title: High speed low noise multiplexed three color absorbance photometry.
abstract: Multispectral photometry is often required to distinguish samples in flow injection analysis and flow cytometry; however, the cost of multiple light detectors, filters, and optical paths contribute to the high cost of multicolor and spectral detection systems. This paper describes frequency division multiplexing (FDM), a simple approach for performing multi-wavelength absorbance photometry with a single light detector and a single interrogation window. In previous efforts, modulation frequencies were <10 KHz, resulting in a detector bandwidth of <20 Hz. This paper presents a high frequency FDM circuit which can increase the oscillation frequencies to several 100 KHz, improving the detection bandwidth by a factor of 10 while still maintaining low cost. Light from 3 different LED sources are encoded into unique frequency channels, passed through the detection cell, and later demodulated using phase-sensitive electronics. Electronic multiplexing couples all light sources into a single optical train without spectral filters. Theory and high frequency considerations are demonstrated. Simultaneous three color absorbance detection is demonstrated in solutions and in flowing droplet microreactors. This technique can potentially reduce the cost of multicolor photometry by replacing expensive optical components with low-cost electronics.
authors.affiliation: Electrical and Computer Engineering Department, Wayne State University, Detroit, MI 48202, USA. k_kadesh@wayne.edu
authors.forename: Khaled M
authors.initials: KM
authors.lastname: Dadesh
authors.forename: G K
authors.initials: GK
authors.lastname: Kurup
authors.forename: Amar S
authors.initials: AS
authors.lastname: Basu
mesh_terms: D000042:Absorption; D015374:Biosensing Techniques / Q000295:instrumentation*; D003116:Color; D003124:Colorimetry / Q000295:instrumentation*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D017022:Flow Injection Analysis / Q000295:instrumentation*; D008027:Light; D010783:Photometry / Q000295:instrumentation*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D059629:Signal-To-Noise Ratio; D018511:Systems Integration