  Advances in chip-scale photonic-electronic integration are enabling a new
generation of foundry-manufacturable implantable silicon neural probes
incorporating nanophotonic waveguides and microelectrodes for optogenetic
stimulation and electrophysiological recording in neuroscience research.
Further extending neural probe functionalities with integrated microfluidics is
a direct approach to achieve neurochemical injection and sampling capabilities.
In this work, we use two-photon polymerization 3D printing to integrate
microfluidic channels onto photonic neural probes, which include silicon
nitride nanophotonic waveguides and grating emitters. The customizability of 3D
printing enables a unique geometry of microfluidics that conforms to the shape
of each neural probe, enabling integration of microfluidics with a variety of
existing neural probes while avoiding the complexities of monolithic
microfluidics integration. We demonstrate the photonic and fluidic
functionalities of the neural probes via fluorescein injection in agarose gel
and photoloysis of caged fluorescein in solution and in flxed brain tissue.
