Stanisław Głąb

Disposable strip potentiometric electrodes with solvent-polymeric ion-selective membranes fabricated using screen-printing technology

A simple and reproducible method for mass production of disposable, plastic, thick-film, ion-selective electrodes using screen-printing technology is described. The properties of selective sensors for potassium, ammonium and nitrate ions obtained with this technology are shown and discussed. All the obtained strip sensors have analytical characteristics (sensitivity, selectivity, dynamic range and response time) comparable with those for conventional ion-selective electrodes. However, they practically do not require any conditioning before measurements and they respond in short time (steady-state signal is reached after a few seconds), that is important in case of the disposable sensors.

Optical biosensors based on Prussian Blue films

Optical biosensing schemes based on enzymatically modified inorganic/organic transparent films predominately composed of Prussian Blue are demonstrated. The composite film, which is non-electrochemically deposited on a non-conducting support. is used as an optical transducer for flow-through biosensors based on hydrolases and oxidases. Urease and glucose oxidase are utilized as model enzymes. Action of the urea biosensor is based on optical pH sensitivity of Prussian Blue indicator. The glucose biosensor is acting as first-generation optical biosensor based on in situ generated Prussian White transducer for hydrogen peroxide. These simple, single-pass transmission optical biosensors exhibit sensitivity in the millimolar range of concentration. The biosensors are very stable owing to presence of a poly(pyrrolylbenzoic acid) network in the composite material. This organic polymer plays a dual role as a binding agent for inorganic material and as a functionalized support for strong covalent immobilization of enzyme molecules.

Application of Prussian blue-based optical sensor in pharmaceutical analysis

Optical flow-through cell-detector with incorporated transparent chemosensitive layer of Prussian blue has been applied in simple, single-channel flow-injection system for pharmaceutical analysis. The reductant analyte converts the Prussian blue based sensing layer to Prussian white form, and the attendant color change is used for sensing. Discoloration of the film is spectrophotometrically detected at 720 nm wavelength. The flow injection system has been successfully used for selective determination of ascorbic acid in simple and complex pharmaceuticals. The method is free from interferences caused by various ions and active ingredients commonly found in pharmaceuticals. The flow-through sensor is useful for spectrophotometric flow-injection analysis of intensively colored and turbid samples. The results of medicine analysis are comparable to those obtained using reference pharmacopeal method. The analytical system could be also used for determination of cysteine and hydrogen peroxide in medicines.

Prussian blue-based optical glucose biosensor in flow-injection analysis

A novel optical biosensor for glucose and its analytical applications are demonstrated. The biosensing part of the flow-through sensor is composed of Prussian blue (PB) film with chemically linked molecules of glucose oxidase (GOx). The utilized biosensing scheme is similar to this reported for oxidase-based first-generation amperometric biosensors. Demonstrated biosensing system exhibits excellent operational (over 1 month) and storage (at least 3 months) stability. Developed flow-injection systems based on the PB/GOx-optical biosensor allow frequent measurements (15 samples/h) in sub-millimolar range of glucose concentration (linear responses from 0.05 to 2.0 mmol/l). Double-channel flow-injection analysis (FIA)/biosensor system has been successfully used in pharmaceutical, food and clinical analysis of real samples containing glucose.

Potentiometric determination of dialysate urea nitrogen

An enzymatically modified ammonium ion-selective electrode has been applied for the determination of urea in spent dialysate. The biosensor has been used in a simple flow-injection analysis (FIA) system. The system enables one to perform over 25 dialysate urea nitrogen (DUN) determinations per hour. The interferences from other components of posthemodialysis fluid were eliminated by simultaneous measurements with non-modified enzymatically ion-selective electrode. It is possible to use both the sensors in a simplified differential potentiometric system. The results of DUN determination using the biosensor/FIA system and a conventional method of urea determination were comparable. The presented analytical system can potentially find wider biomedical application in the monitoring of hemodialysis progress.

Urea Biosensors Based on PVC Membrane Ion-Selective Electrodes

Abstract This paper presents a general method of enzyme immobilization at the surface of ion selective membranes. Covalent binding of enzymes directly on the electrode surface is a very effective method that results in stable enzymatic membranes. As an example the construction of enzymatic sensors for urea determination based on ammonium and hydrogen carbonate ion selective electrodes is presented. The optimum working conditions for these biosensors were found. Bioelectrodes based on an ammonium sensor show very good analytical parameters: dynamic stability - over 2 months without decrease of sensitivity, response time - shorter then 20 s. high sensitivity, determination range from 0.3 to 70 mM. In the contrast to the ammonium ion based biosensors, those constructed on the basis of anion selective electrodes have worse analytical parameters. It is mainly due to poor selectivity and instability of an applied ion selective electrode. In spite of this, both types of urea biosensors were used for measurements...

Kinetic model of pH-based potentiometric enzymic sensors. Part 3. Experimental verification

An experimental verification of the kinetic model for a pH-based potentiometric enzymic sensor is presented. For this purpose the experimental results obtained using a urea sensor prepared by the immobilization of urease on the hydrogen ion sensitive surface of a glass electrode were employed. The effects of buffer capacity and pH and also the rate of solution stirring on the electrode response were examined and the results obtained were compared with those predicted theoretically. The influence of local changes in pH within the enzymic layer of the sensor on the enzyme kinetics is also discussed.

POTENTIOMETRIC THICK-FILM GRAPHITE ELECTRODES WITH IMPROVED RESPONSE TO COPPER IONS

Thick-film graphite electrodes produced by screen-printing have been investigated as inexpensive disposable potentiometric sensors for determination of heavy metal ions. The modification of graphite paste with copper sulfides caused an improvement of the analytical characteristics of the sensors. The electrodes based on Cu2S-doped graphite film are useful for reproducible, fast, and selective determination of copper ions with Nernstian sensitivity in a wide range of concentration.

Potentiometric biosensor for control of biotechnological production of penicillin G

A pH-membrane electrode with tridodecylamine as a hydrogen ion-selective ionophore was used for the construction of a biosensor for the benzylpenicillin determination. The electrode was enzymatically modified by covalent binding of penicillinase directly to the membrane surface. The high sensitivity and short response time of the biosensor allow its application in flow injection analysis (FIA). Up to 30 samples per hour can be analyzed in the flow system. The FIA system with the biosensor was successfully used for the determination of penicillin G in fermentation broth. An optimized analytical procedure results in minimization of interferences from pH and buffer capacity of the real samples. No interferences from inorganic, organic and bioorganic components present in the fermentation medium were observed. An important advantage of the presented analytical system is the long-term stability due to the long lifetime of the biosensor. Consequently fermentation bioprocesses can be controlled using the same biosensor for about two months. Due to the high sensitivity and selectivity, the presented method for the penicillin determination in real biotechnological samples gives analytical results comparable to those obtained using methods recommended by pharmacopoeias.

pH-metric detection of alkaline phosphatase activity as a novel biosensing platform

A detection of alkaline phosphatase (ALP, EC 3.1.3.1) activity by the monitoring of pH changes caused by the biocatalytic action of the enzyme has been experimentally examined. Enzymatically catalyzed hydrolysis of monofluorophosphate has been found to be the best basis for such measurements. Protolytic equilibria connected with the developed biosensing system were recognized and the optimal conditions for the assay have been found. Advantages and disadvantages of the developed (bio)sensing scheme have been discussed. The prototype of pH-ALP based enzyme electrode has been demonstrated. Potential utility of such substrate-enzyme-sensor system for the development of a new group of biosensors has been announced.