| Abstract
| - A sequential ion-sensing system using a single microchipwas successfully realized. The system developed hereinvolves intermittent pumping of plural organic phasesinto a microchannel, followed by contact with a singleaqueous phase to form a stable organic−aqueous two-layer flow inside the microchannel. Because the pluralorganic phases created by intermittent flow contain thesame lipophilic pH indicator dye but different ion-selectiveneutral ionophores, different ions can be sequentially andselectively extracted into the different organic phases,where they can be determined by thermal lens microscopy(TLM). We used KD-A3 as the lipophilic pH indicator dyeand valinomycin and DD16C5 as neutral ionophores todemonstrate sequential ion sensing of potassium andsodium ions by measuring the deprotonated dye causedby the ion extraction. The integrated microfluidic systemproposed here allows multi-ion sensing, which is noteasily demonstrated by conventional ion sensor technology using a solvent polymeric membrane. The minimumvolume of single organic phase needed to obtain anequilibrium response without dilution by cross dispersionof two organic phases was ca. 500 nL in our system,indicating that the required amounts of expensive reagentsin one measurement could be reduced to 1.7 ng and 2.8ng for the dye and ionophore molecules, respectively.
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