Abstract: An optical sensor for nitric oxide (NO) is described. The sensor involves a flow injection analysis (FIA) system coupled with an evanescent wave (EW) sensor employing total internal reflection of fluorescence radiation (TIRF). The detection is based on the measurement of the decrease in fluorescence response in the presence of NO of a highly fluorescent product which is the complex of glutathione and 7-diethylamino-3-(4'-maleimidylphenyl)-4-methylcoumarin (CPM). CPM forms a highly fluorescent product with thiol containing compound i.e. cysteine/glutathione which can be detected using an evanescent fluorosensor. NO form a stable complex with glutathione/cysteine which then does not react with CPM to form fluorescent product. Thus there is a decrease in the fluorescence signal on increasing concentration. of NO with constant concentration. of glutathione. An excellent FIA response was observed on the injection of the constant concentration. of CPM-glutathione product obtained by treating constant concentration. of glutathione with varying concentration. of NO. The lowest detection limit of NO is found to the order of 0.10 µM.

Abstract: FIA systems for the determination of sucrose are described in which (i) invertase and µarotase were immobilized on to controlled pore glass beads in an enzyme reactor and the C-paste detection electrode was modified with glucose oxidase (I) and tetracyanoquinodimethane (II) as electron transfer mediator or (ii) invertase was incorporated into the C-paste electrode together with I and II (an enzyme reactor was not used). Both systems were operated with 0.1 M phosphate buffer of pH 7 as the carrier stream (30 ml/h) and a 250 µL sample loop. The amperometric response was measured at 200 mV vs. Ag/AgCl. The detection range was 0.025-200 mM for i and up to 2 M for ii.

Abstract: A flow injection analysis (FIA) sensor for the oxidation of NADH is reported. The system utilizes a graphite paste electrode modified with the electroactive material tetracyanoquinodimethane (TCNQ). TCNQ acts as an efficient mediator for the oxidation of NADH to biologically active NAD+. Alcohol dehydrogenase/lactate dehydrogenase and NAD+ were coimmobilized in TCNQ-modified graphite paste using polyethylenimine to develop a FIA sensor for ethanol/lactate. The system responded rapidly with wide linearity. Response curves for ethanol/lactate and NADH are reported.