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Schematic of a pJFET microfluidic chip. A pair of oppositely facing polyelectrolytes, pDADMAC, and pAMPSA, is positioned on the microchannel wall. The cross section of each polyelectrolyte has a depth of and a width of . Cations and anions in the microchannel are extracted locally by applying the gate voltage through these charge-selective polyelectrolytes. The gate voltage is applied across two different polyelectrolytes and the source-drain current flowing between the inlet and outlet of the mainchannel is measured.
Mechanism underlying the control of ionic flow and fluorescence images of the fluorescein and the rhodamine 6G for tracking the movement of the anions and cations by adjusting the gate voltage in the system. (a) When the gate voltage is not applied, cations and anions are equally distributed in the microchannel. The fluorescein (anionic dye) and the rhodamine 6G (cationic dye) are diffused into the positively charged pDADMAC and negatively charged pAMPSA, respectively. (b) When a gate voltage is applied, fluorescein and rhodamine 6G are rapidly extracted from the microchannel, and the ion concentration between the polyelectrolytes decreases. (c) As the gate voltage is increased, an ion depletion region appears in the middle of the mainchannel and subsequently expands.
Output characteristics of a pJFET. The source-drain current, , is directly related to the ion depletion region formed by the gate voltage. When the gate voltage is increased from 0 to 6 V, decreased because of the large ion depletion region, which reduces the conductivity of the microchannel. Each point is tested five times.
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