A Novel Diamond Microprobe for Neuro-Chemical and -Electrical Recording in Neural Prosthesis

This paper describes the design, microfabrication, and testing of a novel polycrystalline-diamond (poly-C)-based microprobe for possible applications in neural prosthesis. The probe utilizes undoped poly-C with a resistivity on the order of 10
⁵
Omega middot cm as a supporting material, which has a Young's modulus in the range of 400-1000 GPa and is biocompatible. Boron-doped poly-C with a resistivity on the order of 10
^-3
Omega middot cm is used as an electrode material, which provides a chemically stable surface for both chemical and electrical detections in neural studies. The probe has eight poly-C electrode sites with diameters ranging from 2 to 150 mum; the electrode capacitance is approximately 87 muF/cm
²
. The measured water potential window of the poly-C electrode spans across negative and positive electrode potentials and typically has a total value of 2.2 V in 1 M KCl. The smallest detectable concentration of norepinephrine (a neurotransmitter) was on the order of 10 nM. The poly-C probe has also been successfully implanted in the auditory cortex area of a guinea pig brain for in vivo neural studies. The recorded signal amplitude was 30-40 muV and had a duration of 1 ms.