Solid Lipid Nanoparticles in Imaging, Diagnostics and Theranostics: A Review of a decade of Innovations and Clinical Applications

The clinical demand for safer, more precise, and functionally versatile imaging tools has intensified with the increasing complexity of disease diagnosis and management. Despite major strides in imaging technologies such as MRI, CT, USG, and PET/SPECT, many modalities are grappled by issues including low specificity, high systemic toxicity of contrast agents, and limited ability to provide real-time functional data. Dreaded by these shortcomings, nanotechnology-based approaches such as liposomes, quantum dots (QDs), polymeric nanoparticles (NPs), gold NPs, lipid NPs, and metallic NPs have emerged as promising alternatives. Among these, solid lipid nanoparticles (SLNs) offer a unique combination of biocompatibility, structural versatility, and surface functionalizability, positioning them as advanced carriers for next-generation imaging as well as diagnostic applications, alike. SLNs are a promising nanoplatform for the delivery of imaging and diagnostic agents owing to their biocompatibility, diversity in payload encapsulation, tunable surface properties, and potential for targeted delivery. They can enhance sensitivity and specificity across imaging modalities such as MRI, PET/SPECT, CT, and optical imaging across multiple disease states. However, despite encouraging preclinical results, SLNs still face challenges such as stability, toxicity, reproducibility, and regulatory standardization, which deter their clinical application. Future research should focus on developing multifunctional SLNs for multimodal imaging, ensuring robust safety data, and concordance with regulatory standards. The integration of diagnosis and therapy, particularly in oncology, will be pivotal. Additionally, personalizing SLNs through ligand targeting may enhance their clinical feasibility and effectiveness.