Towards Designing Green-Inspired Nano- and Microemulsions Alongside Novel Solvatochromic Probes as an Effective Tool in Delivery Issues

The extensive use of submicron emulsion systems, particularly those stabilized by nonionic surfactants, with their proven effectiveness and safety profile, provides a reassuring foundation for our research. Consequently, we designed and engineered new submicron emulsion formulations stabilized with a biocompatible surfactant polyoxyethylated cocoamine, whose nonionic character is due to a high degree of polyoxyethylation. We chose oleic acid as the oil phase, a fatty acid known for its beneficial properties. This led to novel biocompatible nanoemulsions with high stability and cosurfactant-free microemulsions. The dynamic light scattering studies confirmed that both formulations have a nanometric size and low polydispersity index values. Moreover, transmission electron microscopy verified the nanodroplets' morphological homogeneity and spherical shape. The resulting nanoplatforms can be applied to carry bioactive agents in the pharmaceutical and cosmetic fields. For this reason, we solubilized newly synthesized 5-dimethylamino-5'-nitro-2,2'-bithiophene as a model hydrophobic cargo for delivering poorly water-soluble compounds. This dye was chosen due to its strong solvatochromic behavior and suitability for micropolarity analysis via UV-Vis spectroscopy. We also present a simple method for rapid micropolarity screening to assess the type of nanodispersion via solvatochromic shift as an alternative procedure for evaluating of the oils used to fabricate nanoformulations for pharmaceutical and cosmetic purposes.