A ten-minute, single step, label-free, sample-to-answer assay for qualitative detection of cytokines in serum at femtomolar levels.

Label-free electronic affinity based immuno-sensing is an attractive candidate as a platform technology for analyzing biomarkers due to the ease of miniaturization and minimal use of reagents. Electronic based sensing approaches, however, have lagged behind their optical counterparts in terms of detection limit, selectivity, and reliability. Also, the matrix dependent nature of electronic sensing modalities makes difficult the analysis of biomarkers in high salt concentration samples such as serum due to charge screening. We present a novel sensing platform, the micro-well sensor, that works by functionalizing nanoscale volume wells with antibodies and monitoring the impedance change inside the wells due binding of target protein. This detection modality is advantageous to many label-free electronic sensors in that signal power scales with increase in salt concentration, thus improving the sensitivity of the platform. We demonstrate rapid label-free qualitative detection of cytokines within ten minutes at femtoMolar concentrations and a dynamic range of 3 orders of magnitude in serum samples. We describe the design, fabrication, and characterization of the micro-well sensor in serum samples using inflammatory protein biomarkers.