Micro-electrodes for in situ temperature and bio-impedance measurement

Abstract With fast recovery time and effective in situ tumor tissue killing ability, thermal ablation has become a popular treatment for tumors compared with chemotherapy and radiation. The thermal dose measurement of current technology is usually accompanied by monitoring a large area impedance across two ablation catheters and the localized impedance measurement is difficult to achieve. In this work, thermal‐resistive sensor and impedance sensor are fabricated on the curved surface of a capillary tube with 1 mm outer diameter. The device is applied for real‐time in situ tissue impedance monitoring during thermal ablation. The calibrated thermal‐resistive sensors have an average temperature coefficient of resistance (TCR) of 0.00161 ± 5.9% °C‐1 with an accuracy of ±0.7 °C. By adding electro‐polymerized PEDOT:PSS (poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate)) on the 300 µm diameter gold electrodes, the interface impedance reduces two orders from 408 to 3.7 kΩ at 100 Hz. The Randles equivalent circuit model fittings show a two‐order improvement in the electrode capacitance from 7.29 to 753 nF. In the ex vivo porcine liver laser ablation test, the temperature of the porcine liver tissue can reach 70°C and the impedance would drop by 50% in less than 5 minutes. The integration of laser ablation fiber with the impedance and temperature sensors can further expand the laser ablation technique to smaller scale and for precise therapeutics.