Low-Cost Ratiometric Fluorescence Sensors for Accurate Detection of pH Value

摘要

Fluorometric sensing is a major optical measurement approach widely used in chemical,udbiological, and medical fields. In conventional fluorescence measurements, two approaches haveudbeen used to build low-cost fluorescence sensors. The first approach is to use CCD detector arrays,udwhich incur low sensitivity. The second approach is to use a narrow bandpass filter, which incurudlow selectivity.udIn this thesis, a low-cost ratiometric fluorescence sensor was developed to achieve high sensitivityudand high selectivity simultaneously. Two highly sensitive photodetectors were used to monitorudfluorescence signal excited by two ultraviolet LEDs with different emitting wavelengths to achieveudthe sensitivity close to single photon counting. The ratio of fluorescence signals excited by twoudLEDs was used to identify targeted species with improved selectivity.udThis thesis describe the design, development, implementation of optical components, mechanicudhousing, digital and analog circuits that enable the ratiometric fluorescence measurements. Theudapplications and functionalities of the sensor was demonstrated to measure pH values in liquidudsolution. The low-cost sensing systems can be programmed in stand-alone operation or beudcontrolled by a laptop or a cellular devices for a wide spread applications including water qualityudmonitoring, biological sensing, and chemical processing monitoring.