title: Evaluation of acridine in Nafion as a fluorescence-lifetime-based pH sensor.
abstract: We report a novel fluorescence-lifetime-based pH sensing method that utilizes acridine incorporated into Nafion (AcNaf) as the fluorescent indicator. The AcNaf sensor is excited using a 380 nm light emitting diode (LED) and the fluorescence lifetimes are measured at 450 and 500 nm. The fluorescence behavior of acridine as a function of pH in aqueous phosphate buffers and incorporated into the Nafion membrane has been investigated. The results show that incorporating acridine into Nafion changes the apparent ground-state pKa from -5.45 to -9, while the apparent excited-state pKa* is only slightly changed (approximately 9.4 in 0.1 M phosphate buffer). The AcNaf film shows a good pH response with a change in average lifetime of approximately 19 ns (at an emission wavelength of 450 nm) over the pH 8 to 10 range. We also show that excited-state protonation does not occur in the AcNaf sensor film and that chloride quenching cannot occur because of the permselective nature of Nafion. We also discuss how the unique structure of Nafion affects the fluorescence behavior of acridine at various pH values and examine the impact of buffer concentration on apparent pKa and pH sensing ability.
authors: Department of Physics, National University of Ireland-Galway, Galway, Ireland.
authors: Alan G
authors: AG
authors: Ryder
authors: Sarah
authors: S
authors: Power
authors: Thomas J
authors: TJ
authors: Glynn
mesh_terms: D000166:Acridines / Q000737:chemistry*; D001672:Biocompatible Materials / Q000138:chemical synthesis / Q000737:chemistry*; D015374:Biosensing Techniques; D005465:Fluorocarbon Polymers / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D046911:Macromolecular Substances; D008422:Materials Testing; D008567:Membranes, Artificial; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013050:Spectrometry, Fluorescence / Q000295:instrumentation / Q000379:methods*; D013997:Time Factors
chemical_list: D000166:Acridines; D001672:Biocompatible Materials; D005465:Fluorocarbon Polymers; D046911:Macromolecular Substances; D008567:Membranes, Artificial; C040402:perfluorosulfonic acid