A solid-state instrument for fluorescence chemical sensors using a blue light-emitting diode of high intensity

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Abstract
A recently introduced blue light-emitting diode with high intensity is used as radiation source for chemical sensor membranes employing fluorescence changes. An inexpensive plastic fibre coupler guides the light from the source to the membrane and the fluorescence back to the detector. Photodiodes are employed for this purpose and dye filters for wavelength discrimination. Lock-in amplification for elimination of ambient light interference is carried out with a single integrated circuit. Applications are demonstrated with sensing membranes for oxygen and carbon dioxide.