On-chip integration of sequential ion-sensing system based on intermittentreagent pumping and formation of two-layer flow

A sequential ion-sensing system using a single microchip was successfully r ealized. The system developed here involves intermittent pumping of plural organic phases into a microchannel, followed by contact with a single aqueo us phase to form a stable organic-aqueous two-layer flow inside the microch annel. Because the plural organic phases created by intermittent flow conta in the same lipophilic pH indicator dye but different ion-selective neutral ionophores, different ions can be sequentially and selectively extracted i nto the different organic phases, where they can be determined by thermal l ens microscopy (TLM). We used KD-A3 as the lipophilic pH indicator dye and valinomycin and DD16C5 as neutral ionophores to demonstrate sequential ion sensing of potassium and sodium ions by measuring the deprotonated dye caus ed by the ion extraction. The integrated microfluidic system proposed here allows multi-ion sensing, which is not easily demonstrated by conventional ion sensor technology using a solvent polymeric membrane. The minimum volum e of single organic phase needed to obtain an equilibrium response without dilution by cross dispersion of two organic phases was ca. 500 nL in our sy stem, indicating that the required amounts of expensive reagents in one mea surement could be reduced to 1.7 ng and 2.8 ng for the dye and ionophore mo lecules, respectively.