title: Characterisation of spatial and temporal changes in pH gradients in microfluidic channels using optically trapped fluorescent sensors.
abstract: This paper demonstrates the use of micron sized beads, modified with fluorescent dyes, as non-invasive sensors to probe the local changes in pH, within a microfluidic channel. To achieve this, amine modified polystyrene spheres (either 3 microm or 6 microm in diameter) were functionalised with the pH sensitive fluorochrome SNARF-1 to produce point sensors. The modified beads were trapped at defined positions close to a pair of integrated planar gold microelectrodes within the channel, using optical tweezers. Both transient and steady-state electrochemical potentials were applied to the microelectrode pair in order to generate changes in the local pH, associated with electrolysis. The functionalised beads indicated the pH changes in the channel, measured as a change in the fluorescence signal, generated by the immobilised pH sensitive dye. Responses were measured with temporal resolutions of between 1 and 200 ms, whilst the spatial resolution of the pH gradients was limited by the size of the beads to 3 microm.
authors.affiliation: Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, UK.
authors.forename: Norbert
authors.initials: N
authors.lastname: Klauke
authors.forename: Paul
authors.initials: P
authors.lastname: Monaghan
authors.forename: Gavin
authors.initials: G
authors.lastname: Sinclair
authors.forename: Miles
authors.initials: M
authors.lastname: Padgett
authors.forename: Jon
authors.initials: J
authors.lastname: Cooper
mesh_terms: D001578:Benzopyrans / Q000737:chemistry*; D004563:Electrochemistry / Q000379:methods; D005456:Fluorescent Dyes / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008839:Microelectrodes; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation / Q000379:methods*; D009284:Naphthols / Q000737:chemistry*; D055095:Optics and Photonics / Q000295:instrumentation*; D011137:Polystyrenes / Q000737:chemistry; D012235:Rhodamines / Q000737:chemistry*
chemical_list: D001578:Benzopyrans; D005456:Fluorescent Dyes; D009284:Naphthols; D011137:Polystyrenes; D012235:Rhodamines; C091666:seminaphthorhodaminefluoride