Microneedle Enabled Electrochemical Aptamer-Based Sensing: Real Time Measurements Using Stainless Steel Microneedles

Abstract

Electrochemical aptamer-based (EAB) sensors are among the only generalizable sensing platforms that resist fouling enough to function directly in bodily fluids and in situ in the living body. Already, these sensors have enabled the real-time measurement of a range of small molecule targets in vivo, including pharmaceuticals and drugs of abuse. EAB sensors consist of an electrode-attached, redox reporter-labeled aptamer that binds to its target species. Target binding causes a shift in electron-transfer rate between the redox reporter and electrode surface, easily detected by a range of electrochemical techniques. Here, we explore the application of EAB sensors to minimally-invasive molecular monitoring. Specifically, we adapt the platform to a microneedle device format. Microneedles can provide direct access to the skin’s interstitial space – a bodily compartment that holds valuable information ranging from drug distribution and immune status. And because microneedles can penetrate into the top layers of the skin with minimal nerve endings, they can avoid eliciting notable pain responses.In this work, we demonstrate the substantial miniaturization of the sensing platform into electrodes thinner than a human hair, and then integrate them with ultra-fine, hollow microneedles. To ensure needle sterilizability and sharpness while avoiding complex fabrication, we utilize commercial off the shelf stainless steel microneedles. Using an EAB sensor responding to the high-toxicity small molecule drug, vancomycin, as a model system, we achieve quantitative measurements directly in body temperature, undiluted whole blood. Building on this milestone, we explore the application of the sensors when inserted into porcine skin. In porcine skin (a common proxy for human skin), we observe facile microneedle penetration and stable electrochemical signaling. Because of the individual addressability of the sensing electrodes and the generalizability of the aptamer platform, this technology is capable of multiplexed, simultaneous detection of many different molecular targets. Thus, microneedle-enabled aptamer-based sensors offer a promising route forward for non-invasive physiological monitoring – applicable to therapeutic drug monitoring, pain-free biomarker detection, and disease management.