Development of an optical sensor probe for the detection of dissolved carbon dioxide

A robust, low-cost optical probe for the detection of dissolved carbon dioxide has been developed. The design centres on the use of a custom-designed polymer optical element (POE), which obviates the need for optical fibres, thereby improving probe stability and rendering it more suitable for use outside a laboratory environment. The probe employs LED excitation of a luminescent sensor membrane and signal detection is provided by a silicon PIN photodiode. The phase-based sensing technique of dual luminophore referencing (DLR) was employed in conjunction with a poly(dimethylsiloxane) (PDMS) sensor membrane to yield the sensor response. The membrane was doped with the fluorescent indicator, hydroxypyrenetrisulfonic acid (HPTS) along with a reference luminophore in the form of silica microparticles, doped with the fluorescent ruthenium complex, Ru(dpp)32+. A limit of detection of approximately 7 μM of dissolved CO2 was achieved, demonstrating the promising potential of this generic sensor probe configuration.