Improved longevity and in vivo performance of neurotransmitter detection using 30 μm cone-shaped carbon fiber microelectrode

Abstract

Fast Scan Cyclic Voltammetry (FSCV) is a widely used electrochemical technique to detect rapid extracellular dopamine transients in vivo. It employs carbon fiber microelectrodes (CFMEs), but conventional 7 mu m diameter CFMEs often suffer from limited mechanical durability and reduced lifespan, hindering their use in chronic monitoring. To improve mechanical robustness and long-term functionality, we fabricated 30 mu m diameter CFMEs and modified their geometry via electrochemical etching to form cone-shaped tips. We compared the in vitro and in vivo performance of 7 mu m, 30 mu m bare, and 30 mu m cone-shaped CFMEs using FSCV. Electrode longevity was assessed, and biocompatibility was evaluated via immunofluorescence analysis of brain tissue. In vitro, the 30 mu m bare CFMEs showed 2.7-fold higher sensitivity (33.3 +/- 5.9 pA/mu m2, n = 5) compared to 7 mu m CFMEs (12.2 +/- 4.9 pA/mu m2, n = 5). However, in vivo dopamine detection was significantly reduced in 30 mu m bare CFMEs (12.9 +/- 8.1 nA, n = 5) relative to 7 mu m CFMEs (24.6 +/- 8.5 nA, n = 5), likely due to tissue damage. Cone-shaped modification of 30 mu m CFMEs resulted in a 3.7-fold improvement in vivo dopamine signals (47.5 +/- 19.8 nA, n = 5) and significantly lower glial activation based on Iba1 and GFAP markers. Furthermore, erosion tests revealed a 4.7-fold increase in lifespan compared to 7 mu m CFMEs. These results suggest that while increasing CFME diameter improves sensitivity, it also increases tissue damage in vivo. The cone-shaped geometry effectively mitigates insertion-induced damage, enhancing in vivo performance and biocompatibility. This design offers a promising approach for long-term neurotransmitter monitoring and potential integration into closed-loop neuromodulation systems.