EXPERIMENTAL VERIFICATION OF ION TRANSPORT MECHANISM BY ION CONCENTRATION POLARIZATION AND ITS APPLICATIONS

Abstract

As the ion concentration polarization (ICP) phenomenon has been intensively researched for a decade, the unprecedented demand for the complete picture of ions and analytes distributions near the nanoporous membrane has been strongly arisen not only for fundamental nano-electrokinetic studies but also for engineering applications. While micro/nanofluidic platform has been generally adopted in such research fields, the low throughput (<nL/min) would hinder the direct concentration measurement near the membrane. In this work, firstly, we suggested a direct concentration profiling method

instead of time-consuming sample collection, the concentration changes of the prefilled sample in each reservoir were measured. We experimentally metered the individual ion concentrations near the nanoporous membrane and succeeded for precise elucidation on the previously reported ICP purification and preconcentration mechanisms. As a result, ion distributions caused by ICP were classified with 3 regions

one for outside the ion depletion zone (IDZ) at the anodic side, and the other for inside the IDZ at the anodic side where, and the last one for the ion enrichment zone (IEZ) at the cathodic side. Firstly, we discovered that analytes larger than the size of nanopore were completely repelled by the ICP layer, while most of salts were removed from the analyte stream because most of cations were transported through the nanoporous membrane to sustain ICP phenomenon, and most of anions were consumed by electrode reaction for electro-neutrality requirement at the outside IDZ. These combined effects would provide a versatile process named as desalted analyte preconcentration which enables the perfect recovery of target analyte and simultaneously, the removal of unnecessary salts. Secondly, we discovered the concentration inversion of lithium and sodium ion inside the IDZ. Since the induced electric field inside the IDZ was highly amplified up to 100,000 V/m scale, hydrated ions in a water solution would be dehydrated so that mobility inversion of lithium and sodium ion occurred. Finally, we confirmed that the 65 % of cation transportation through the nanoporous membrane occurred, so the concentration amplification ratio would be controlled at the IEZ as well as the concentration depending on the mobility of the individual ions. Based on the results analyzed above, we proposed two applications: a lossless regenerative ink manufacturing device and a portable continuous purification device for artificial kidney development. Firstly, as the novel concept of ink recycler, we showed that salt ions which causes serious deterioration of inkjet head were desalted (~40 %) and ink molecules were preconcentrated (~200 %) in a single step operation. Therefore, the presenting demonstration based on suggested profiling would be a key operational mechanism of various refinery industry such as drug discovery and chemical industry. Secondly, by utilizing ion transport mechanism near nanoporous membrane, the ICP purifier, for the first time, was applied for a novel continuous peritoneal dialysate recycler. Most of charged hazardous substances were sufficiently removed by conventional ICP mechanisms. Moreover, slightly charged toxic molecule (creatinine) was mostly eliminated through nanoporous membrane, and uncharged toxic molecule (urea) was perfectly decomposed by electrochemical reactions. Based on the combined removal mechanisms confirmed in a micro/nanofluidic platform, for practical applicability, a macro ICP device with 100,000 times increase in water treatment capacity from 0.1 μL/min to 10 mL/min was newly introduced. As a results, we showed that the blood toxin concentration was reduced up to 10 % at the in-vivo test with 4 hours continuous operation. We would expect significant advances in a quality of life for chronic kidney disease patients by this ICP purifier as a portable dialysate recycler.