Integrated polymer waveguides for absorbance detection in chemical analysis systems

A chemical analysis system for absorbance detection with integrated polymer waveguides is reported for the first time. The fabrication procedure relies on structuring of a single layer of the photoresist SU-8, so both the microfluidic channel network and the optical components, which include planar waveguides and fiber-to-waveguide coupler structures, are defined in the same processing step. This results in self-alignment of all components and enables a fabrication and packaging time of only one day. The fabrication scheme has recently been presented elsewhere for fluorescence excitation of beads. The emphasis of this paper is on the signal-to-noise ratio of the detection and its relation to the sensitivity. Two absorbance cells with an optical path length of 100 /spl mu/m and 1000 /spl mu/m were characterized and compared in terms of sensitivity, limit of detection and effective path length for measurements of the dye Bromothymol Blue. The influence of three different bonding procedures on the spectrally resolved propagation loss of the integrated waveguides between 500 nm and 900 nm was furthermore determined.