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.

Bioelectrical Impedance Spectroscopy for Monitoring Mammalian Cells and Tissues under Different Frequency Domains: A Review

“…While acknowledged within, this review is not concerned with whole body composition analysis to which the reader is directed to excellent recent reviews on this topic. 12,13 Of emerging significance is bioimpedance monitoring with simultaneous therapeutic intervention, 10 perioperative and postoperative monitoring, 14,15 and surgical guidance, 16 which is the focus of the present review.…”

“…Bioelectrical impedance analysis (BIA), bioelectrical impedance spectroscopy (BIS), and bioimpedance tomography (BIT) have firmly established themselves as appropriate modalities for measurement and monitoring to accommodate diagnostics and prognostics in clinical care. With established applications in body composition analysis, where the goal is to aid diagnosis, monitor disease progression, support therapeutic interventions, and better elucidate disease mechanisms, bioimpedance is now being fervently applied at the cellular, − tissue, − and organ levels , with similar goals in mind. While acknowledged within, this review is not concerned with whole body composition analysis to which the reader is directed to excellent recent reviews on this topic. , Of emerging significance is bioimpedance monitoring with simultaneous therapeutic intervention, perioperative and postoperative monitoring, , and surgical guidance, which is the focus of the present review.…”

Microfabricated Polymer-Metal Biosensors For Multifarious Data Collection From Electrogenic Cellular Models

“…. The values and tted signature imply a more capacitive dominance of the circuit at 1 kHz, which we experimentally have hypothesized is due to the usage of silver epoxy with enhanced surface porosity in the nanoscale to de ne the packaging traces 34 . It is important to state as well that while various circuit elements will change the impedance and phase signatures of microelectrodes, it has not been fully established if these differential values across device fabrication approaches are large enough to impact the overall performance of the microelectrodes, although we have begun to explore these questions 30 .…”

“…In general, lower frequencies are susceptible to high levels of environmental noise, which can produce unreliable results 26 . Since the evaluation of temperature utilizing an impedimetric sensor would be largely in uenced by the energetic activation of dissolved ionic species in media, it was determined that higher frequencies were more likely to present a reproducible and consistent temperature change measurement 34 . As the temperatures being measured were in the physiologically relevant range (22°C to 42°C) and were not high enough for large evaporation to occur, a decrease in impedance was expected due to increased ionic species motility 34 .…”

“…Since the evaluation of temperature utilizing an impedimetric sensor would be largely in uenced by the energetic activation of dissolved ionic species in media, it was determined that higher frequencies were more likely to present a reproducible and consistent temperature change measurement 34 . As the temperatures being measured were in the physiologically relevant range (22°C to 42°C) and were not high enough for large evaporation to occur, a decrease in impedance was expected due to increased ionic species motility 34 . If temperatures of interest were much higher, then an increase in impedance would be expected with resultant relative increased concentrations of ionic species, from reduced solution volumes.…”