Figure 1.
CNT fibril dielectrophoresis “pulling” stage assembled for this study.
(A) A motorized linear stage moves only in the vertical direction, pulling the tungsten wire out of the solution. (B) A electrochemically sharpened tungsten tip functioned as a source electrode. (C) A submerged metal ring functioned as a counter electrode. (D) CNT dispersed solution. (E) High-frequency AC power source.
Figure 2.
(A) A motorized linear stage moving only in the vertical direction. (B) A CNT probe. (C) Water droplet. (D) Gold plated surface for grounding. (E) Variable DC voltage source.
Figure 3.
(A) Low magnification view of a CNT probe. Tungsten wire extends from lower left to the white arrow; CNT probe extends from the arrow for 1.5 mm to upper right. (B) Tip of a CNT probe after dielectrophoresis. The tip tapers down to a single CNT (white arrow). (C) CNTs in the probe show a clearly self-entangled morphology. (D) A CNT probe tip after coating with 300 nm Parylene-C, which homogeneously covers the entire probe. (E) An exposed CNT probe tip after FIB cutting. Two FIB cutting planes are perpendicular to the picture, crossing at the end of the probe. (F) An angled view (at 40° with respect to the electron beam in the SEM) of exposed CNT probe tip shows the two cut planes. The FIB cutting did not damage nearby insulation coating, which is clearly visible (white arrow). Scale bars in (B)- (F): 1 µm.
Figure 4.
Impedance characterization of CNT probes.
(A) Cyclic Voltammetry (CV) shows the CNT probes (with the insulation and FIB cut) have significantly larger charge transfer (blue line), compared to the sharp intracellular-recording glass pipette (gray line). (B) Electrochemical impedance spectroscopy (EIS) shows significantly lower impedance of the CNT probe (blue line) compared to the glass pipette (gray line) over the frequency range of 1 to 100 kHz. Successful insulation-coating plus FIB-cutting reduces contact area between the CNT probe and solution by a few orders of magnitude, which explains the difference between the curves measured before coating (red line) and after FIB cutting (blue line).
Figure 5.
In vitro brain slice intracellular recording from mouse, cortical neurons.
(A) Light-evoked inhibitory post synaptic potential (IPSP) recorded with a CNT probe from a neuron in cortical brain slice prepared from a VGAT-CHR2 mouse. A brief light pulse was applied at the time marked by the arrow (Vm = −64 mV). (B) Expanded membrane potential records for CHR2 evoked IPSPs collected from four different cortical neurons. (C) Electrically-evoked excitatory postsynaptic potential (EPSP) from a cortical neuron in a mouse cortical brain slice (Vm = −54 mV). (D) Expanded membrane potential records of electrically-evoked EPSPs collected from four different cortical neurons.
Figure 6.
In vivo extracellular recordings from mouse brain somatosensory cortex.
Three different extracellular recordings show well-isolated single unit activity.