title: Dual closed-loop, optoelectronic, auto-oscillatory detection circuit for monitoring fluorescence lifetime-based chemical sensors and biosensors.
abstract: We present a new detection instrument for sensor measurements based on excited-state fluorescence lifetimes. This system consists of a primary optoelectronic loop containing a resonance-type rf amplifier, a modulatable fluorescence-excitation light source, a fiber optic feedback loop (with a gap for a fluorescent sensor), and a photomultiplier tube. A secondary, phase-feedback optoelectronic circuit consists of a long-wavelength-pass optical filter, a second photomultiplier tube, a photodiode, an electronic phase detector, a dc amplifier, and an electronic phase shifter (inserted into the main loop). This phase-feedback circuit is new with respect to our previous work. Under the appropriate conditions, the main loop exhibits self-oscillations, manifesting themselves as sinusoidal rf modulation of light intensity. The phase-feedback circuit detects the modulation phase shift resulting from the finite excited-state lifetimes of a fluorophore. As the excited state lifetime changes, the phase shift from the electronic phase shifter also changes, which results in a shift in self-oscillation frequency. The detection system uses self-oscillation frequency as the detection parameter and has excellent resolution with respect to changes in excited-state lifetime ( approximately 1 ps). (c) 2004 Society of Photo-Optical Instrumentation Engineers.
authors.affiliation: Center for High Technology Materials, University of New Mexico, 1313 Goddard SE, Albuquerque, NM 87106, USA.
authors.forename: Emmanuil
authors.initials: E
authors.lastname: Rabinovich
authors.forename: Tengiz
authors.initials: T
authors.lastname: Sviminoshvilli
authors.forename: Michael J
authors.initials: MJ
authors.lastname: O'Brien
authors.forename: Steven R J
authors.initials: SR
authors.lastname: Brueck
authors.forename: Gabriel P
authors.initials: GP
authors.lastname: Lopez
mesh_terms: D015374:Biosensing Techniques / Q000295:instrumentation* / Q000379:methods; D004581:Electronics; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005246:Feedback; D005452:Fluoresceins / Q000032:analysis*; D008543:Melanins; D055095:Optics and Photonics / Q000295:instrumentation*; D010860:Pigments, Biological; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013050:Spectrometry, Fluorescence / Q000295:instrumentation* / Q000379:methods*; D014159:Transducers
chemical_list: D005452:Fluoresceins; D008543:Melanins; D010860:Pigments, Biological; C030524:fluorescent age pigment; C401959:seminaphthofluorescein