Development of a Fully Integrated Analysis System for Ions Based on Ion-Selective Optodes and Centrifugal Microfluidics R. Daniel Johnson, Ibrahim H. A. Badr, ² Gary Barrett, Siyi Lai, ‡ Yumin Lu, § Marc J. Madou, § and Leonidas G. Bachas* Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055 A fully integrated, miniaturized analysis system for ions based on a centrifugal microfluidics platform and ion- selective optode membranes is described. The micro- fluidic architecture is composed of channels, five solution reservoirs, a measuring chamber, and a waste reservoir manufactured onto a disk-shaped substrate of poly(methyl methacrylate). Ion-selective optode membranes, com- posed of plasticized poly(vinyl chloride) impregnated with an ionophore, a proton chromoionophore, and a lipophilic anionic additive, were cast, with a spin-on device, onto a support layer and then immobilized on the disk. Fluid propulsion is achieved by the centrifugal force that results from spinning the disk, while a system of valves is built onto the disk to control flow. These valves operate based on fluid properties and fluid/ substrate interactions and are controlled by the angular frequency of rotation. With this system, we have been able to deliver calibrant solutions, washing buffers, or “test” solutions to the measuring chamber where the optode membrane is located. An analysis system based on a potassium-selec- tive optode has been characterized. Results indicate that optodes immobilized on the platform demonstrate theo- retical responses in an absorbance mode of measurement. Samples of unknown concentration can be quantified to within 3 % error by fitting the response function for a given optode membrane using an acid (for measuring the signal for a fully protonated chromoionophore), a base (for fully deprotonated chromoionophore), and two standard solu- tions. Further, the ability to measure ion concentrations by employing one standard solution in conjunction with acid and base and with two standards alone were studied to delineate whether the current architecture could be simplified. Finally, the efficacy of incorporating washing steps into the calibration protocol was investigated. Recent trends in analytical chemistry have been toward the development of miniaturized measurement devices as embodied in micro-total analysis systems ( μ-TAS) or microelectromechanical systems (MEMS). Such systems usually consist of a microdimen- sioned architecture of reservoirs and channels formed in a substrate material (or “chip”) by a variety of microfabrication techniques; 1,2 fluid manipulation through the architecture is achieved by some type of microfluidic pumping mechanism. The drive to produce these devices lay primarily in a number of inherent advantages including low power and space requirements, minimal reagent and sample consumption, shortened analysis times, and disposability. 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