Research ArticleAPPLIED SCIENCES AND ENGINEERING

Chemical delivery array with millisecond neurotransmitter release

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Science Advances  02 Nov 2016:
Vol. 2, no. 11, e1601340
DOI: 10.1126/sciadv.1601340
  • Fig. 1 Architecture of device and ionic currents.

    (A) Side view of a device showing the three electrolytes (source, target, and waste) with their potentials set by the electrodes to VS, VT = 0, and VW, respectively. The VCE is set to positive values to switch delivery on and to negative values to switch delivery off, with respect to the grounded VT. The dark gray material illustrates the cation-selective polyanion, which is the pathway for cations from the source to the waste; the PEDOT:PSS control electrode is depicted in blue, and the anion-selective polycation is depicted in red. In general, a positively charged material is depicted in red, and a negatively charged material is depicted in gray or blue. The encapsulation material is shown in yellow. (B) Cationic and anionic currents when delivery is on. (C) Ionic currents when delivery is off. (D) Ions accumulate at the internal interface of the BM when delivery is on and when the BM diode is in forward bias. (E) Reverse-bias of the BM diode leads to ion depletion in the BM interface, which limits the currents. (F) Top view of array comprising six of the structures in (A) in parallel. Arrows point to six delivery points in a common target electrolyte.

  • Fig. 2 Characterization of ion delivery.

    (A) Typical currents when delivering acetylcholine during a 2-s-long pulse [VCE, VS, and VW = −0.2 V (<0 and >2 s)/+0.7 V (0 to 2 s), +7 V, and −7 V]. (B) Protons were loaded into the source, and the pH indicator was added to the target and the waste. A potential between source and waste was applied. With the BM diode reverse-biased (VCE = −0.4 V with respect to VT), no color change indicating proton delivery was observed in the target (top). With the BM diode in forward bias (VCE = +0.7 V), a red cloud appeared at the delivery point (arrow, bottom). (C) Delivery current versus time for 60-ms-long delivery pulses of acetylcholine (VCE = −0.2 V/+0.7 V). (D) Measured amount of acetylcholine in the target after 1000 s of delivery with pulse lengths varying from 2 to 1000 ms, using a 20% duty cycle. The inset is a close-up of pulse lengths up to 200 ms, with logarithmic time scale. (E) Protons could be delivered separately from all six pixels in the array (Figs. 1F and 3E). Images show the color-adjusted pH response (profile shown as white line). Each row is a separate image, where delivery was on in pixel 1 on row 1, pixel 2 on row 2, etc. Delivery is only apparent in the addressed pixels, which suggests low leakage from the reverse-biased pixels. The original color image can be seen in fig. S5.

  • Fig. 3 Transport and switching mechanism.

    (A) Schematic side view of the device showing two hypothetical paths for cations. The polyanionic channel is depicted in dark gray, the PEDOT:PSS electrode is depicted in blue, and the polycationic layer is depicted in red. (B) Potential profile experienced by a cation following path 1 and (C) potential profile experienced by a cation following path 2. Both (B) and (C) illustrate the potential when the PEDOT:PSS control electrode has just been switched on (dashed line) and when delivery is statically off (solid line). The potential in the PEDOT:PSS is raised above zero by the control electrode when delivery is on (VCE = +0.7 V) but lower when delivery is off, which explains why delivery should only occur from the positively biased control electrodes.

  • Fig. 4 Simplified equivalent circuit.

    (A) Equivalent circuit describing the dynamic ion discharge from the PEDOT:PSS when delivery is switched on. BM diode is modeled as a capacitor and a diode in parallel, CBM and RBM, whereas the PEDOT:PSS is modeled as a capacitor. (B) Array circuit overlaid over an image of the actual array. Blue arrowheads indicate the delivery currents from each delivery point. In the underlying image, only VCE 2 has been addressed to deliver protons.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/11/e1601340/DC1

    Permselectivity of PEDOT:PSS

    Prevention of passive leakage

    Simple model of delivery

    Equivalent circuit modeling

    fig. S1. Delivery of H+ from a 1-mm × 1-mm large control electrode, with a 20-μm hole.

    fig. S2. Suppression of diffusive leakage of acetylcholine by reverse-biasing the control electrode.

    fig. S3. Fit of delivery data to determine maximum dynamics (same data as Fig. 2D).

    fig. S4. Delivery currents for various pulse length τ.

    fig. S5. Original images showing how one delivery site in each image has been addressed.

    fig. S6. Image of an array with biologically relevant pixel spacing (200-μm spacing between pixels).

    fig. S7. Simulated 5-s delivery pulses using simple circuit model.

    Movie S1

    Reference (25)

  • Supplementary Materials

    This PDF file includes:

    • Permselectivity of PEDOT:PSS
    • Prevention of passive leakage
    • Simple model of delivery
    • Equivalent circuit modeling
    • fig. S1. Delivery of H+ from a 1-mm × 1-mm large control electrode, with a 20-μm hole.
    • fig. S2. Suppression of diffusive leakage of acetylcholine by reverse-biasing the control electrode.
    • fig. S3. Fit of delivery data to determine maximum dynamics (same data as Fig. 2D).
    • fig. S4. Delivery currents for various pulse length τ.
    • fig. S5. Original images showing how one delivery site in each image has been addressed.
    • fig. S6. Image of an array with biologically relevant pixel spacing (200-μm spacing between pixels).
    • fig. S7. Simulated 5-s delivery pulses using simple circuit model.
    • Reference (25)

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