Microfluidic Crystallization of Surfactant-Free Doped Zinc Sulfide Nanoparticles for Optical Bioimaging Applications

The room-temperature controlled crystallization of monodispersed ZnS nanoparticles (average size of 5 nm) doped with luminescent ions (such as Mn$^{2+}$, Eu$^{3+}$, Sm$^{3+}$, Nd$^{3+}$, and Yb$^{3+}$) was achieved via a microfluidic approach. The preparation did not require any stabilizing ligands or surfactants, minimizing potential sources of impurities. The synthesized nanomaterials were characterized from a structural (XRD and XAS at lanthanide L$_{3}$ edges), morphological (TEM), and compositional (XPS, ICP-MS) perspective, giving complementary information on the materials’ features. In view of potential applications in the field of optical bioimaging, the optical emission properties of the doped nanoparticles were assessed, and samples showed strong luminescent properties while being less affected by self-quenching mechanisms. Furthermore, in vitro cytotoxicity experiments were conducted, showing no negative effects and evidencing the appeal of the synthesized materials for potential applications in the field of optical bioimaging.