Micro Electrical Impedance Spectroscopy (μEIS) Fabricated on the Curved Surface of a Fine Needle for Biotissue Discrimination

Abstract

This work presents a novel micro electrical impedance spectroscopy (μEIS) technique that can measure and discriminate the electrical signal responses of biotissues in real time. An EoN (EIS‐on‐a‐needle), EIS on the surface of a fine needle (400 μm in diameter), was fabricated using a newly developed flexible photomask film. The base material of the photomask is parylene‐C, which allows uniform contact on the curved surface of the needle; thus, the designed electrode patterns of the photomask can be transferred onto the needle surface with a high resolution (2.95 % or less in dimensional error). To validate the developed EoN as an electrical sensor, ex vivo experiments with various biotissues—butchered pork (skin, fat, and muscle) and human breast tissues (normal and cancerous)—were conducted by measuring real‐time electrical impedance during a frequency sweep. The conductivities (relative permittivity) of the pork tissues were evaluated by electrical equivalent circuit analysis: 56.6 mS/m (37,800), 68.0 mS/m (74,755), and 74.9 mS/m (26,145) for the skin, fat, and muscle, respectively. Moreover, the normal and cancerous tissues were well distinguished by electrical resistance at 4.04 kHz for various cancer grades (Elston grades 1, 2, and 3). Analysis of the electrical impedance suggests that the EoN can be utilized to diagnose the physiological states of biotissues in clinical use.

A Review of Recent Advancements in Sensor‐Integrated Medical Tools

“…Therefore, various researchers have tried to mitigate these limitations by fabricating electrodes directly on the needle surface for impedance measurement. For example, micro‐scaled electrodes could be successfully constructed on the needle surface (diameter = 0.4 mm) using traditional microfabrication techniques such as lithography and metal deposition [ 27 , 28 , 29 ] (Figure 2a(iii) ). For the pattern formation on the curved needle surface, specialized zig and pattern masks based on the bulk micromachining process were adopted.…”

Electronic sensing and ablation needles for medical diagnosis and treatment

“…Giseok Kang et al further improved the IDE by applying a newly developed exible photomask: Parylene-C lm, in the fabrication process [15]. Two types of EoN were designed and fabricated for the comparison experiments, and they were classi ed into open type (electrodes of open type are exposed to the air) and passivation type (Parylene-C passivates electrodes of passivation type).…”

“…To increase the accuracy of tissue discrimination, EIS has been studied by many researchers to create a cancer diagnosis system. This is due to EIS having the potential to differentiate healthy tissue from unhealthy tissue by observing the variation of multiple references of impedance data (real/imaginary part of magnitude and phase angle) at different frequencies [8,9,[15][16][17][18]. On the other hand, radio frequency (RF) in medical engineering refers to the frequency range of electromagnetic waves that lie about 900Hz to 2500MHz.…”

Fabrication of a Gold Dual‐microelectrode Patterned on a Silicone Substrate Probe for the Discrimination of Different Tissues

“…Kang et al developed an interdigitated electrode on a curved needle using a parylene‐C photolithography mask. They describe the use of a sensorised needle to differentiate between phantom and different pork tissues of varying conductivity [26].…”