Water contaminations are currently threatening ecosystems and human health on a world-wide scale. Monitoring the water quality is one of the most essential steps to provide better understanding and mitigation of water contamination. Among the water quality monitoring techniques, optofluidic technologies have created a burgeoning number of novel devices designed to test water quality in an efficient and portable format. However, current optofluidic devices have yet to be successfully translated to onsite monitoring applications due to their high cost, high maintenance and dependence on delicate laboratory instruments or bulky instruments. In this work, we developed two optofluidic platforms for onsite water quality monitoring: a fluorescence-based optofluidic platform for chemical analysis and an imaging-based optofluidic platform for microbe detection. Several technologies associated to optical sensing modules were developed to overcome the above challenges, making the optofluidic platforms compatible with onsite monitoring applications. First, excitation coupling mechanism and frequency domain time-resolved fluorescence (TRF) were developed on the fluorescence-based optofluidic platform to improve sensing sensitivity and stability, while reducing dependence on costly instruments. Their effectiveness was demonstrated by dissolved oxygen (DO) measurements and ray-tracing simulation. Second, a low-cost and portable imaging system with dual modalities were developed on the imaging-based optofluidic platform. Thus, both morphological features and fluorescent features can be observed for microbe detection without using bulky microscope setups. The effectiveness of dual-modality imaging was demonstrated by experimental results of phytoplankton analysis. Third, a fluorescence lifetime imaging (FLIM) approach was developed under a low-cost (Complementary metal–oxide–semiconductor) CMOS format. This approach enables integrating FLIM module in portable optofluidic platforms for onsite monitoring. These advances bring optofluidic platforms closer to realizing the requirements of onsite water quality monitoring and provide a clear picture for future improvements and research directions. / Thesis / Doctor of Philosophy (PhD)