In-vivo biotissue discrimination using electrochemical impedance spectroscopy on a hypodermic needle with fine interdigitated electrodes

This paper reports the first demonstration of electrochemical impedance spectroscopy-on-a needle (EoN) applied to in-vivo biotissue discrimination. A flexible photomask and photoresist spray coating were employed in the photolithography process to fabricate fine interdigitated electrodes (IDEs) patterns (overall length of 300 μm) at the tip of the round surface of the needle. Prior to main in-vivo experiment, the discrimination capability of the EoN was evaluated at various concentration levels of PBS solution with known electrical properties. Electrical parasitic influence was also investigated as the penetration depth of the IDEs increases. Finally, an in-vivo experiment was conducted to discriminate different kinds of biotissues; the EoN successfully discriminated the fat and muscle tissues of a rat.