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Introduction In the future, asymmetric conflicts are expected to make robust, on-site medical support more challenging, leading to delays in critical medical interventions and poorer outcomes. Currently, patients in forward operating environments are assessed using single-use blood analysers that require trained medical personnel, costly single-use cartridges, and invasive blood draws to operate. Next generation technologies need to continuously monitor health status, provide critical alerts to medical personnel, and help prioritize treatment and evacuation. Additionally, these closed loop sensors can be programmed to deliver certain biochemical interventions, allowing for remote patient stabilization and extending the time available for treatment or evacuation of far-forward casualties ( figure 1). To address these needs, we are developing electrochemical-based microneedle patches to continuously monitor medically relevant biomarkers in the dermal interstitial fluid (dISF) in real time. Here we describe prototype devices for cortisol and four molecules from the Chem-8 panel.Abstract P09 Figure 1Concept of operation for a wearable sensor measuring biomarkers in the dermal interstitial fluid, providing real time status update to medical personnel for remote assessment and triage decision-making. Image generated using OpenArt.aiMethods and Results A wearable sensor platform was designed using microneedles and an electrochemical sensing platform for continuous sensing. The microneedles were decorated with different sensing chemistries designed to be inserted into the dermis layer of the skin with the purpose of continuous monitoring different analytes related to patient status and stress levels. This platform will provide real-time data to assess how a patient is responding to treatment, information that is critical for triage decision-making and to plan for care through the continuum of care ( figure 1).For detection of the stress hormone cortisol, we developed a structure-switching DNA aptamer1 to act as a bio-recognition element (BRE) for the electrochemical sensor. When tagged with a redox-reactive reporter (methylene blue) and immobilized onto gold-plated electrodes, it generates a rapid and reversible current change directly correlated to cortisol concentrations. Sensors were optimized to respond in the physiological range of cortisol in dISF and achieved a limit of detection of 10 nM. When transitioned to a prototype device (4 microneedle platform with 1 reference, 1 counter, and 2 sensor electrodes), the sensors demonstrate sensing in simulated dISF. Additionally, ex vivo porcine tissue testing was performed demonstrating the sensor can function over multiple hours.Next, we selected analytes commonly measured in the Chem-8 basic metabolic panel used to assess the body’s electrolyte balance, blood sugar status, and organ function. Commercially available stainless steel microneedle arrays were plated with gold, platinum (over gold), or carbon. Electrochemical sensors were fabricated using a selection of ion-selective membranes (ISEs) and enzymes. ISEs were produced for sodium (Na+) and potassium (K+) by electrodepositing conductive polymers (PEDOT:PSS) onto carbon-plated microneedles followed by a mixture of an ionophore, plasticizer, charge carrier, and membrane. Enzymatic sensors for glucose and lactate were produced by coating platinum-plated electrodes with either glucose oxidase (Gox) or lactate oxidase (Lox), respectively. All sensors produced linear responses within physiological concentration ranges found in dISF. ISE sensors showed linear responses in ex vivo porcine tissue over multiple hours. Some delamination of the carbon sensor tip was observed post-insertion into porcine skin and requires further optimization. Testing of the enzymatic sensors is ongoing. A prototype device is being developed that integrates all four sensors onto a PCB board that can be connected to a portable potentiostat for on-body monitoring.Conclusions We have developed two ion-selective sensors for Na + and K+; two enzymatic sensors for glucose and lactate; and one aptameric sensor for cortisol. All electrochemical sensors have been validated on microneedle arrays and are being integrated into prototype devices for future testing in human trials. Second generation devices will include mechanisms to deliver interventions for autonomous patient care.Disclaimer The views expressed are those of the authors and do not reflect the official guidance or position of the United States Government, the Department of Defense or the United States Air Force. Unless otherwise noted, imagery in this document are property of the U.S. Air Force. This item was cleared on August 5, 2025, Case Number: 2025–0708.References Wolfe M, Cramer A, Webb S, et al. Rational approach to optimizing conformation-switching aptamers for biosensing applications. ACS Sens. 2024 Feb 23;9(2):717–725