Abstract: Described herein are variations of a sensor configured to generate a signal that is indicative of a concentration of an analyte in a fluid. The sensor may include a working electrode comprising an electrode material, a biorecognition layer disposed at least partially on the electrode material and comprising a biorecognition element that selectively and reversibly binds to an analyte, and an at least partially desiccated hydrogel disposed on the biorecognition layer. In some variations, the biorecognition element may be functionalized with a redox-active molecule and is configured to change conformation upon binding the analyte to move the redox-active molecule, closer to, or further from, the electrode material. In some variations, the biorecognition element may be an aptamer.

Abstract: Described herein are variations of a cortisol monitoring system, including a cortisol monitoring device. For example, a cortisol monitoring device may include a skin-penetrating microneedle array for use in measuring cortisol, such as in a continuous manner. The microneedle array may include, for example, at least one microneedle comprising a working electrode comprising a cortisol-sensing aptamer that selectively and reversibly binds to cortisol. The microneedle array may include, for example, at least one microneedle including a tapered distal portion having an insulated distal apex, and an electrode on a surface of the tapered distal portion located proximal to the insulated distal apex. At least some of the microneedles may be electrically isolated such that one or more electrodes is individually addressable.