Fentanyl is one of the more deadly synthetic opioids because it’s both potent and hydrophobic. It can easily slip into the body’s fat tissue and lurk there, releasing slowly over several hours to cause an overdose. The opioid overdose antidote naloxone can fight fentanyl, but its power is short lived; the body metabolizes naloxone in about an hour. Seeking to make a longer-lived opioid overdose antidote, chemists at the Allegheny Health Network Research Institute and Duquesne University covalently linked naloxone to poly(lactic acid) (shown) and then formulated the resulting polymer into nanoparticles. These nanoparticles slowly release naloxone as esterase enzymes cleave it from the poly(lactic acid). By changing the size of the nanoparticles, the chemists can tune the time it takes to release the overdose antidote, said AHN Research Institute’s Saadyah Averick, who presented the work at the ACS national meeting. In tests with mice, these nanoparticles block the effects of morphine for up to 96 h. Next, the researchers plan to see how effectively the nanoparticles block fentanyl.