Garry A. Rechnitz

Flow Injection Immunosensing of Polycyclic Aromatic Hydrocarbons with a Quartz Crystal Microbalance

Abstract A piezoelectric immunosensor has been developed for the detection of various polycyclic aromatic hydrocarbons (PAHs). The antigen (benzo[a]pyrene–BSA conjugate, BaP–BSA) was immobilized through thioctic acid on gold coated quartz crystals, with a basic resonant frequency of 10xa0MHz. The monoclonal antibody 10c10 (mAb10c10), which specifically recognizes benzo[a]pyrene (BaP), was detected through frequency decreases (mass increase due to the immunoreaction). Determination of BaP was performed in the flow injection system by using a competitive pattern, in which BaP reacted with the bound mAb10c10 causing frequency increases. A nanomolar level of BaP can be detected with this immunosensor. The mAb10c10 modified quartz crystal cross-reacts with pyrene and naphthalene.

Voltammetry of Adsorbed Molecules. Part 2: Irreversible Redox Systems

Information about the kinetics of reactions can readily be extracted from linear sweep voltammograms of adsorbates which show irreversible behavior if the adsorbates behave ideally. Factors which cause nonideal behavior include lateral interactions between adsorbates, influence of solvent reorganization energies, and kinetic dispersion. The difficulties in extracting information on the kinetics of adsorbed redox systems which behave nonideally are discussed. Diagnostic criteria are provided from which it may be determined which of the above phenomena, if any, are effecting the voltammetric response.

Eggplant-based bioamperometric sensor for the detection of catechol

Abstract Polyphenol oxidases from eggplant have a high catalytic activity for the aerobic oxidation of catechol to o-quinone with selectivity over other phenolic substrates. An amperometric biosensor can therefore be constructed by incorporating selected portions of eggplant tissue in a carbon paste electrode. The proposed biosensor provides a selective response for catechol in the micromolar range, with a very fast response time and a useful lifetime of at least 3 weeks.

Kohlrabi-based amperometric biosensor for hydrogen peroxide measurement

Abstract Hydrogen peroxide was determined amperometrically in a steady-state arrangement by utilizing a kohlrabi - ferrocene based carbon paste electrode. A very short response time (2.6 seconds) and a relatively large usable pH range (5.0–7.4) were obtained. Several important hydrogen donors were studied as possible interferences.

Grape tissue-based electrochemical sensor for the determination of hydrogen peroxide

Abstract The use of grape tissue as a source of catalase for the determination of hydrogen peroxide is reported. A slice of grape tissue attached to the membrane of a Clark-type oxgen sensor was used to monitor the oxidation of hydrogen peroxide by catalase. At the steady state, the sensor responds linearly to hydrogen peroxide in the concentration range 1 × 10−5–5 × 10−4 M. The response time (T90) was of the order of 1 min for this sensor. No interference was observed from ethanol, amino acids, glucose and lactic acid. The long-term stability of the grape tissue sensor was much better than previously reported immobilized enzyme and liver tissue-based hydrogen peroxide sensors.

Dual-enzyme fiber optic biosensor for pyruvate

Abstract In this study, the response characteristics for a dual-enzyme fiber-optic biosensor for pyruvate are presented. An enzyme layer composed of lactate oxidase and lactate dehydrogenase (LDH) was fabricated at the tip of a sensing optrode. The biosensor is based on the luminescence detection of consumed reduced nicotinamide adenine dinucleotide (NADH) and the measured fluorescence intensity is related to the bulk concentration of pyruvate. Such a dual-enzyme optrode can not only retain the merits of fiber-optic biosensors, but can also take advantage of two enzyme-catalyzed reactions. The response sensitivity and detection limit of the proposed dual-enzyme sensors are improved by at least 8 and 5 times, respectively, compared to those of single-enzyme systems.

Improved plant tissue-based biosensor using in vitro cultured tobacco callus tissue

Abstract In vitro cultured tobacco callus tissue, which contains a high activity of peroxidase, was used to construct an amperometric biosensor for the detection of hydrogen peroxide. The tissue was incorporated into a carbon paste matrix along with ferrocene, an electron mediator. The detection of hydrogen peroxide was accomplished through its enzymatic reduction mediated by ferrocene. Comparison studies conducted with normally grown types of tobacco tissues indicate that the callus tissue has highest biocatalytic activity and the least variance between tissue preparations with respect to sensor response toward hydrogen peroxide. Additionally, the sensor exhibits a remarkably along lifetime of more than 5 months. Other important characteristics of the sensor include fast response times (less than 2 s), wide dynamic range (5 × 10 −6 -1.10 × 10 −4 M) and a detection limit of 7.5 × 10 −7 M hydrogen peroxide.

Nonisotopic receptor-binding assay for benzodiazepine receptors utilizing a fluorophore labeled ligand

A nonisotopic receptor-binding assay method provides a new approach for the study of receptor-ligand interactions and a possible receptor assay for benzodiazepine drugs. The proposed method is based upon the use of fluorescence-labeled drugs and a chromatographic system which accepts samples without deproteinization. The effectiveness of the technique is illustrated in a study of benzodiazepine receptor-drug-binding interactions.

Gold Electrode Modification with Thiolated Hapten for the Design of Amperometric and Piezoelectric Immunosensors

Self-assembly of a hapten monolayer is used for the development of amperometric and piezoelectric immunosensors. A disulfide compound carrying a terminal pyrene group was newly synthesized for the modification of a gold surface. The self-assembled organic monolayer was formed spontaneously through the use of a disulfide head group. The resulting monolayer and its long-term stability on a gold surface were measured by cyclic voltammetry. The application of the hapten monolayer to amperometric and piezoelectric immunosensing of monoclonal antibodies and benazo[a]pyrene (BaP) was also investigated.

Intact chemoreceptor biosensors based on Hawaiian aquatic species

Abstract Two species of Hawaiian crustaceans, Portunis sanguinolentus and Podophthalmis vigil, are shown to be effective for the construction of antennular receptrodes. The resulting chemoreceptor-based biosensors respond to stimulant compounds at levels below 10−15 M with very short response times. Experimental studies focused on trimethylamine oxide as a novel test compound, combined with chemometric techniques for data analysis, yield quantitative dose-response data over a wide concentration range.