Ahmad A. Suleiman

Piezoelectric crystal biosensors.

The recent development of piezoelectric devices as biosensors is reviewed. Biological materials, like enzymes, lipids, antibodies and antigens, have been used as specific coatings and were utilized for the determination of different substrates. Methods of protein coating and several applications are reported including microgravimetric immunoassays, microbial assays, DNA hybridization, enzyme detections and gas phase biosensors. Although the piezoelectric immunochemical sensor is convenient to use and very promising, a thorough understanding of the different phenomena associated with crystals frequency measurement in biological reactions is still lacking and deserves further investigation.

Recent developments in piezoelectric immunosensors. A review

The development of piezoelectric (PZ) devices as immunosensors is reviewed. The recent advances in sensor design have stimulated great interest in PZ technology and facilitated diverse applications in a variety of matrices. Methods of antibody immobilization on crystals and several applications are reported including microgravimetric immunoassays, microbial toxins and other contaminants.

Flow-injection determination of ethanol by fiber-optic chemiluminescence measurement

Abstract A new approach for the determination of ethanol in beverages is presented. The hydrogen peroxide generated in the enzymatically catalyzed oxidation of ethanol is measured by the luminol chemiluminescence reaction using potassium hexacyanoferrate(III) as a catalyst. Alcohol oxidase is immobilized on aminopropyl glass beads packed in a glass column. The chemiluminescence measurement is made using an optical fiber to transport the luminescence from the flow cell to the detector in conjunction with a flow system. This assay system responds linearly in the ethanol concentration range 3 × 10−6-7.5 × 10−4 M with a precision of 2.4% and an analysis time of 1.5 min.

Determination of urea in serum by a fiber-optic fluorescence biosensor.

A new fiber-optic biosensor for urea has been developed, based on immobilized urease coupled to a fluorescence ammonia sensor. The enzymatically generated ammonia diffuses through the membrane into a solution of the fluorescent pH indicator trisodium 8-hydroxypyrene-1,3,6-trisulfonate. The sensor has been successfully used for the determination of urea in serum samples, with results in good agreement with those reported by a local hospital. The proposed sensor is reversible and selective to urea. The ease of construction of the sensor tip offers the possibility of designing disposable tips for use in clinical applications.

Amperometric determination of phosphate by use of a nucleoside phosphorylase-xanthine oxidase enzyme sensor based on a clark-type hydrogen peroxide or oxygen electrode

A bienzymatic sensor for the determination of phosphate was constructed by coimmobilization of xanthine oxidase (EC 1.2.3.22) and nucleoside phosphorylase (EC 2.4.2.1) on a polycarbonate membrane mounted on the tips of amperometric hydrogen peroxide and oxygen electrodes. The sensor response was linear to phosphate concentrations in the range 10-250 microM.

Enzyme-Based Fiber Optic Sensor for Glucose Determination

Abstract A new fiber-optic probe for the determination of glucose is developed. Glucose oxidase is immobilized on a preactivated Immunodyne membrane by direct application of the enzymatic solution to one side of the membrane. The membrane is then placed around the common end of a bifurcated glass fiber optic bundle, and immersed in the sample cell which contains the glucose sample, peroxidase and a colorless dye. Glucose is quantified by the color change when the reaction takes place.

Piezoelectric (PZ) Immunosensors and Their Applications

Abstract The recent development of piezoelectric immunosensors is reviewed. The selectivity provided by the biological coatings together with the inherent sensitivity of the PZ devices and the ability to oscillate the crystal in liquid medium have induced a rising interest in this class of sensors. Methods of coating and several applications are reported including microgravimetric immunoassays, microbial assays and gas phase immunosensors.

PIEZOELECTRIC CRYSTAL SENSOR FOR THE DETERMINATION OF FORMALDEHYDE IN AIR

Formaldehyde in air was detected and assayed with a piezoelectric quartz crystal coated with a 7,10-dioxa-3,4-diaza-1,5,12,16-hexadecatetrol/chromotropic acid solution. Water vapor and several gaseous interferents were removed by passing the sampling stream through a column of anhydrous magnesium perchlorate. The response curves were linear in the concentration ranges 0.4-4.5 and 0.4-3.6 ppm v/v CH(2)O with and without the scrubber column, respectively. A single coating was used for 12 days (500 assays) without significant loss in sensitivity. With a single-point daily recalibration, the useful lifetime of the coating is about 2 months.

AMPEROMETRIC ASPARTATE ELECTRODE

Abstract An amperometric enzyme electrode for L -aspartate determination was developed. The probe consisted of a platinum electrode which senses hydrogen peroxide produced from the reactions catalyzed by two enzymes co-immobilized on a preactivated polymeric membrane, α-Ketoglutarate in the presence of L -aspartate was transaminated to L -glutamate by aspartate aminotransferase and the glutamate produced was oxidized by glutamate oxidase, with concomitant production of hydrogen peroxide. Additional protective membranes eliminated interferences from glutamate and most electroactive compounds. The response curve of the probe was linear over the concentration range 1.0 × 10−6 M to 2.0 × 10−4 M aspartate and was useful for at least two months. Aspartic acid in some pharmaceutical products was determined and the results correlated well with a liquid chromatographic reference method and the manufacturers specification.

A fiber optic biosensor for sulfite analysis in food.

The sulfite fiber optic biosensor developed herein is based on the enzymatic oxidation reaction of sulfite catalyzed by sulfite oxidase (SOD). The consumption of O(2) is measured with an O(2) fiber optic sensor which monitors the fluorescence quenching of the indicator, perylene, by molecular oxygen. Perylene is immobilized into a polymer matrix and attached to the end of a fiber bundle forming an O(2) sensor. The enzyme, sulfite oxidase is immobilized on a pre-activated membrane and mounted onto the O(2) sensor. Several analytical characteristics of this sulfite biosensor were investigated including dynamic range, reversibility, reproducibility, stability and selectivity. The sulfite contents of various food samples, e.g. dried fruits, potato flakes, lemon juice were determined and the results obtained were in good agreement with the standard AOAC method.