Luminescent sensing systems consist of a probe molecule, a method of excitation, and a photodetector. A probe molecule for determining the concentration of carbon dioxide in a gas sample is presented. The probe molecule was prepared according to the literature and affixed to a coupon for testing in a pressure chamber. The gas composition within the chamber could be controlled allowing for the calibration of the HPTS-based probe molecule. The coupon was photoexcited with an appropriate light and the luminescent spectrum recorded with a fiber-optic spectrometer. A modified form of the Stern-Volmer equation was fit to the experimental calibration data to relate luminescent intensity to the mole fraction of carbon dioxide within the chamber. A second-order polynomial was found to fit the data with an R2 value of 0.9797. The pressure dependence of the probe molecule was determined to be less than 1% per psi. The HPTS probe molecule was shown to be photostable for about 5 hours before the luminescent intensity begins to exponentially decay. Applications of such a sensor and the necessary instrumentation to implement this technique are discussed.