Isao Karube

Biosensors : Fundamentals and Applications

This truly interdisciplinary work is the first substantial and comprehensive book to describe the biosensor, an important new technology combining the specificity and sensitivity of biological syst ...

A comparison of screening methods for antioxidant activity in seaweeds

The inhibition of lipid peroxidation and radical scavenging effects were studied to evaluate the antioxidant activity for extracts of 17 species of seaweed. The antioxidant effect was evaluated by determination of lipoxygenase activity and by α, α-diphenyl-β-picrylhydrazyl (DPPH) decolorization. Lipoxygenase activity was depressed in the presence of aqueous and ethanol extracts of 4 algal species; Sargassum species had the highest antioxidant activity of all the species examined. The ethanol extracts of one Sargassum species showed competitive inhibition with the substrate. The same species also showed radical scavenging activity in the DPPH decolorization test. Comparison of these results shows no relationship between enzyme inhibition and radical scavenging activity.

CO2 fixation from the flue gas on coal-fired thermal power plant by microalgae

In order to convert CO2 into biomass by solar energy, we have conducted studies to define growth characteristics of microalgae under various culture conditions. First, we screened microalgae having high temperature and high CO2 resistance. Algae were grown at 35°C and 15% CO2. As a result, we have obtained the strain T-1 of Chlorella which was found to be high temperature tolerant as well as have high growth rate at 15% CO2 concentration. Subsequently we study growth rates under various combinations of SOx and NOx. Their results indicate that Chlorella sp. T-1 can be an ideal candidate for biological fixation of CO2 exhausted by coal-fired thermal power plants. Then, in order to confirm the CO2 fixation efficiency in the actual basis flue gas. The result indicated that Chlorella sp. T-1 has sufficient growth rate despite the condition very severe for the growth of living creatures in the flue gas containing SOx, NOx, Dust and variety of trace elements, we could confirm that it has an excellent applicability to actual basis flue gas.

Tolerance of microalgae to high CO2 and high temperature

We have screened five green freshwater microalgae for tolerance to high CO2 concentrations. Scenedesmus and Chlorella showed much higher log phase growth rates than the other three strains tested. Scenedesmus was better able to tolerate very high CO2 concentrations than Chlorella. However, both algae had about the same growth rate when the CO2 concentration was in the range 10–30%. Chlorella was better able to tolerate elevated temperatures. The two algae had very similar light response curves. Scenedesmus was completely inhibited by 100% CO2. This inhibition was reversible since growth was resumed when the CO2 concentration was returned to 20%.

Atrazine sensing by molecularly imprinted membranes

Abstract New types of polymeric membranes containing molecular recognition sites for atrazine have been prepared using the molecular imprinting approach. The membrane synthesis includes radical polymerization of diethyl aminoethyl methacrylate and ethylene glycol dimethacrylate in the presence of atrazine as template. After splitting off the template molecules, these polymers have been used as materials for conductimetric sensors, sensitive for the herbicide. Influence of polymerization conditions on membrane sensitivity and nature of sensor response is discussed. With this system atrazine in solution can be detected in the range 0.01–0.50 mg/L. Although this dynamic range is at present not large, the membranes did not show loss of sensitivity for at least 4 months. The response time for the sensor is in the order of 30 min, which might be reduced using thinner imprinted membranes.

Molecularly imprinted polymers for biosensor applications

Abstract Molecular imprinting, which allows the formation of specific recognition sites in polymer matrices, is now applied widely for developing robust sensors for industry, diagnostics, and environmental analysis. In these sensors, molecularly imprinted polymers are coupled with appropriate transducers for the quantitative detection. This article describes recent trends and some examples of sensors based on molecular imprinting.

Integrated biosensor for glucose and galactose

Abstract A glucose microsensor based on quinoprotein glucose dehydrogenase (GDH) and electron mediators is described. It is unaffected by the concentration of dissolved oxygen. Its calibration graph is linear below 10 mg dl −1. The insensitivity to oxygen arises because the concentration of the oxidized forms of the mediators is insufficient to oxidize the reduced form of GDH. An integrated microsensor for glucose and galactose based on GHD and galactose oxidase was constructed. Glucose and galactose concentrations were determined from the current increase due to oxidation of the mediators or the current decrease due to reduction of oxygen.

Optical detection of chloramphenicol using molecularly imprinted polymers

A practical optical sensing system for the determination of chloramphenicol (CAP), utilizing molecularly imprinted polymers (MIPs) and HPLC, has been developed. The method is based on competitive displacement of a chloramphenicol-methyl red (CAP-MR) dye conjugate from specific binding cavities in an imprinted polymer by the analyte. The best of these polymers was obtained using (diethylamino)ethyl methacrylate as functional monomer at a monomer:template ratio of 2:1. HPLC with a mobile phase containing CAP-MR was used as the detection system, and injection of CAP and, to a lesser degree, thiamphenicol resulted in proportional displacement of the conjugate, which was detected at 460 nm. The detection system showed a linear response over a range of 3-1000 μg/mL and effectively detected CAP extracted from serum. This system offers a tailor-made, selective, and rapid method for CAP detection, is able to discriminate between similar molecules, and is effective below and above the therapeutic range (10-20 μg/mL serum, potentially toxic above 25 μg/mL). This technique is quite general and should enable the use of MIPs in a wide variety of applications involving the detection of families of molecules which possess a distinct arrangement of functional groups.

Acetylcholinesterase in organic solvents for the detection of pesticides: Biosensor application

Abstract Acetylcholinesterase (AChE) from electric eel, in a free or immobilized state, can be used for the detection of insecticides. This system is convenient because of the selectivity and specificity of the inhibition of AChE by organophosphorus and carbamate insecticides. However, these pesticides are highly soluble only in organic solvents. This article deals with the determination of the activity of AChE in organic solvents. Firstly, the effect of different organic solvents on activity was determined using the free enzyme. The AChE activity was maintained using the free enzyme. The AChE activity was maintained depending on the nature of the solvent. The results were applied to the biosensing system and a new method for the detection of organophosphorus and carbamate insecticides was developed. A correlation between the AChE activity and a physico-chemical parameter, was found in order to predict the effect of the solvent on enzyme activity. Upon comparison of the correlation curve obtained with free and immobilized enzyme, it appeared that immobilization enhanced the stability of the enzyme and increased the number of usable organic solvents. The inhibition of AChE by organophosphorus and carbamate insecticides was tested in organic solvents and the limit of detection determined. The inhibitory capacity of AChE was maintained in most organic solvents. The reactivation of immobilized enzyme with 2-pyridine aldoxime methiodide (2-PAM) allowed the repeated use of the same enzyme electrode. The application of the biosensor for the detection of organophosphorus and carbamate insecticides in organic solvents using chemical knowledge will be useful for the detection of pesticide residues present in water and food at very low levels.

Problems associated with the thin-film Ag/AgCl reference electrode and a novel structure with improved durability

Abstract We have developed a novel thin-film Ag/AgCl reference electrode which shows dramatic improvement in its durability. To make the electrode resistant to heat treatment in its fabrication, a metal adhesive layer in the currently used thin-film Ag/AgCl electrodes was replaced by a polyimide layer, and a gold backbone structure was employed. Unlike the currently used structure, the entire surface of the silver layer was covered with a polyimide layer and AgCl was grown from the periphery of the pattern. The structure was resistant to baking at 300°C. Whereas the currently used Ag/AgCl electrode has a very short lifespan in concentrated KCl solutions, the novel electrode showed surprising resistance in these solutions. In a KCl and AgCl saturated solution, the novel electrode gave a stable potential for approximately 8 h, while the currently used electrode functioned for only 1.5 min. A dramatic difference was also observed in the resistance to interfering materials. Although 1 mM KI or K 2 S was enough to break the currently used electrode, the novel electrode was resistant to these materials and showed much smaller potential shift. In the novel Ag/AgCl structure, the rate of AgCl formation was significantly delayed and the spread of the AgCl layer was visualized. Therefore, any of the electrochemical and chemical methods of AgCl formation could be easily applied.