A novel label-free carbon dots-based fluorescent aptamer sensor for the detection of fentanyl

Fentanyl, a widely abused potent synthetic opioid, poses a challenge due to its narrow therapeutic window, increasing the risk of overdose and death. Fast, easy, and cost-effective screening for fentanyl in biological samples is crucial for forensic and public safety purposes. We hereby present a label-free fluorescence sensor for the precise and sensitive identification of fentanyl, utilizing carbon dots (CDs) in conjunction with aptamers. By synthesizing green-emitting CDs in a single step using an environmentally friendly method with o-phenylenediamine (OPD) and thiourea in acetone, the CDs displayed excellent optical properties and biocompatibility. Due to the positive charge of CDs, their fluorescence quenching is caused by electrostatic interactions with negatively charged aptamers. When fentanyl is introduced, the specific binding between fentanyl and the fentanyl aptamer is strengthened, resulting in fluorescence recovery. Under optimal experimental conditions, there was a linear relationship between fluorescence intensity and fentanyl concentration in the 5–1000 nM with a limit of determination of 1.90 nM. The robust quantification of fentanyl in complex human saliva matrices achieved by this aptamer-based biosensing platform validates its clinical reliability, particularly for non-invasive point-of-care monitoring and harm-reduction interventions in opioid crisis management.