Sensors based on a single sample-donor stream

1 Sensors based on a single sample-donor stream 

In this type of sensor (Fig. 5.4.A), the sensing microzone accommodating the gas-diffiision membrane is traversed by a stream of (a) a carrier intended to transport the injected sample, condition it (e.g. adjusting its pH) and prepare/regenerate the sensor or b) the sample itself, introduced into the continuous manifold by aspiration or injection and subsequently mixed in a continuous fashion with another stream if needed. 

The flow injection manifold shown in Fig. 5.5.A, which includes a probe-type fluorimetric biosensor accommodated in a thermostated flow-cell at 35°C, was used for the determination of L-glutamate in foods and 

The carrier used for this purpose consisted of a 0.1 M phosphate buffer of pH 7. The appearance of the sensing microzone is shown in Fig. 5.5.B. The oxygen optrode used was based on a 10-pm silicone rubber film containing dissolved decacyclene as indicator (S) that was fixed on a 110-pm thick polyester support (PS). A 9-pm black PTFE membrane (I) was used for optical insulation. The dye fluorescence was found to be markedly dependent on the concentration of oxygen, which exerted a quenching effect on it. The enzyme (glutamate oxidase) was immobilized on a 150-pm thick immunoaffmity membrane (E). The sensor was prepared similarly as reported by Trettnak et al. [7]. 

The other above-mentioned sensing system relies on measurement of carbon dioxide (rather than oxygen) produced in the biochemical reaction of L-glutamate catalysed by glutamate decarboxylase (GDC)  

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