G. A. Rechnitz

Plant tissue-based bioselective membrane electrode for glutamate

Abstract A novel potentiometric membrane electrode with selective response to L-glutamate over the 2 × 10 -4 –1.3 × 10 -2 M concentration range is constructed by immobilizing slices of yellow squash tissue at a CO 2 gas sensor. This system represents the first successful use of intact plant materials as biocatalysts in the construction of bioselective potentiometric membrane electrodes; as a result, the range of future possibilities may be greatly extended. The glutamate-sensing electrode combines excellent selectivity characteristics over some 25 possible interferences tested, good reproducibility, and a useful lifetime of 7 days in aqueous samples.

Prototype Potentiometric Biosensor Using Intact Chemoreceptor Structures

Abstract Antennule structures from blue crabs are directly coupled with potentiometric electrodes to devise a novel type of biosensor. The prototype sensors are shown to yield sensitive and selective responses to amino acids in solution based upon nerve signals from the olfactory cheraoreceptors at the sensory tip of the antennule. Both single-unit and multi-unit responses can be observed and correlated with analytical variables.

Preparation and properties of an antibody-selective membrane electrode

Abstract A membrane electrode with selective response for the antibodies of the antigenic determinant dinitrophenol (DNP) has been devised by incorporating DNP—ion carrier conjugates in a polyvinyl chloride membrane matrix. Details of the preparative and immobilization procedures are provided along with an evaluation of optimum solution conditions for electrode use. The response mechanism of the antibody electrode is postulated to involve a “selectivity shift” effect.

Bound coefactor/dual enzyme electrode system for l-alanine

A dual enzyme-bound coenzyme electrode system for quantifying l-alanine is described. Commercially available dextran-bound NAD was incorporated into an l-alanine dehydrogenase (E.C. 1.4.1.1)/l-lactate dehydrogenase (E.C. 1.1.1.27) enzyme system and held at the surface of a potentiometric ammonia gas sensor. Using this system, l-alanine calibration curves with a slope of 45 mV/decade and 10−5 M detection limit were obtained with a sensor lifetime of at least 10 days. This system is potentially useful for the clinical determination of l-alanine in serum.

Monoclonal antibody biosensor for antigen monitoring

Abstract A new class of fully reversible biosensors, utilizing a layer of monoclonal antibodies trapped at the sensing surface of an immobilized-antigen membrane, is shown to be suited for continuous monitoring of antigen levels. The model sensor described gives a potentiometric response to the hapten 2,4-dinitrophenol (DNP) at micromolar concentration levels through competitive interaction with monoclonal anti-DNP antibodies held within the sensor tip. The proposed design yields a reusable, reagentless antigen sensor with good analytical precision and an operating lifetime of at least 17 days.

Bacterial membrane electrode for l-cysteine

Abstract Potentiometric response to L-cysteine is obtained by coupling bacteria of the type Proteus morganii to a modified version of a hydrogen sulfide gas-sensing membrane electrode. The resulting electrode system shows good response to cysteine in the millimolar concentration range with moderate selectivity over related sulfur-containing amino acids. The practical applicability of the electrode is limited by the poor discrimination of the internal gas sensor between hydrogen sulfide and carbon dioxide.

Induced bacterial electrode for the potentiometric measurement of tyrosine

A bacterial tyrosine-selective potentiometric electrode is proposed in which the desired biocatalytic activity is biochemically induced during growth of the bacterial cells. As the result of this induction, a normally ineffective biocatalyst, Aeromonas phenologenes ATCC 29063 can be coupled with an ammonia gas-sensing electrode in order to produce a useful tyrosine-selective electrode. The sensor shows excellent response characteristics, having a slope of 50–58 mV/decade, a range of logarithmic response from 8.3 × 10-5 M to 1.0 × 10-3 M tyrosine, a lower limit of detection of 3.3 × 10-5 M tyrosine, response times of 4–6 min, and a useful lifetime in excess of one week. Specific enzyme inhibitors are employed to enhance the selectivity of the electrode while maintaining high biocatalytic activity with respect to tyrosine.

Enzyme electrode for the determination of salicylate

Abstract Salicylate hydorxylase is used with a carbon dioxide sensor for the determination of salicylate in aqueous solution and pooled serum. The enzyme is physically entrapped with a dialysis membrance at the sensing tip of the carbon dioxide electrode. The enzyme catalyses the stoichiometric formation of catechol and carbon dioxide from salicylate and reduced pyridine nucleotide in the presence of flavin adenine dinucleotide as a specific cofactor. The carbon dioxide is detected by the sensor and related to the concentration of salicylate via a calibration curve. The method compares favorably with the spectrophotometric method for assay of salicylate. Although suitable for salicylate concentrations in the range of 5–300 μg ml −1 , its response below 5 μg ml −1 is limited by the detection limit of the carbon dioxide sensor.

The development of biocatalytic membrane electrodes

Abstract Recent developments and future prospects of biocatalytic membrane electrodes are examined in the light of past experience. The influences of scientific, economic and human factors on the course of development is evident.

Determination of glutamine in cerebrospinal fluid with a tissue-based membrane electrode

A glutamine-selective sensor consisting of porcine kidney tissue immobilized at an ammonia gas electrode is utilized. It yields good precision and accuracy over the clinically important range of glutamine concentrations (10-4–10-2 M).