"Tone-Arm" Neuromodulation MEMS Microcoil for In Vivo Imaging

Implantable neural interfaces have revolutionized neuromodulation by enabling bidirectional communication between neural circuits and external devices. Yet, existing modalities face important challenges in precision, high invasiveness, and compatibility with advanced in vivo imaging systems. We report a MEMS-based "tone-arm" micro-coil design optimized for vertical cortical insertion, featuring an 800-µm cantilever with a small cross-section that reconciles mechanical robustness with two-photon microscopy compatible miniaturization. Numerical modeling spanning electromagnetic field gradients, thermodynamic safety margins, and buckling resistance guided our MEMS device design process. Our toxic-etchants-free 3-stage and 4-mask fabrication process yielded micro-coil devices compatible with in vivo two-photon imaging. Our vertically integrated probe design overcomes longstanding optical obstruction challenges, preserving >95% imaging field visibility during in vivo studies. This platform enables simultaneous micromagnetic neuromodulation and subcellular-resolution calcium imaging, opening unprecedented opportunities to dissect neural circuit dynamics during targeted intervention. Thermodynamic modelling showed the record low probe resistance (2 Ω) is safe for implantation and limits tissue heating to < 0.2°C. The low-invasive cross-section (70 × 86 µm²), and mechanical robust brain insertions were critical to achieving robust neuromodulation, including neuro-inhibition-a capability long sought for the potential treatment of hyperactivity-driven neurological disorders.