title: A guiding light: spectroscopy on digital microfluidic devices using in-plane optical fibre waveguides.
abstract: We present a novel method for in-plane digital microfluidic spectroscopy. In this technique, a custom manifold (.stl file available online as ESM) aligns optical fibres with a digital microfluidic device, allowing optical measurements to be made in the plane of the device. Because of the greater width vs thickness of a droplet on-device, the in-plane alignment of this technique allows it to outperform the sensitivity of vertical absorbance measurements on digital microfluidic (DMF) devices by ∼14×. The new system also has greater calibration sensitivity for thymol blue measurements than the popular NanoDrop system by ∼2.5×. The improvements in absorbance sensitivity result from increased path length, as well as from additional effects likely caused by liquid lensing, in which the presence of a water droplet between optical fibres increases fibre-to-fibre transmission of light by ∼2× through refraction and internal reflection. For interrogation of dilute samples, stretching of droplets using digital microfluidic electrodes and adjustment of fibre-to-fibre gap width allows absorbance path length to be changed on-demand. We anticipate this new digital microfluidic optical fibre absorbance and fluorescence measurement system will be useful for a wide variety of analytical applications involving microvolume samples with digital microfluidics.
authors.affiliation: Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6, Canada.|Donnelly Centre for Cellular and Biomolecular Research, 160 College Street, Toronto, Ontario, M5S 3E1, Canada.|Division of Metrology for Quality of Life, Korea Research Institute of Standards and Science, Yuseong-gu, Daejeon, 305-340, Korea.
authors.forename: Kihwan
authors.initials: K
authors.lastname: Choi
authors.affiliation: Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6, Canada.
authors.forename: Jared M
authors.initials: JM
authors.lastname: Mudrik
authors.affiliation: Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6, Canada. aaron.wheeler@utoronto.ca.|Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Toronto, Ontario, M5S 3G9, Canada. aaron.wheeler@utoronto.ca.|Donnelly Centre for Cellular and Biomolecular Research, 160 College Street, Toronto, Ontario, M5S 3E1, Canada. aaron.wheeler@utoronto.ca.
authors.forename: Aaron R
authors.initials: AR
authors.lastname: Wheeler
mesh_terms: D056656:Lab-On-A-Chip Devices; D055100:Optical Fibers; D013057:Spectrum Analysis / Q000379:methods*
keywords: Absorbance; Digital microfluidics; Fibre optics; Fluorescence; Microfluidics; Optical fibres; Spectrophotometry; UV/Vis; Waveguides