Low-cost highlighter nanoparticles for highly efficient multistep excitation energy transfer

Efficient excitation energy transfer (EET) is essential for energy harvesting, optoelectronics, luminescence bioimaging and photothermal medicine. Recent advances in optimised multistep EET systems have expanded the potential of these applications, offering large Stokes shifts, long-range energy transfer, and a broader tuning range for excitation and emission. However, the energy transfer efficiency of these systems rarely exceeds 90%, suggesting room for further improvement. Seeking low-cost solutions to this global problem, we show that a worldwide commercial orange highlighter ink produces both direct and multistep EET with near-unity efficiency (94.4%) among the highest recorded in the literature. We reveal that this efficiency results from a stable monodisperse dispersion of dye-loaded polymer nanoparticles in a water-glycerol medium. We identified the main dyes involved, elucidated the two-step energy transfer sequence, and demonstrated that orange highlighter particle dispersions can serve as an efficient water-ethanol sensor through monitoring variations in EET efficiency. This work presents a low-cost and readily available material exhibiting exceptionally high multistep EET efficiency, offering broad application potential.