Full-color tunable organic nanoparticles with FRET-assisted enhanced two-photon excited fluorescence for bio-imaging

Two-photon excited fluorescence (TPEF) bio-probes are important for tissue imaging. Here, we demonstrated a strategy for highly emissive, photostable, low cytotoxicity and full-color tunable TPEF organic nanoparticles (ONPs) comprising of commercially available dyes doped in a TPEF host matrix. Because of efficient Forster resonance energy transfer (FRET), near-IR laser pumping light can be strongly absorbed by host matrix molecules via a two-photon absorption (TPA) process and transferred to dopant dyes, which then emit visible photons in different colors from blue, green, and yellow to red with high quantum yields. Our strategy significantly enhanced the photo-stability and TPEF of dopant dyes in ONPs, avoiding the need to resort to specially engineered expensive dyes.