ESE Thesis Defense: “A Microwell-Based Impedance Sensor in Microneedle Shape for Cytokine Detection”

Monitoring cytokine profiles plays a crucial role in predictive and early disease diagnosis, as well as in research in many biological fields, thus multiple approaches have been investigated. Despite the promise of these techniques, many still require specialized instrumentation or have not been shown in real-time applications, impeding their clinical adoption as point-of-care systems. Impedance-based protein detection sensors for point-of-care diagnostics require quantitative specificity as well as rapid or real-time operation. Furthermore, microfabrication of these sensors can lead to form factors suitable for in vivo operation.

Herein, we present microfabricated needle-shaped microwell impedance sensors for rapid sample-to-answer, label-free detection of cytokines. The sensor utilizes a micro-well array configuration at the microneedle tip to enable label-free detection while simultaneously maintaining the capability of high sensitivity detection, despite the high salt concentration of complex biological fluids. The microneedle form factor allows the sensors to be utilized in transcutaneous or transvascular sensing applications. In vitro experimental characterization confirmed sensor specificity and sensitivity to multiple proteins of interest. Mechanical characterization demonstrated sufficient microneedle robustness for transcutaneous insertion, as well as preserved sensor function post-insertion. We further utilized these sensors to carry out real-time in vivo quantification of human interleukin 8 (hIL8) concentration levels in the blood of transgenic mice that endogenously express hIL8. To assess sensor functionality, hIL8 concentration levels in serum samples from the same mice were quantified by ELISA. Excellent agreement between real-time in vivo sensor readouts in blood and subsequent ELISA serum assays was observed over multiple transgenic mice expressing hIL8 concentrations from 62 pg/mL to 539 ng/mL. Further, to reduce large mechanical mismatch between fused silica microneedle and surrounding soft tissue thus explore potential chronic applications, materials with lower Young’s modulus (e.g., Parylene materials) have been employed in the microneedle fabrication. Moreover, the relative sizes of microwell array and needle footprint offer the potential for multiple bioassay sensors on a single microneedle by functionalizing the surface of each sensor with distinct antibodies, forming a full sensor platform. Such multiplexed sensors could allow the real-time assessment of more complex diseases or conditions in vivo.

Advisor: Dr. Mark G. Allen, Alfred Fitler Moore Professor, Department of Electrical and Systems Engineering

Dissertation Committee:
Chair:
Dr. David Issadore, Associate Professor, Department of Bioengineering, University of Pennsylvania
Members:
Dr. A.T. Charlie Johnson, Rebecca W. Bushnell Professor, Department of Electrical and Systems Engineering, University of Pennsylvania
Dr. Flavia Vitale, Assistant Professor, Department of Bioengineering, University of Pennsylvania