Sensors, with renewable surfaces

The paper will review past and present efforts to miniaturize flow injection systems, will discuss the principles of sequential injection and its advantages for micromimatunzation New type of detector - the jet ring cell will be introduced and its use in cytoanalysis and for flow injection on renewable surfaces will be demonstrated Merits of novel class of chemical sensors with renewable surfaces will be discussed... 

The combination of chemical and biological sensors with flow injection has been demonstrated. Both more-traditional-type sensors such as pH electrodes and newer sensors such as fiber optics and surface acoustic wave detectors have been incorporated into FIA systems with success. An advantage that FIA brings to the sensor field is the possibility of turning a moderately selective sensor into a selective sensor by incorporating into the FIA system some type of selectivity enhancement technique such as gas diffusion, dialysis, and reactors. Finally the FIA systems permit renewable systems since sensor surfaces and reaction cells can be washed, surface regenerated, and reagents replenished on demand. 

Most biosensors based on AChE have the enzymes immobilized on the surface of the sensor. The inhibition reaction being irreversible, the membrane with immobilized enzyme has to be replaced after several measurements or the biosensor can be use for only one determination. Due to this fact, the researchers tried to realize pesticide biosensors with a renewable surface or disposable biosensors based on screen-printed electrodes (SPE). The screen-printing technology provides a simple, fast and inexpensive method for mass production of disposable biosensors for different biomolecules starting with glucose, lactate and finishing with environmental contaminants as pesticides (Kulys et al., 1991) and herbicides (Skladal, 1992). 

Ruedas Rama, M. J. Ruiz Medina, A. Molina Diaz, A. A flow-injection renewable surface sensor for the fluorometric determination of vanadium (V) with Alizarin Red S. Talanta 2005, 66, 1333-1339. Macdonald, J. G. Huang, Y. Yang, K. Kim, J. Wei, N. Single phase color change agents for liquid detergents for cleaning surfaces. U.S. Pat. Appl. Publ. US 2005049157, 2005 Chem, Abstr. 2005,142, 263578. 

M.J. Ruedas Rama, A. Ruiz Medina, and A. Molina Diaz. A flow-injection renewable surface sensor for the fluorimetric determination of vanadium(V) with Alizarin Red S. Talanta 66 ... 

ELECTROCHEMICAL SENSORS AND DETECTORS WITH RENEWABLE ELECTRODE SURFACES... 

Electrochemical Sensors and Detectors with Renewable Electrode Surfaces Jifi Tenygl... 

The behavior of potentiometric and pulsed galvanostatic polyion sensors can be directly compared. Figure 4.11 shows the time trace for the resulting protamine calibration curve in 0.1 M NaCl, obtained with this method (a) and with a potentiometric protamine membrane electrode (b) analogous to that described in [42, 43], Because of the effective renewal of the electrode surface between measuring pulses, the polyion response in (a) is free of any potential drift, and the signal fully returns to baseline after the calibration run. In contrast, the response of the potentiometric protamine electrode (b) exhibits very strong potential drifts. 

Detection of Li+ in artificial serum with a voltammetric Li-selective electrode in a flowthrough system was demonstrated [64], Lithium salts such as lithium carbonate have been extensively used for treatment of manic depressive and hyperthyroidism disorders. The therapeutic range of Li concentration is generally accepted to be 0.5-1.5mM in blood serum. The authors used normal pulse voltammetry in which a stripping potential was applied between pulses in order to renew the membrane surface and expel all of the extracted ions from the membrane, similar to galvanostatically controlled potentiometric sensors described above. Unfortunately, the insufficient selectivity... 

However, all these sensors suffer from the very slow kinetics of the dissociation of the complexes. Thus renewal of the transducer surface for repeated measurements with the same device is very difficult. Dissociation of the complexes can be attained by applying highly concentrated urea solutions to the sensor, but even then not more than a few measurements are possible with the same device, as has been shown with a sensor for Salmonella typhimurium [236]. As a consequence, the application of immunological reactions for these and other transducer surfaces is in general limited to one-shot measurements. On the other hand, as antibodies can be obtained against nearly any substance, affinity sensors, mainly those based on piezoelectric crystals, offer so many possibilities that their further development is a promising challenge. 

The development of potentiometric detectors based on ion-selective electrodes continues to expand the scope of clinical and pharmaceutical applications of FIA. The small surface area of the sensor avoids adsorption problems and extends the service life of the electrode. The surface can be readily renewed periodically by alternating the washing cycles with the sampling cycles. The selectivity thus achieved is usually very good as it relies on differences in the... 

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