On-chip absorption and fluorescence spectroscopy with polydimethylsiloxane (PDMS) microfluidic flow channels

We describe a system, which integrates PDMS microfluidic flow channels, a CMOS active pixel sensor (APS) imager, and commercial light sources for performing visible absorption and fluorescence spectroscopy. PDMS elastomer allows for spectroscopic measurements to be performed in the visible (350 to 750 nm) wavelength range. Along with a sensitive silicon photodetector such as an APS imager, measurements can be made on low concentrations of solutions by placing the microfluidic flow channels directly on the imager. Emission sources for absorption measurements are typically commercial LEDs with peak emission wavelengths that match the peak absorption wavelengths of the material under test. For calibration purposes, known dyes are tested and compared with the results obtained from the imager. Fluorescence measurements are performed in much the same way, but a band-blocking filter is placed between the microfluidic channels and the imager to greatly attenuate the pump wavelength. Typical emission sources for fluorescence are commercial Ar ion lasers and semiconductor lasers. We feel that the system has great advantages due to its miniaturized size and small fluid volumes required. Further system miniaturization is also possible due to the integration of emission sources and the expandability of CMOS imagers to integrate on board image processing