[Show abstract][Hide abstract] ABSTRACT: Fluorescence detection is one of the most widely used techniques for measuring analyte concentration in biological applications. Although used frequently with bulk systems, there are important considerations in using this approach in thin (<100 μm) microfluidic lab-on-a-chip (LOC) systems in relating the measured fluorescence signal to analyte concentration. In this work, a general relationship between the photoresponse of an on-chip organic photodetector (OPD) and concentration of a fluorescent dye Rhodamine 6G in a microfluidic chip is presented. The developed theoretical model for photoresponse matches well to the extreme sub-linearity observed in measurements in a dilution series from 10 nM to 1 mM. The influence of the system factors, such as noise, detector sensitivity, and optical power were also analyzed to indicate design changes to improve the system performance and limits of detection even further.
Journal of Luminescence 01/2010; · 2.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report a high-sensitivity, disposable lab-on-a-chip with a thin-film organic light-emitting diode (OLED) excitation source and an organic photodiode (OPD) detector for on-chip fluorescence analysis. A NPB/Alq3 thin-film green OLED with an active area of 0.1 cm(2) was used as the excitation source, while a CuPC/C(60) thin-film OPD with 0.6 cm(2) active area was used as a photodetector. A novel cost-effective, cross-polarization scheme was used to filter out excitation light from a fluorescent dye emission spectrum. The excitation light from the OLED was linearly polarized and used to illuminate a microfluidic device containing a 1 microL volume of dye dissolved in ethanol. The detector was shielded by a second polarizer, oriented orthogonally to the excitation light, thus reducing the photocurrent due to excitation light leakage on the detector by approximately 25 dB. The fluorescence emission light, which is randomly polarized, is only attenuated by approximately 3 dB. Fluorescence signals from Rhodamine 6G (peak emission wavelength of 570 nm) and fluorescein (peak emission wavelength of 494 nm) dyes were measured in a dilution series in the microfluidic device with emission signals detected by the OPD. A limit-of-detection of 100 nM was demonstrated for Rhodamine 6G, and 10 microM for fluorescein. This suggests that an integrated microfluidic device, with an organic photodiode and LED excitation source and integrated polarizers, can be fabricated to realize a compact and economical lab-on-a-chip for point-of-care fluorescence assays.
Lab on a Chip 06/2008; 8(5):794-800. · 5.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The trend in medical equipment is toward compact and integrated low cost medical test devices. Fluorescence-based assays are used to identify specific pathogens through the presence of dyes, but typically require specialized microscopes and narrow-band optical filters to extract information. We present a novel method of using polarizers in cross orientation with each other to filter out excitation light and allow detection of low signal levels of fluorescence with a simple intensity-based detector in the presence of high levels of excitation light. This concept is demonstrated using an inverted microscope fitted with a halogen lamp as the excitation source and an organic photovoltaic (PV) cell as the intensity detector. The excitation light is linearly polarized and used to illuminate a microfluidic device containing a 50µl volume of Rhodamine 6G dye dissolved in water. The detector (with a second polarizer orientated perpendicularly to the first) is placed over the microfluidic device. The resulting emission signal was detected by the organic PV cell down to a concentration of 100 nM This suggests that an integrated microfluidic device, with a PV detector and an organic light emitting excitation source and integrated polarizers, could be fabricated to realize a economical "lab on a chip" device for fluorescence assays.