Fig 1.
Schematics of the light-addressable potentiometric sensor (LAPS) and the proposed miniature hybrid device.
a. An illustration of the LAPS and its light-addressing working principle show the photocurrent can ‘sample’ the extracellular electrophysiological potentials. b. The mapping of neuronal dynamics via the proposed label-free hybrid device is realized via raster-scanning of the light source. Thus, the information of neuronal dynamics at different measurement spots can be deciphered by the localized photocurrent induced by the focused light beam.
Fig 2.
Characterization of the LAPS chips.
a. Optical microscope image of the diced LAPS chips (scale bar = 200 μm) b. Capacitance versus voltage curve of the miniaturized LAPS chip indicating its inversion, depletion and accumulation region. c-d. Normalized amplitude (I, c) and phase (θ, d) of photocurrent versus bias voltage (V) in response to solutions with different pH. e-f. The pH sensitivity characterized from the I-V (e) and θ-V (f) curves.
Fig 3.
Fiber fabrication and characterization.
a. An illustration of the first step of the thermal drawing process. b. A photograph of the PC/PMMA preform. c-d. Optical microscope images of the thermally drawn PC/PMMA fiber without (c) and with (d) light confined within the PC core. Scale bar = 200 μm. e. An illustration of the second step of the thermal drawing process. f-g. A photograph of the preform (scale bar = 1 cm, f) and an optical microscope image of the thermally drawn fiber (g) with 108-waveguide bundle. Scale bar = 100 μm. h. An illustration of the fabrication process for the multifunctional fiber with an optical-waveguide bundle core and bismuth-tin alloy (BiSn) electrodes. i. An optical microscope image of the thermally drawn fiber illustrated in (h). Scale bar = 100 μm. j. An optical loss spectrum of a single PC/PMMA optical fiber. k. An optical loss spectrum of the fiber with a bundle of 108 PC/PMMA waveguides. l. An optical micrograph of light confinement within a single waveguide. Light intensity distribution profiles are shown in upper and left panels. Black cross indicates the illuminated waveguide center. Scale bar = 100 μm.
Fig 4.
Characterization of the fiber-coupled LAPS device.
a. A photograph of a fiber-coupled LAPS endoscope and its connections. b. Normalized photocurrent amplitude (I) vs. voltage (V) recorded by the endoscope in solutions with pH 6, 7, 8, and 9 as indicated by the black arrow. c. The pH sensitivity of the endoscope calculated from the inflection point of the I-V curves in (b). d. Optical micrographs of a multifunctional fiber (i) with light addressing different single pixels indicated by the yellow arrows (ii-iv). Scale bar = 500 μm. e. An optical micrograph of a multifunctional fiber with light addressing two different locations as indicated by yellow and red arrows. Scale bar = 250 μm. f-g. Measurements of localized photocurrent responses of the device with light illuminating different spots. Scale bar = 100 μm.
Fig 5.
Evaluation of the fiber-coupled LAPS device in vivo for electrophysiological recordings.
a. The schematic illustrating experiments in vivo. b. Representative traces of photocurrent amplitude recorded in the mouse hippocampus. c. Power spectrum of the local field potentials recorded in the hippocampus of an anesthetized mouse. The green arrow points to the delta frequency band.