Abstract: All-solid-state electrodes (without an internal contact solution), were constructed using a procedure which permitted the implementation of transducers in various configurations (cf., Biosensors Bioelectron. 1989, 4, 287). The transducers consisted of ammonium-selective PVC membranes applied directly on to conductive composite materials, e.g. graphite/epoxy composites. Urease was immobilized on to the PVC membranes, using the procedure of Kurmaran et al. (cf., Anal. Chem., 1991, 63, 1914) which allowed the deposition of an extremely thin layer of reticulated enzyme (1-2 µm) by means of an aerosol-spraying procedure. The resulting urea potentiometric biosensors exhibited a short response time (10 s) and a wide linear range (0.01-1 mM urea) with a sensitivity of 55 mV/decade. The lifetime of the sensor was ~40 days in periodical calibration use. A flow-through biosensor was also constructed using the same type of transducer and the same enzyme immobilization procedure for use in a FIA system. Using the flow-through sensor for the determination of 0.1 mM urea resulted in an RSD (n = 20) of 0.4%.

Abstract: A conducting polymer of poly 3,4-ethylenedioxythiophene (PEDT) was used as a matrix for entrapment of enzymes onto a platinum electrode surface in order to construct amperometric biosensors. Glucose oxidase (GOD) was used as an example, and it was entrapped in the polymer during the electrochemical polymerization. Glucose in oxygenated solutions was tested by amperometric measurements at +650 mV (vs. SCE) in a batch system. The influence of several experimental parameters in the electropolymerization process was explored to optimize the analytical performance. The detection limit and sensitivity for this biosensor were 4 x 10^-5 M and 15.2 mA M-1 cm-2, respectively. A linear range of response was found from 0.2 to 8 mM of glucose. The response time was 2-5 s. The stability of the electropolymerized films was evaluated in operational conditions. The glucose probe, stored in buffer at 4°C when not in use, showed a residual activity of 40% after about 1 month. Glucose in synthetic serum was determined under flow injection conditions using an amperometric flow cell. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract: This paper presents the construction of various biosensors using thin- film layers incorporated in flow injection devices, providing automated systems for biomedical analysis, process and environmental monitoring. A urease sensor has been developed in conjunction with a flow injection system for the automatic determination of urea. Use of the spraying immobilization technique gives rise to a response time of a few seconds, which allows sample throughputs up to 200 h-1. With a penicillin biosensor adapted in an appropriate cell detection, online measurements of penicillin V in the fermentation broth are achieved during the whole fermentation process; the results are compared with the HPLC method. Linearity, sensitivity and reproducibility of the biosensor are studied with regards to sample dilution in a stirred flow detection cell to provide optimal operating conditions. Measurements without any change in parameters are obtained during the whole fermentation process. Acetylcholinesterase sensors have been used in batch systems for the determination of pesticides, but they require large amounts of substrate. When those enzyme sensors are combined with flow injection systems, only small volumes (100 µL) of substrate are injected into the carrier stream and an automated system can be obtained for continuous control of water quality.