<p dir="ltr">Depression affects over 20 million adults in the US every year. It has been shown that depression is correlated with dysregulation of the hypothalamic-pituitary-adrenal axis, resulting in elevated cortisol levels which return to normal following successful treatment. Tracking cortisol as a physiological biomarker of depression could be used to complement traditional diagnosis and treatment monitoring. In this work, I aim to develop a minimally invasive method of measuring cortisol concentrations at the point of care.</p><p dir="ltr">The two main goals of this research are to implement a simple, painless sample collection method via hydrogel microneedles, and develop an electrochemical biosensor to measure and track cortisol concentrations at the point of care. Interstitial fluid is a rich source of biomarkers, including cortisol, found just beneath the surface of the skin. Hydrogel microneedles are used to painlessly sample interstitial fluid, but typically require sample processing to isolate the biomarker for measurement. Here, a rapid swelling methacrylated hyaluronic acid hydrogel microneedle platform is used to passively sample interstitial fluid from skin. Single-use gold leaf electrodes are functionalized with an aptamer to measure cortisol concentration directly from the hydrogel matrix without the need for sample processing.</p><p dir="ltr">Together, these platforms for interstitial fluid sampling and cortisol measurement will provide a minimally invasive, user friendly tool for monitoring depression throughout the course of treatment that can benefit the millions of people affected by depression.</p>