Microwell-array on a flexible needle: A transcutaneous insertable impedance sensor for label-free cytokine detection

Measurement of various specific proteins in body fluids can be a key component of continuous health monitoring. The gold-standard technique for protein quantification is ELISA, which typically relies on labeling and optical fluorescence. Impedance sensors provide a promising alternative due to ease of miniaturization, rapid readout and label-free operation; yet lag their fluorescent counterparts in terms of sensitivity. We present a flexible micromachined needle-shaped impedance sensor for label-free in-situ detection of cytokines and other biomarkers. The sensor utilizes a micro-well array configuration at the needle tip to enable label-free detection while simultaneously maintaining the capability of high sensitivity detection, despite the high salt concentration of complex biological fluids. Real-time label-free detection is achieved in an in vitro skin phantom by monitoring the impedance change of the sensor electrodes as specific binding of target proteins to antibodies on the sensor surface occurs.