Research ArticleNEUROSCIENCE

Transparent arrays of bilayer-nanomesh microelectrodes for simultaneous electrophysiology and two-photon imaging in the brain

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Science Advances  05 Sep 2018:
Vol. 4, no. 9, eaat0626
DOI: 10.1126/sciadv.aat0626
  • Fig. 1 Materials, fabrication strategies, and performance benchmarking of transparent, bilayer-nanomesh MEAs.

    (A) Photograph of a 32-channel Au/PEDOT:PSS nanomesh MEA wrapped on a paper rod. Scale bar, 1 mm. (B) Device schematic of the 32-channel Au/PEDOT:PSS nanomesh MEA in (A). (C) Left: Microscope image of a Au/PEDOT:PSS bilayer-nanomesh microelectrode (20 μm in diameter). Right: SEM image of a zoomed-in region of the microelectrode shown on the left. (D) Fabrication process of the bilayer-nanomesh MEAs. (E) Impedance of different bilayer-nanomesh microelectrodes versus electrode site area. Results from bilayer-nanomesh microelectrodes are benchmarked against the ones from major transparent MEAs from graphene, ITO, and nontransparent Michigan arrays. NM, nanomesh.

  • Fig. 2 Bench testing of 32-channel bilayer-nanomesh MEAs.

    (A) Impedance magnitude and phase spectra of the 31 working electrodes in a 32-channel Au/PEDOT:PSS bilayer-nanomesh MEA. (B) Electrode impedance histogram of the 32-channel Au/PEDOT:PSS nanomesh MEA in (A). Inset: Impedance colormap with respect to actual channel position. (C) Bench recording output of a 1000-Hz, 316 Vp-p sine wave input using the Au/PEDOT:PSS nanomesh MEA in (A). (D) Power spectra density of recorded sine wave output in (C). (E) SNR histogram from all electrodes with the bench recording in (C). Inset: SNR colormap with respect to actual channel position. (F) Histogram of charge injection limit of all electrodes from the 32-channel Au/PEDOT:PSS nanomesh MEA in (A). Inset: Charge injection limit color map with respect to actual channel position. (G) Average electrode impedance and array yield as a function of bending cycles with a bending radius of 4 mm. (H) Average electrode impedance as a function of weeks after soaking for devices immersed in PBS (pH 7.4) under 37°C. (I) Electrode impedance as a function of stimulating cycles with current pulses (0.35 mC/cm2). (J) Schematic of the experimental setup of the wireless recording with stimulation artifact rejection with the 32-channel Au/PEDOT:PSS nanomesh MEA. (K) Input neural signal contaminated with large stimulation artifacts. (L) Ground truth neural signal overlapped with artifact rejection output (left y axis) and wireless output (right y axis) for comparison. PSD, power spectra density; Tx, transmitter; Rx, receiver; LSB, least significant bit.

  • Fig. 3 Surgery procedure and in vivo histology studies of bilayer-nanomesh MEAs.

    (A) Schemes of the sequence of the experiments, the positions of the MEA and the cranial window on the mouse brain. (B) Installation of the headbar. (C) Implantation of the transparent MEA on the brain. (D) Enclosure of the transparent MEA with the cranial window. (E and F) IBA1 staining for evaluating possible microglia activation on the control cortex (E) and on the cortex implanted only with the transparent MEA (F).

  • Fig. 4 Simultaneous two-photon Ca++ imaging and electrophysiological recording from a bilayer-nanomesh MEA on the brain of an awake mouse.

    (A) Head-restrained awake mouse on a floating styrofoam ball, watching visual stimuli. (B) Wide-field epifluorescence of the visual cortex and the surrounding areas. The asterisk indicates the binocular area of the visual cortex. (C) Temporal autocorrelation from a two-photon imaging movie (1-s lag), indicating neurons expressing the Ca++ indicator GCaMP6s. (D) Simultaneous electrophysiology recording (spectrogram, top), arousal (pupil diameter, middle), and two-photon imaging (ΔF/F traces representing single-neuron Ca++ activity (bottom). (E) Magnification of the spectrogram and Ca++ traces during the onset of a spontaneously induced high arousal event. Each square contains the increase in magnitude of the 32-channel electrophysiology signal in a specific frequency band (from top to bottom: α, β, γ, high γ, ultrahigh γ, and multi-unit). The dashed line is a guide to the eyes to show when the average GCaMP expression is rising (the line corresponds to the 50% of the maximum ΔF/F). (F) Modulation of the power in the high-frequency band (average on all 32 channels) during the alternation of visual stimuli and gray screen. (G) Visual-evoked response in the time domain (lower frequency). The asterisk indicates the position of the binocular area of the visual cortex. LCD, liquid crystal display.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/9/eaat0626/DC1

    Fig. S1. Bilayer-nanomesh structure and transmittance study.

    Fig. S2. Bilayer-nanomesh microelectrode demonstration.

    Fig. S3. Impedance results from different bilayer-nanomesh MEAs.

    Fig. S4. Bench-top sine wave signal recording.

    Fig. S5. Light-induced artifact characterization.

    Fig. S6. Demonstration of artifact-free, ITO/PEDOT:PSS bilayer-nanomesh microelectrodes.

    Fig. S7. Artifact rejection and wireless recording system.

    Fig. S8. Artifact rejection using Au nanomesh microelectrode.

    Fig. S9. Histology studies.

    Fig. S10. In vivo transparency of MEA.

    Fig. S11. Optical imaging underneath microelectrode.

    Fig. S12. In vivo impedance measurement after implantation.

    Fig. S13. Optimization of nanosphere lithography.

    Movie S1. Wide-field epifluorescence of the Ca++ indicator GCaMP6s showing the activity in the superficial layers of the mouse visual cortex and the surrounding areas (30× faster than the real time).

    Movie S2. Video-rate two-photon Ca++ imaging from the neurons of the layer 2/3 of the mouse visual cortex expressing the Ca++ indicator GCaMP6s (30× faster than the real time).

    Movie S3. Correlation between the ΔF/F of Ca++ wide-field epifluorescence and the MEA recording (30× faster).

    Movie S4. The correlated response of arousal (left), the map of the modulation of the power of the MEA recording in different electrophysiology frequency bands (center), and the ΔF/F of the two-photon Ca++ imaging (right) (3× faster than the real time).

    Movie S5. Map of the modulation of the power of the MEA recording in the multi-unit band (300 Hz to 7 kHz) during the alternation of visual stimuli and isoluminous gray screen presentations (3× faster than the recording) in which evoked cortical activity (higher, color-coded in red) alternates with spontaneous cortical activity (lower, color-coded in green) based on the stimulus/nonstimulus presentation.

  • Supplementary Materials

    The PDF file includes:

    • Fig. S1. Bilayer-nanomesh structure and transmittance study.
    • Fig. S2. Bilayer-nanomesh microelectrode demonstration.
    • Fig. S3. Impedance results from different bilayer-nanomesh MEAs.
    • Fig. S4. Bench-top sine wave signal recording.
    • Fig. S5. Light-induced artifact characterization.
    • Fig. S6. Demonstration of artifact-free, ITO/PEDOT:PSS bilayer-nanomesh microelectrodes.
    • Fig. S7. Artifact rejection and wireless recording system.
    • Fig. S8. Artifact rejection using Au nanomesh microelectrode.
    • Fig. S9. Histology studies.
    • Fig. S10. In vivo transparency of MEA.
    • Fig. S11. Optical imaging underneath microelectrode.
    • Fig. S12. In vivo impedance measurement after implantation.
    • Fig. S13. Optimization of nanosphere lithography.
    • Legends for movies S1 to S5

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). Wide-field epifluorescence of the Ca++ indicator GCaMP6s showing the activity in the superficial layers of the mouse visual cortex and the surrounding areas (30× faster than the real time).
    • Movie S2 (.mp4 format). Video-rate two-photon Ca++ imaging from the neurons of the layer 2/3 of the mouse visual cortex expressing the Ca++ indicator GCaMP6s (30× faster than the real time).
    • Movie S3 (.avi format). Correlation between the ΔF/F of Ca++ wide-field epifluorescence and the MEA recording (30× faster).
    • Movie S4 (.mp4 format). The correlated response of arousal (left), the map of the modulation of the power of the MEA recording in different electrophysiology frequency bands (center), and the ΔF/F of the two-photon Ca++ imaging (right) (3× faster than the real time).
    • Movie S5 (.mp4 format). Map of the modulation of the power of the MEA recording in the multi-unit band (300 Hz to 7 kHz) during the alternation of visual stimuli and isoluminous gray screen presentations (3× faster than the recording) in which evoked cortical activity (higher, color-coded in red) alternates with spontaneous cortical activity (lower, color-coded in green) based on the stimulus/nonstimulus presentation.

    Files in this Data Supplement:

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