UV-induced autofluorescence enhancement improves imaging of single polystyrene nanoparticles.

Detection of polymer nanoparticles remains challenging due to their weak optical contrast. Here, we demonstrate that UV illumination can be exploited to enhance their intrinsic autofluorescence, enabling the optical detection of polystyrene (PS) nanoparticles of 100 nm diameter with a simple and cost-effective UV microscope. Contrary to the expected photobleaching behavior, the autofluorescence intensity of PS nanoparticles increases markedly during continuous UV exposure. This enhancement arises from the nanoparticle surface photodecomposition mediated by reactive oxygen species (ROS), exposing fresh emissive PS domains. Complementary experiments using antioxidants and controlled oxidizing environments confirm the central role of ROS in this phenomenon. The resulting autofluorescence gain significantly improves the limit of detection and enables reliable discrimination between polymer and metal nanoparticles. This photoactivation mechanism provides a powerful new route for high-sensitivity detection of polymer-based nanoparticles using simple optical setups, unlocking potential applications in analytical chemistry, biosensing, and environmental monitoring.