The self-fluorescence verification and intracellular imaging of nanocrystals imbedded with aggregation-induced emission luminescent materials

Understanding cellular uptake and intracellular dissolution of drug nanocrystals is necessary. Due to their superior sensitivity, luminescent materials with aggregation-induced emission (AIE) are embedded into drug nanocrystals (hybrid nanocrystals) as a good strategy for tracking intact nanocrystals in cells. However, AIE materials are strongly hydrophobic and tend to self-aggregate, generating fluorescent interference. To exclusively mark nanocrystals, AIE materials must be embedded in nanocrystals and remain soluble when released from dissolved nanocrystals. In this study, cyclosporin A (CsA) nanocrystals (CsA/THPE NCs) embedded with tetrakis(4-hydroxyphenyl)ethylene (THPE) possessing AIE properties were prepared. The self-fluorescence of CsA/THPE NCs was collectively corroborated by scanning electron microscopy, powder X-ray diffraction, fluorescence microscopy, and dissolution experiments. During the dissolution test, CsA/THPE NCs showed a certain degree of slow-release property. Cellular uptake studies were conducted with Caco-2 cells and characterized by confocal microscopy, flow cytometry, and quantitative analyses. The intact nanocrystals could be directly taken up by cells. The cellular uptake was found to be concentration- and time-dependent. Based on the above experimental results, hybrid nanocrystals integrated with AIE materials were verified to have specific self-fluorescence. Additionally, the dissolution rate of nanocrystals can be adjusted by physically embedding them with other materials.