Drug overdose is now the leading cause of death for Americans under 50 years old, with fentanyl claiming more lives than any other drug. Alarmingly, the problem is increasing, with fentanyl overdoses claiming nearly twice as many lives in 2016 compared to 2015. In addition to users, first responders are at risk for exposure to fentanyl as they perform their duties. Fentanyl is extremely dangerous because it is odorless and lethal in small quantities. A low-cost, wearable detector for fentanyl could reduce time from exposure to treatment, saving the lives of first responders and other vulnerable groups. Chemical sensors are ideal for a low-cost, wearable detector. However, fentanyl is typically found in particles and most chemical sensors are designed to detect gas molecules. Fentanyl is generally found as a salt and is nonvolatile. In Phase I, Vaporsens demonstrated a novel sensor that converts the salt at program-relevant levels to a detectable form of fentanyl. Importantly, the same sensors did not respond to common cutting agents, including lactose and mannitol. In Phase II, the sensors will be refined for improved performance. Wearable prototype systems will be developed that are small in size and consume little power. The prototypes will be tested in a laboratory setting for sensitivity to fentanyl and through field trials with first responders to determine the likelihood of false alarms in a real-world setting. The proposed sensors could play a vital role in protecting first responders from becoming victims of the opioid epidemic.