Organic phase enzyme electrodes: applications and theoretical studies

Microfluidics Integrated Biosensors: A Leading Technology towards Lab-on-a-Chip and Sensing Applications

A biosensor can be defined as a compact analytical device or unit incorporating a biological or biologically derived sensitive recognition element immobilized on a physicochemical transducer to measure one or more analytes. Microfluidic systems, on the other hand, provide throughput processing, enhance transport for controlling the flow conditions, increase the mixing rate of different reagents, reduce sample and reagents volume (down to nanoliter), increase sensitivity of detection, and utilize the same platform for both sample preparation and detection. In view of these advantages, the integration of microfluidic and biosensor technologies provides the ability to merge chemical and biological components into a single platform and offers new opportunities for future biosensing applications including portability, disposability, real-time detection, unprecedented accuracies, and simultaneous analysis of different analytes in a single device. This review aims at representing advances and achievements in the field of microfluidic-based biosensing. The review also presents examples extracted from the literature to demonstrate the advantages of merging microfluidic and biosensing technologies and illustrate the versatility that such integration promises in the future biosensing for emerging areas of biological engineering, biomedical studies, point-of-care diagnostics, environmental monitoring, and precision agriculture.

Kinetics of hydrogen peroxide decomposition by catalase: hydroxylic solvent effects

The effect of water-alcohol (methanol, ethanol, propan-1-ol, propan-2-ol, ethane-1,2-diol and propane-1,2,3-triol) binary mixtures on the kinetics of hydrogen peroxide decomposition in the presence of bovine liver catalase is investigated. In all solvents, the activity of catalase is smaller than in water. The results are discussed on the basis of a simple kinetic model. The kinetic constants for product formation through enzyme-substrate complex decomposition and for inactivation of catalase are estimated. The organic solvents are characterized by several physical properties: dielectric constant (D), hydrophobicity (log P), concentration of hydroxyl groups ([OH]), polarizability (α), Kamlet-Taft parameter (β) and Kosower parameter (Z). The relationships between the initial rate, kinetic constants and medium properties are analyzed by linear and multiple linear regression.

Acetylcholinesterase (AChE) Electrodes Based on Gelatin and Chitosan Matrices for the Pesticide Detection

Enzyme electrodes for the determination of organophosphate pesticides were developed by using acetylcholinesterase (AChE) in combination with a pH electrode. AChE was immobilized on the surface of pH electrode by using gelatin and chitosan membranes, respectively. The measurement system is based on potentiometric detection of the inhibiting properties of organophosphates on enzyme activity. The phosphate buffer (2.5mM, pH 8.0) and the borate buffer (2.5mM, pH 8.5) at 25 degrees C were established as providing the optimum conditions for the gelatin and chitosan based biosensor systems, respectively. Furthermore, operational, thermal, and organic phase stabilities were also tested. Linear ranges for different organophosphates such as malathion, parathion-methyl, and methamidophos were detected by using both types of biosensor system. Moreover, as well as accuracy, the regeneration conditions by using pyridine-2-aldoximethiodide (PAM-2) as a reactivating agent for the inhibited electrodes were also investigated.

(Bio)Sensor Approach in the Evaluation of Polyphenols in Vegetal Matrices

Polyphenols are compounds widely distributed in the plant kingdom and have attracted much attention, because of their health benefits and important properties such as radical scavenging, metal chelating agents, inhibitors of lipoprotein oxidation, anti-inflammatory and anti-allergic activities. Due to their important role in the diet and in therapy, it is important to estimate their content in the different matrices of interest. Besides classical analytical methods, new emerging technologies have also appeared in the last decade aiming for simple and eventually cheap detection of polyphenols. This review focused on the recent applications of biosensing-based technologies for polyphenol estimation in vegetal matrices, using different transduction principles. These analytical tools are generally fast, giving responses in the order of a few seconds/minutes, and also very sensitive and generally selective (mainly depending on the enzyme used). Direct measurements in most of the investigated matrices were possible, both in aqueous and organic phases.

Organic phase enzyme electrodes

In the development of biosensors, organic phase enzyme electrodes (OPEEs) have received considerable attention for the detection of substrates in organic media. This article reviews different enzymes, transductors and immobilization methods used for the preparation of OPEEs in the last decade.

Characterization of an organic phase peroxide biosensor based on horseradish peroxidase immobilized in Eastman AQ

Due to their frequent occurrence in food, cosmetics and pharmaceutical products, and their poor solubility in water, the detection of peroxides in organic solvents has aroused significant interest. For diagnostics or on-site testing, a fast and specific experimental approach is required. Although aqueous peroxide biosensors are well known, they are usually not suitable for nonaqueous applications due to their instability. Here we describe an organic phase biosensor for hydrogen peroxide based on horseradish peroxidase immobilized in an Eastman AQ 55 polymer matrix. Rotating disc amperometry was used to examine the effect of the solvent properties, the amount and pH of added buffer, the concentration of peroxide and ferrocene dimethanol, and the amount of Eastman AQ 55 and of enzyme on the response of the biosensor to hydrogen peroxide. The response of the biosensor was limited by diffusion. Linear responses (with detection limits to hydrogen peroxide given in parentheses) were obtained in methanol (1.2 microM), ethanol (0.6 microM), 1-propanol (2.8 microM), acetone (1.4 microM), acetonitrile (2.6 microM), and ethylene glycol (13.6 microM). The rate of diffusion of ferrocene dimethanol was more constrained than the rate of diffusion of hydrogen peroxide, resulting in a comparatively narrow linear range. The main advantages of the sensor are its ease of use and a high degree of reproducibility, together with good operational and storage stability.

Bioelectronic sniffer for nicotine using enzyme inhibition

A novel bioelectronic sniffer for nicotine in the gas phase was developed with enzyme inhibition principle to butyrylcholinesterase activity. The bioelectronic devices for nicotine in the gas and liquid phases were constructed using a Clark-type dissolved oxygen electrode and a membrane immobilized butyrylcholinesterase and choline oxidase. After the assessment of the sensor performances to choline and butyrylcholine as pre-examinations, the characteristics of the biosensor and bio-sniffer for nicotine were evaluated in the liquid and gas phases, respectively. The sensor signal of the bio-devices with 300 micromol l(-1) of butyrylcholine decreased quickly following application of nicotine and reached to the steady-state current, thus relating the concentration of nicotine in the liquid and gas phases. The biosensor was used to measure nicotine solution from 10 to 300 micromol l(-1). In the gas-phase experiment, the current signal of the bio-sniffer was also found to be linearly to the nicotine concentration over the range of 10.0-1000 ppb including 75.0 ppb as threshold limit value (TLV) by American Conference of Governmental Industrial Hygienists (ACGIH).