Improved Longevity and In Vivo Performance of Neurotransmitter Detection using 30 µm Cone-Shaped Carbon Fiber Microelectrode

Haeun Kwon¹Hyun-U Cho¹Jeongeun Sim¹Kyung-Jun Boo²Yumin Kang³Sangmun Hwang¹Youngjong Kwak¹Jaehyun Jang¹Se Jin Jeon⁴Chan Young Shin²Kevin Elliott Bennet⁵Yoonbae Oh⁵Hojin Shin⁵Kendall H Lee⁵Dong Pyo Jang^1*

• ¹Hanyang University, Seoul, Republic of Korea
• ²Konkuk University, Seoul, Seoul, Republic of Korea
• ³SOSO H&C Co., Seoul, Republic of Korea
• ⁴Hallym University, Chuncheon-si, Gangwon, Republic of Korea
• ⁵Mayo Clinic, Rochester, Minnesota, United States

Fast Scan Cyclic Voltammetry (FSCV) is widely used to detect rapid extracellular dopamine transients in vivo. It employs carbon fiber microelectrodes (CFMEs), but conventional 7 µm diameter CFMEs struggle with sustained measurements due to their fragility and limited lifespan in implantable applications. This study compared the sensitivity and in vivo performance of 30 µm and 7 µm CFMEs. The 30 µm bare CFMEs demonstrated 2.7-fold higher in vitro sensitivity (33.3 ± 5.9 pA/µm², n = 5) than the 7 µm CFMEs (12.2 ± 4.9 pA/µm², n = 5). However, in vivo measurements revealed reduced dopamine detection (12.9 ± 8.1 nA, n = 5) compared to 7 µm CFMEs (24.6 ± 8.5 nA, n = 5), likely due to tissue damage from thicker and blunter insertion. To mitigate tissue damage, we electrochemically etched the tips of the 30 µm CFMEs into a cone. The 30 µm cone-shaped CFMEs demonstrated a 3.7fold improvement in vivo dopamine response compared to 30 µm bare CFMEs, with no significant difference in vitro sensitivity. Immunofluorescence analysis confirmed reduced tissue damage with the 30 µm cone-shaped CFMEs. Furthermore, erosion tests indicated that the 30 µm cone-shaped CFMEs had 4.7 times longer lifespan than the 7 µm CFMEs. In conclusion, the 30 µm coneshaped CFMEs enhanced sensitivity, biocompatibility, and longevity, making them strong candidates for chronic neurotransmitter monitoring and closed-loop DBS applications.