol/l urea, the response slope was 32·7 mV/decade. The concentration range in which the sensor responds is important for clinical analysis. The main advantages of this pH-based urea electrode include miniature size as well as simple and low cost fabrication in a batch process.

Disposable sodium electrodes

In this paper we describe a disposable sodium sensor in double matrix membrane technology. This sensor is prepared from filter paper with an evaporated silver conducting line on one side. For insulation the sensor is laminated with a pre-perforated heat-sealing film. A defined volume of an ion-sensitive polymer matrix membrane cocktail is filled into one hole. So an ion-sensitive coated film sensor in double matrix membrane technology is produced. The double matrix membrane is formed by the polymer matrix membrane and by the additional filter paper matrix. The response behaviour of the sodium electrode is comparable with conventional macro ion-selective electrodes. By this technology a mass production of low cost sensors is possible.