Mihaela Niculescu

Quinohemoprotein alcohol dehydrogenase-based reagentless amperometric biosensor for ethanol monitoring during wine fermentation

This paper describes the development and optimization of an amperometric biosensor for monitoring ethanol in beverages. The biosensor is constructed by cross-linking a quinoprotein alcohol dehydrogenase (QH-ADH) to an Os-complex-modified poly(vinylimidazole) redox polymer using poly(ethylene glycol) diglycidyl ether. The optimum biosensor configuration was evaluated by changing the ratio between enzyme, redox polymer, and cross-linker using conventional graphite rods as basis electrodes. The optimized sensor showed a sensitivity of 0.336+/-0.025 A M-1 cm(2) for ethanol and a detection limit (calculated as three times the signal-to-noise ratio) of 1 muM. This biosensor configuration was further evaluated in a conventional flow-injection system and the applicability for the determination of ethanol in diverse wine samples could be successfully demonstrated. Adaptation of this sensor configuration to screen-printed (SP) electrodes allowed their integration into an automated sequential-injection analyzer and the successful on-line monitoring of ethanol during wine fermentation processes. (Less)

Direct bioelectrocatalysis at carbon electrodes modified with quinohemoprotein alcohol dehydrogenase from Gluconobacter sp. 33

A newly isolated, purified, and characterized PQQ-dependent alcohol dehydrogenase (a bacterial membrane-bound protein) was recently found to display a surprisingly large linear range and high selectivity towards ethanol when integrated into a conducting polymer network on a platinum electrode. These findings motivated us to study the enzyme when simply immobilized onto carbonaceous surfaces in order to establish its characteristics and suitability for sensor development, the sensor design being based on a direct-electron transfer pathway. Graphite rods and screen-printed electrodes were modified in two different ways, and were operated both in FIA and batch mode. The obtained biosensor characteristics were highly dependent on the sensor architecture, the highest sensitivity (179 mA M-1 cm(-2)) and lowest detection limit (1 muM) being obtained for screen-printed electrodes used in a batch mode. A mechanism of the observed direct electron transfer between the enzymes active center and the electrode is proposed. (Less)

Simultaneous detection of ethanol, glucose and glycerol in wines using pyrroloquinoline quinone-dependent dehydrogenases based biosensors

Amperometric biosensors based on corresponding dehydrogenases have been developed for the determination of ethanol, glucose and glycerol. The enzymes have been integrated in redox hydrogels using an Os complex-modified non-conducting polymer employed as the electrochemical mediator and poly(ethyleneglycol)-diglycidyl ether (PEGDGE) as the cross-linking agent. The developed biosensors showed a sensitive response to ethanol, glucose and glycerol within the concentration range 2.5–250, 20–800, and 1–200 M, detection limits of 1.2, 9 and 1 M, and sensitivities of 220, 87 and 32 mA M−1 cm−2, respectively. The ethanol, glucose and glycerol content of several types of wine was determined with these biosensors, and the results were compared with those obtained by spectrophotometric methods. The developed biosensors have been successfully employed for simultaneous determination of all these substrates at the required sensitivity. (Less)

Glycerol dehydrogenase based amperometric biosensor for monitoring of glycerol in alcoholic beverages

Abstract Biosensors for measurement of glycerol in FIA were constructed using NAD+-dependent glycerol dehydrogenase (GlDH) either co-immobilized with phenazine methosulphate (PMS) or cross-linked to an Os-complex-modified poly(vinylimidazole) redox polymer (PVI13dmeOs) using poly(ethyleneglycole) diglycidilether (PEGDGE). The GlDH/PMS sensor was characterized by a linear range of 0.01–1 mM glycerol, a sensitivity of 1.83 mA/Mcm2, a detection limit (calculated as three times the signal-to-noise ratio) of 0.9 µM, and with 50% residual activity kept after 15 h of continuous operation at a sample throughput of 30 injections/h. The redox hydrogel-based biosensors showed the same dynamic range, but improved biosensors characteristics, i.e., a sensitivity of 4.79 mA/Mcm2, a detection limit of 0.1 µM, and a signal loss of only 20% after 15 h of operation in the same conditions. The optimized biosensor configurations were further used for analysis of glycerol in wine and the obtained results were compared with the ones obtained by spectrophotometrical experiments.

AMPEROMETRIC ENZYME-BASED BIOSENSORS FOR APPLICATION IN FOOD AND BEVERAGE INDUSTRY

Continuous, sensitive, selective, and reliable monitoring of a large variety of different compounds in various food and beverage samples is of increasing importance to assure a high-quality and tracing of any possible source of contamination of food and beverages. Most of the presently used classical analytical methods are often requiring expensive instrumentation, long analysis times and well-trained staff. Amperometric enzyme-based biosensors on the other hand have emerged in the last decade from basic science to useful tools with very promising application possibilities in food and beverage industry. Amperometric biosensors are in general highly selective, sensitive, relatively cheap, and easy to integrate into continuous analysis systems. A successful application of such sensors for industrial purposes, however, requires a sensor design, which satisfies the specific needs of monitoring the targeted analyte in the particular application, Since each individual application needs different operational conditions and sensor characteristics, it is obvious that biosensors have to be tailored for the particular case. The characteristics of the biosensors are depending on the used biorecognition element (enzyme), nature of signal transducer (electrode material) and the communication between these two elements (electron-transfer pathway).