Cucurbiturils (CBs) of the appropriate size (CB[7] and CB[8]) form strong guest–host complexes in phosphate buffer solution (PBS) with acridine orange (AO) and pyronine Y (PYY) with 1 : 1 and 2 : 1 stoichiometries for CB[7] and CB[8] complexes, respectively. Binding constants in the range 0.87–1.60 × 10⁶ M⁻¹ and 5.2–6.3 × 10¹³ M⁻² were determined by titration with fluorescence spectroscopy for 1 : 1 and 2 : 1 complexes, respectively. These binding constants in PBS and the eight-fold excess of CBs minimize the presence of free dye in solution and also stabilize the host–guest complex in the culture medium. Images showing that the CB complexes can cross the cell membrane of 3T3 cells have been acquired using fluorescence microscopy. Given the current importance of supramolecular CB complexes and the search for new drug delivery systems, the present findings open avenues for the use of CBs as nanocapsules to transport drugs into the cells.

Nanomaterials are proving useful for regenerative medicine in combination with stem cell therapy. Nanoparticles can be administrated and targeted to desired tissues or organs and subsequently, be used in non-invasive real-time visualization and tracking of cells by means of different imaging techniques, they can act as therapeutic agent nanocarriers, and can also serve as scaffolds to guide the growth of new tissue. Nanoparticles can be of different chemical nature, such as gold, iron oxide, cadmium selenide, and carbon, and have the potential to be used in regenerative medicine. However, there are still many issues to be solved, such as toxicity, stability, and resident time. Upconversion nanoparticles have relevant properties such as: i) low toxicity, ii) capability to absorb light in an optical region where absorption in tissues is minimal and penetration is optimal (note they can also be designed to emit in the NIR region), and iii) they can be used in multiplexing and multimodal imaging. An overview on the potentiality of upconversion materials in regenerative medicine is given.

Ablated, “pseudo-naked” gold nanoparticles (AuNPs) catalyze the cis–trans isomerization of substituted azobenzenes. para-Substitution was found to affect the rate of isomerization, suggesting the participation of AuNP-mediated electron transfer in the isomerization mechanism.