Development of Biocompatible, UV and NIR Excitable Nanoparticles with Multiwavelength Emission and Enhanced Colloidal Stability

The development of functional nanoprobes for biomedical applications is highly important in the field of modern nanotechnology. Due to strict requirements, such as the ability to be excited using irradiation, which allows deep tissue penetration, nonblinking behavior, and good optical and colloidal stability, the choice of nanoparticles is limited, and their synthesis is challenging. Among all of the functional nanoprobes for biomedical purposes, upconverting nanoparticles, especially those with more complex architectures (e.g., core–shell or core–shell–shell), are the most promising candidates. This study demonstrates advanced synthetic routes for constructing biocompatible nanoprobes with tunable optical properties and colloidal stability. The core–shell–shell architecture of the nanoprobes allows excitation from at least four sources, such as 272 and 394 nm of near-ultraviolet (near-UV) irradiation and 980 and 808 nm near-infrared (NIR) lasers. Furthermore, Gd-matrix-based nanoprobes doped with lanthanide ions (Nd³⁺, Yb³⁺, Tm³⁺, and Eu³⁺) are known for their paramagnetic properties for magnetic resonance imaging (MRI) imaging as well as upconversion luminescence with diverse emission bands across the entire visible spectrum. This feature is highly desirable for photodynamic therapy applications, as the upconversion emission of the proposed nanoprobes could overlap with the absorption band of commonly used photosensitizers and could potentially result in an efficient energy transfer process and enhanced generation of reactive oxygen species or singlet oxygen.