Poly(dimethylsiloxane) Waveguides Integrated with Microfluidics for Absorbance Measurement

The monolithic integration of poly(dimethylsiloxane) (PDMS) waveguides with microfluidics is presented. Silicone oil is added in PDMS precursor to tune the refractive index of waveguides with air as the side and top cladding layer. Curved and straight waveguides are characterized for their insertion loss mainly due to propagation, radiation, and transition. For the integrated system, real-time absorbance measurement of fluorescein streams yields a linear response 250 muM and with a limit of detection <50 muM. The amount of stray light has been reduced with the 90deg curved waveguide configuration and shows a two-fold increase of sensitivity in the absorbance measurement as compared with straight waveguides configuration.