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

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.