Biodegradable polymersomes that can potentially be employed in drug delivery systems were fabricated by blending poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) (PLLA-PEG-PLLA) and poly(D-lactide)-b-poly(ethylene glycol)-b-poly(Dlactide) (PDLA-PEG-PDLA) block copolymers in a weight ratio of 1:1 in an aqueous solution. A series of amphiphilic PLLA-PEG-PLLA and PDLA-PEG-PDLA triblock copolymers were synthesized with different hydrophobic chain lengths through ring-opening polymerization. The self-assembly of pure PLLA-PEG-PLLA and an equimolar mixture of enantiomers of PLLA-PEG-PLLA and PDLA-PEG-PDLA was investigated by transmission electron microscopy, X-ray diffraction, and dynamic light scattering. Various nanostructures including spherical micelles, worm-like micelles, and vesicles were obtained by controlling the hydrophobic chain length and the incubation temperature. In the pure PLLA-PEG-PLLA systems, the hydrophobic−hydrophilic balance dominated the self-assembled morphologies. In equimolar enantiomer mixtures, self-assembled morphologies were greatly affected by the formation of the PLLA-PDLA stereocomplex (SC). There was an inverse correlation between the SC crystallinity and the curvature of the selfassembled structuresthe higher the SC content, the smaller the curvature. This rule was not applicable when the SC content was too high (≳50%), which produced spherical micelles as the main nanostructures. Since the SC-induced self-assembly could be controlled by changing the incubation temperature, the polymersomes can potentially be used in many applications, such as nanoreactors and nanovehicles.

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For applications in the fields of biological imaging and chemical sensing, fluorescent carbon nanodots (CNDs) have excellent possibilities because of their unique structure and performance. In this work, we synthesized a series of nitrogen-doped CNDs (N-CNDs) with different fluorescent emission, ranging from blue to yellow, via one-pot solvothermal strategy. Citric acid and urea were employed as the precursors. Formamide, ethanol and N,N-dimethylformamide were used as the solvent, respectively. The excitation-dependent emission and the optimal emission were measured with the ultraviolet–visible and photoluminescence spectra. The morphology and chemical structure of the prepared N-CNDs were characterized via high-resolution transmission electron microscope (HRTEM), atomic force microscope (AFM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, carbon nuclear magnetic resonance (13C NMR) spectroscopy, and so forth. The influence of reaction time, temperature, and type of solvent on the structure of N-CNDs were systematically investigated. The photoluminescence mechanism was discussed based on the chemical structure, the crystallinity and the sp2/sp3 carbon ratio of the prepared N-CNDs. In addition, a biocompatible amphiphilic copolymer mPEG-b-PLLA was synthesized and self-assembled in an aqueous system. The prepared N-CNDs were introduced into the polymer self-assemblies as a fluorescent probe by an in situ grafting method. The fluorescence imaging performance of N-CNDs in the polymer self-assemblies was investigated by comparing with organic fluorescent dye coumarin-6.

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