Interfacing neurons with carbon nanotubes: electrical signal transfer and synaptic stimulation in cultured brain circuits

Abstract

The unique properties of single-wall carbon nanotubes (SWNTs) and the application of nanotechnology to the nervous system may have a tremendous impact in the future developments of microsystems for neural prosthetics as well as immediate benefits for basic research. Despite increasing interest in neuroscience nanotechnologies, little is known about the electrical interactions between nanomaterials and neurons. We developed an integrated SWNT-neuron system to test whether electrical stimulation delivered via SWNT can induce neuronal signaling. To that aim, hippocampal cells were grown on pure SWNT substrates and patch clamped. We compared neuronal responses to voltage steps delivered either via conductive SWNT substrates or via the patch pipette. Our experimental results, supported by mathematical models to describe the electrical interactions occurring in SWNT-neuron hybrid systems, clearly indicate that SWNTs can directly stimulate brain circuit activity.

Figure 1.

Scanning electron microscopy images of cultured hippocampal neurons on SWNTs. A, High-magnification micrograph showing SWNT details. B–D, Subsequent micrographs at higher magnifications of neurons grown on SWNTs (10 d). Same sample as in A is shown. Note the healthy morphology of neurons and the outgrowth of neurites attaching to the SWNT surface. E, F, Details of the framed area in D. At higher magnifications, the intimate contacts between bundles of SWNT and neuronal membrane are clearly shown. Scale bar (in E): A, 1 μm; B, 200 μm; C, 25 μm; D, 10 μm; E, 2 μm; F, 450 nm.

Figure 2.

Electrical interactions between SWNTs and neurons. A, Spontaneous activity recorded from a 12 d cultured neuron, under current-clamp (top trace) or voltage-clamp (bottom trace) configurations. B, Sketch of the recording chamber. Tracings, Current steps elicited by SWNT stimulation recorded from a patch-clamped neuron (left) or in control-glass preparation (middle) or in SWNTs before sealing to a cell (right). C, Top, Current responses to 400-ms-long SWNT stimuli in a voltage-clamped neuron, summarized in the plot (0.2 V bins; n = 5). Bottom, Current responses in a voltage-clamped neuron elicited via the patch pipette by a step protocol, summarized in the plot (20 mV bins; n = 5). D, Postsynaptic events evoked via SWNT stimulation (*) and recorded under voltage-clamp (bottom) or current-clamp (top) configurations. E, Spontaneous patterned activity and SWNT stimulation. Note that similar waveforms could be evoked via SWNT stimuli (*). Bottom, Single evoked and spontaneous events, as indicated by bars.

Figure 3.

Modeling electrical stimulation delivered via the SWNT layer. A, B, Sketch of the bath (A) or of the whole-cell pipette configurations (B). The DC equivalent circuit of A is represented in C. For B, the hypothesis on the resistive–capacitive nature of the SWNT–cell coupling, as well as the quality of the whole-cell configuration, must become explicit. These are ideal whole-cell patch clamp with (E) or without (D) a resistive electrical coupling between the cytoplasm and SWNT. Finally, F equivalently captures both of the previous situations (D–F), under the hypothesis of a nonideal whole-cell configuration. The value of R_c in one case has the same meaning as in C but in the other, has the same meaning as in E.

Figure 4.

Simulated stimulations via the SWNT layer. Intracellular currents elicited by SWNT stimulation simulated in a model neuron in the presence (A) or absence (B) of SWNT and before sealing to a cell (C), as in Figure 2. The emission of single unclamped APs simulated in the models through holding voltage steps (D) or by SWNT-delivered stimulation (E), when incorporating the details of SEVC.