On-chip absorption measurements using an integrated waveguide

Abstract

Square hollow waveguides are used to integrate measurement of absorption with chip-based electrophoresis. The 50x50 microm liquid channel and 50x50 microm waveguide are etched as a negative pattern into a silicon master and replicated as a positive in poly-dimethylsiloxane (PDMS). The uniform refractive index of the chip prevents guiding by total internal reflection. Instead, light at 488 nm is guided by reflection at the air-PDMS interface. The waveguide has a 60% efficiency over a distance of 3.2 cm. Separation of fluorescein and the dye BODIPY is demonstrated. A detection limit (S/N=3) of 200 microM fluorescein is obtained using a 50 microm pathlength and a simple photocell detector.

Sensitivity enhancement for colorimetric glucose assays on whole blood by on-chip beam-guidance

“…In miniaturized formats, the sensitivity suffers from the significantly reduced optical path lengths compared to macroscopic setups. To extend the path length for a typically perpendicular incidence of a probe beam, optical waveguides (Verpoorte et al, 1992;Splawn and Lytle, 2002), microlenses (Roulet et al, 2001), or optical fibers (Liang et al, 1996;Petersen et al, 2002) are integrated on flat microfluidic chips accommodating low-aspect-ratio detection cells (Walt, 2000). However, these approaches require rather complex chip designs and an elaborate, high-accuracy alignment of the optical components.…”

Integrated microfluidic biophotonic chip for laser induced fluorescence detection

“…Even though monolithic fabrication of the waveguides with the microfluidic channels is feasible (Lien et al 2003;Cohen et al 2004;Friis et al 2001;Leeds et al 2004), optical losses (Splawn and Lytle 2002) incurred in the systems due to scattering, insertion and surface roughness would be detrimental for the detection of low concentration of biomolecules. Therefore, for the present application, the fibers were directly integrated with the microfluidic chip in order to improve the performance of the hybrid integrated system.…”

Low-dispersion electrokinetic flows for expanded separation channels in microfluidic systems:

“…The delivery of light to chip-based systems using waveguides and optical fibers has been the subject of numerous investigations [25,[36][37][38][39][40][41][42][43][44][45][46][47][48][49][50]. As light delivery and collection from chip-based detectors become routine, channel designs that optimize the delivery of samples for optical detection will be an important feature.…”