Monolithic integration of poly(dimethylsiloxane) waveguides and microfluidics for on-chip absorbance measurements

A monolithic integration of poly(dimethylsiloxane) (PDMS) waveguides and microfluidics is demonstrated by implementing a two-step lithographic moulding. 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. Transition and radiation losses are identified dominating along the curves whereas propagation loss increases at a steady rate of 0.249 ± 0.015 dB/cm. With the integrated system, real-time absorbance measurement of fluorescein streams yields a nearly linear response up to 250 μM and the limit of detection <50 μM.