Encoding microspheres based on fluorescence energy transfer between poly(phenylenevinylene) nanoparticles and rhodamine 6G

Highlights: • The microspheres were encoded with conjugated polymer nanoparticles and dye. • Energy transfer was employed to tune multiple emission at single excitation. • Protective layer prevented the variation of codes carried by the microspheres. • Distribution of fluorophores affected the efficiency of fluorescence energy transfer. Fluorescence-encoded microspheres are largely demanded in high-throughput assays. A strategy for preparing encoded microspheres based on fluorescence resonance energy transfer (FRET) was advanced. Two fluorophores, poly(phenylenevinylene) nanoparticles (PPV NPs) as the donor and rhodamine 6G (R6G) as the acceptor were employed to construct the energy-transfer pair, and introduced onto the substrate polymeric microspheres. The fluorescence intensity ratio between PPV NPs and R6G molecules were tuned based on energy transfer mechanism. Nine codes (wavelength-intensity combinations) were obtained at the same excitation by keeping the concentration of PPV NPs constant and varying the concentration of R6G in the dipping solutions. Then, a melamine–formaldehyde (MF) resin layer was coated onto the encoded spheres to prevent the leakage of fluorophores. The encoded spheres were found to have good fluorescence stability against various solvents and even "dissociation agent", and no significant variation of the codes were observed. Further modification of this MF layer with silanization reaction provided the amino reactive sites. In all, this study provides a general strategy for the preparation of fluorescence encoded microspheres based on energy transfer as well as a stable protective layer with reactive sites.