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An amperometric enzyme biosensor for the direct measurement of parathion was developed. The biosensor is based on parathion hydrolase from Pseudomonas sp. isolated from contaminated soil. The enzyme, which was immobilized on a carbon electrode, catalyzes the hydrolysis of parathion to form p-nitrophenol, which was detected by its anodic oxidation. The enzymatic and electrochemical reactions were examined and optimized. Screen-printed electrodes and a microflow injection system provide the means to significantly reduce the volume of the detected samples. Pulsed techniques further increased the sensitivity of the measurement. The current signal was linearly related to the parathion concentration, and the detection limit was less than 1 ng/mL. The biosensor is rapid as well and can be used outdoors and indoors by a nonqualified person.

The increasing demand for on-line measurement of milk composition directs science and industry to search for practical solutions, and biosensors may be a possibility. The specific objective of this work was to develop an electrochemical biosensor to determine lactose concentration in fresh raw milk. The sensor is based on serial reactions of three enzymes--beta-galactosidase, glucose oxidase, and horseradish peroxidase--immobilized on a glassy carbon electrode. The sequential enzymatic reactions increase the selectivity and sensitivity of the sensor. The sensor requires dilution of the raw milk and the addition of 5-aminosalicylic acid. Lactose concentrations in raw milk measured by the sensor were in good agreement with those measured by a reference laboratory using infrared technology. The results were obtained in milk samples that varied in fat and protein composition. From the results, we conclude that an electrochemical biosensor for determination of lactose concentration in fresh raw milk can be developed, and that the biosensor presented in this study maintained the qualities required for further development into an online sensor in the milking parlor.

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