A patch smaller than a penny could one day save the lives of people experiencing a fentanyl overdose – even when no one else is there to help.
Researchers in Virginia Tech’s Department of Biological Systems Engineering have developed a wearable microneedle patch that can detect fentanyl in the body and automatically release naloxone, a medication that can reverse an opioid overdose. The technology could change how opioid overdoses are treated by making lifesaving intervention possible without relying on a bystander.
The patch, called the iNal patch, was developed by a research team led by Wujin Sun , assistant professor of biological systems engineering, which is in both the College of Agriculture and Life Sciences and the College of Engineering . The team's findings were recently published in Advanced Science .
“In general situations when there’s an overdose, we need to have someone there to save you,” Sun said. “In this case, we don’t need a bystander because we’re protected all the time.”
The patch uses an array of 121 microscopic needles to reach the fluid just beneath the skin. When pressed into place, the needles penetrate only far enough to access that fluid while causing minimal tissue damage.
Inside the patch are porous silica nanoparticles loaded with naloxone, a medication that blocks the effects of opioids. The openings of those nanoparticles are covered with fentanyl-sensitive molecular gates.
When fentanyl reaches the patch, it causes the gates to open, allowing naloxone to be released into the body. Higher fentanyl concentrations trigger the release of more medication. Because only some of the pores open during each response, the patch retains naloxone that can be released during future fentanyl exposure.
Penghui Zhao, the paper’s first author and a visiting instructor in Virginia Tech’s Academy of Integrated Science , led the development and testing of the patch.
“One of the greatest technical challenges was finding the right combination of biomaterials and microneedle technology to achieve reliable, on-demand drug release while maintaining mechanical strength, biocompatibility, and responsiveness,” Zhao said.
The repeated-release feature could be particularly important because the effects of fentanyl may last longer than those of naloxone. After an initial dose of naloxone wears off, overdose symptoms can return. The patch is designed to respond again if fentanyl levels remain high.
Sun describes the device as a harm-reduction tool rather than a replacement for pain medication or other medical care. Opioids are commonly prescribed for legitimate pain relief, and accidental overdoses can occur when someone becomes confused about whether a dose has already been taken.
“We expect an opioid concentration in the bloodstream because you need pain relief,” Sun said. “But we don’t want that to be too high. We designed the sensor to monitor the opioid concentration, and once it reaches a threshold, it triggers the release of an antagonist that can prevent overdose.”
Although the researchers used fentanyl and naloxone to demonstrate the system, Sun said the underlying chemistry could be adapted to recognize other opioids or release other drugs that block their effects.
The iNal patch is smaller than a penny. Photo courtesy of Penghui Zhao.
The researchers first tested the patch in laboratory settings to determine whether fentanyl would reliably trigger naloxone release. The system responded within minutes, released larger quantities of naloxone as fentanyl concentrations increased, and continued releasing medication for up to 24 hours.
They then evaluated the patch in mice. The patch released more naloxone as the fentanyl dose increased and continued to respond through at least three separate fentanyl exposures.
“The most exciting moment came from the animal studies,” Zhao said. “Seeing the patch respond to fentanyl exposure and effectively reverse opioid-induced effects showed us that the technology could potentially work beyond the laboratory.”
Mice treated with the patch showed substantially fewer opioid-induced symptoms than mice exposed to fentanyl without it.
The researchers found no significant signs that the patch caused irritation or other harmful effects. More research is needed, however, to understand how well it holds up over time, how consistently it works across different skin types and real-world conditions, and how accurately it can respond to different opioids.
The project began in 2022 and grew from Sun’s broader interest in engineering drug-delivery systems that respond to clinical challenges.
“I was looking for a challenge where engineering could make a real difference,” Sun said. “When I learned more about opioid overdose and how many lives it claims, I knew this was a problem I wanted to help solve.”
The study brought together researchers from biological systems engineering, the Virginia Tech College of Science , the School of Neuroscience , the University of Wisconsin–Madison, the University of California Riverside, and the University of Sydney. Zerui Zhou, a doctoral student in Sun’s lab, and Yuanzhi Bian, a BSE postdoctoral fellow, also contributed to the research.
Sun and Zhao have filed a patent application related to the technology. Sun is now exploring next steps to develop the patch into a product that could eventually be used beyond the laboratory.
“This is a very general platform,” Sun said. “It has a lot of opportunities.”
Original study : DOI 10.1002/advs.202524301
Advanced Science
A Fentanyl-Responsive Microneedle Patch for Harm Reduction
9-Jul-2026