Towards a gastric pH-sensor: an optrode for the pH 0–7 range

SummaryThis work describes the development of the first optical pH-sensor capable of measuring pH-values in the 0–7 range. The pH-sensitive material consists of fibrous amino-ethyl cellulose onto which fluorescein and eosin were covalently immobilised. Fluorescein was immobilised via its isothiocyanate, and immobilised eosin was obtained by bromination of the immobilised fluorescein. The material thus obtained was mechanically fixed at the end of a bifurcated optical fibre bundle. Fluorescence was excited at 490 nm and measured at >540 nm. The accuracy of the sensor is ±0.05 pH units, its response time ranges from 25 to 30 s. Practically no signal loss was observed upon constant illumination over periods of more than 15 h.

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