Development of a fully integrated analysis system for ions based on ion-selective optodes and centrifugal microfluidics

A fully integrated, miniaturized analysis system for ions based on a centri fugal microfluidics platform and ion-selective optode membranes is describe d. The micro-fluidic architecture is composed of channels, five solution re servoirs, a measuring chamber, and a waste reservoir manufactured onto a di sk-shaped substrate of poly(methyl methacrylate). Ion-selective optode memb ranes, composed of plasticized poly(vinyl chloride) impregnated with an ion ophore, a proton chromoionophore, and a lipophilic anionic additive, were c ast, with a spin-on device, onto a support layer and then immobilized on th e 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/subs trate interactions and are controlled by the angular frequency of rotation. With this system, we have been able to deliver calibrant solutions, washin g buffers, or "test" solutions to the measuring chamber where the optode me mbrane is located. An analysis system based on a potassium-selective optode has been characterized. Results indicate that optodes immobilized on the p latform demonstrate theoretical responses in an absorbance mode of measurem ent. 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 solutions. Furthe r, the ability to measure ion concentrations by employing one standard solu tion in conjunction with acid and base and with two standards alone were st udied to delineate whether the current architecture could be simplified. Fi nally, the efficacy of incorporating washing steps into the calibration pro tocol was investigated.