Microfluidics offers a powerful platform for both uncovering complex fluid behavior and advancing rapid biosensing technologies. This talk highlights recent developments ranging from viscoelastic flow instabilities to precision diagnostics. Using selective laser-induced etching, we create robust three-dimensional glass microchannels for high-resolution visualization of nonlinear flow phenomena, including elastic turbulence and symmetry breaking. I will also present microfluidic biosensing platforms for rapid detection of COVID-19 antibodies, cancer biomarkers, and bacteria, demonstrating how microfluidics can bridge fundamental fluid mechanics and translational healthcare applications.