Polydimethylsiloxane (PDMS)-Based Flexible Optical Electrodes with Conductive Composite Hydrogels Integrated Probe for Optogenetics

Optical electrodes are important tools for optogenetic research. Flexible optical electrodes represent a refinement over traditional fiber-based electrodes because they contact with target cells gently by reducing mechanical mismatch, thereby enhancing their long-term, stable signal acquisition capability. Until now, little attention has been paid to flexible intracortical optical electrodes. Here, we reported a novel flexible penetrating optical electrode with a probe made of composite hydrogels. We used polydimethylsiloxane (PDMS), a kind of transparent material, to fabricate waveguide by capillary assembly method with two tungsten wires inside providing mechanic support. Then one tungsten wire was withdrawn out and the microchannel was filled with hydrogel composed of polyvinyl alcohol (PVA), multi-walled carbon nanotubes (MWCNT), poly(3,4-ethylenedioxythiophene) (PEDOT), and polystyrene sulfonate (PSS) as an electrical recording and stimulation probe. With PDMS as the waveguide and PVA/MWCNT/PEDOT/PSS hydrogel as the electroprobe, the optical electrode becomes a flexible package. The morphology observed by scanning electron microscopy showed that the PVA/MWCNT/PEDOT/PSS hydrogel had a loose surface structure, which would allow the effective adhesion to target neurons. A buckling test showed that our electrode maintained bending strength comparable to that of previously reported flexible penetrating electrodes. Finally, the electrical properties showed a lower impedance and higher charge capacity after PEDOT/PSS modification. The flexible penetrating optical electrode we developed may be used for long-term in vivo optogenetics studies.