A versatile synthetic approach to tunable dual-emissive Pdots with very small-size based on amphiphilic block copolymers for cell imaging

Fluorescent polymer dots (Pdots) are a new type of efficient fluorophores with superior optical properties. However, their practical applications in bioimaging and biosensing are being hampered by their potential toxicity, poor water-solubility and the aggregation caused quenching effect. Herein, we report an effective strategy for the preparation of a series of new small-size aggregation-induced emission (AIE) active non-conjugated Pdots, which were self-assembled from three amphiphilic block copolymers, 4s-TPE-PCL-b-PNIPAM-Eu(III) (TPNE), 4s-TPE-PCL-b-PAA-Eu(III) (TPAE) and 4s-TPE-PCL-b-PVP-Eu(III) (TPVE). All of the blocks were synthesized by free-radical polymerization using a macroazoinitiator containing AIE fluorophore tetraphenylethene (TPE), poly(e-caprolactone) (PCL) segment and azo group, respectively. The obtained TPNE, TPAE and TPVE Pdots had small diameters down to 5 nm and good monodispersity. The Pdots not only exhibited well-separated dual-wavelength emission by 430 and 615 nm upon excitation at 360 and 395 nm, but also displayed thermo-tunable and pH-dependent fluorescence properties, excellent photostability, good water-solubility, good biocompatibility, favorable photoreversibility and noncytotoxicity. More interestingly, the as-prepared three kinds of Pdots displayed reversibly distinct dual-color (blue-red) fluorescence in the targeted three cancer cells (HepG2, A549 and HeLa cells) by merely tuning the excitation wavelength, indicating their potential applications as sensor and multicolour imaging agents in cell biology and diagnostics.