Cavity-enhanced optical methods for online microfluidic analysis

► Absorption spectroscopy is a potentially useful detection technique for microfluidic applications. ► Conventional single pass measurements are hampered by the short pathlengths encountered on microfluidic chips. ► Extended pathlength single pass methods, multi-pass methods, and cavity-enhanced methods offer strategies for increasing the pathlength and improving detection sensitivity. ► Cavity-enhanced methods in particular offer improved detection sensitivity while maintaining a small probed volume.