Immersion Lithographic Patterning of Electrospun Nanofibers for Carbon Nanofibrous Microelectrode Arrays

Immersion photolithography of electrospun SU-8 nanofibers followed by carbonization has been demonstrated for 3-D carbon nanofibrous microelectrodes. The process and resultant structures offer unique advantages: 1) precise patterning of nanofibrous microstructures via refractive index matching immersion photolithography; 2) good cell/neuron adhesion characteristic of the resultant scaffold attributed to nanomorphology in 100's nanometer scale; 3) high electrical conductivity of the carbonous microelectrodes appropriate for neural stimulation and signal detection; and 4) biocompatibility of the carbon nanofibers. Immiscible refractive index matching liquid, such as oil (n
_oil
= 1.47), has been applied to the nonhomogeneous nanofiber stack consisting of SU-8 nanofibers (nS
_U-8
= 1.67) and air (n
_air
= 1) before ultraviolet light exposure, which greatly suppresses optical diffraction and scattering effects, resulting in high aspect ratio 3-D nanofibrous microstructures and enhanced patterning resolution. The aspect ratio of the fabricated 3D structures is increased from 0.26 to 0.89 and the contrast ratio from 0.56 to 0.96, compared with ones from the nonimmersion process. Ray tracing simulation taking into account diffraction effects in nanofibrous media has been discussed. Microelectrode arrays consisting of integrated nanofibers and thin-film carbon structures are implemented for in vitro neuron culture experiments. Experimental results of structure's surface roughness, electrical conductivity, and cell viability on them are detailed.