Low-cost device for ratiometric fluorescence measurements

An all-solid-state, low-cost device for fluorescent wavelength-ratiometric detection is described. Ultrabright light-emitting diodes were used as ligh t sources. This allowed electronic modulation of the light, simple optical configuration, and miniaturization of the instrument. Narrow-bandpass inter ference filters were used for wavelength separation. Detection was accompli shed by high-sensitivity, large-surface PIN photodiodes. An integrating dou ble-ramp technique with fixed upper and lower thresholds was employed for c onversion of the light intensities into time intervals. The duty ratio of t he output signal was a function of the fluorescence intensity ratio. Additi onally, the concentration of the fluorophore could be measured. The device could be easily designed as a battery-operated version. It could be used fo r a variety of ratiometric fluorescence measurements. (C) 1999 American Ins titute of Physics. [S0034-6748(99)01412-4].