This thesis investigates the development and application of advanced nanoparticle systems for targeted theranostic purposes, with an emphasis on cancer and infectious diseases. Each chapter offers unique insights and substantial contributions to the field, demonstrating the potential of nanotechnology in precision medicine. Chapter 2 presents a bibliometric and scientometric analysis of PSMA-targeted radiotheranostics, mapping out research growth over the past decade. The analysis covers over 600 peer-reviewed studies and identifies leading contributors and key institutions that have shaped the field. This chapter's main contribution lies in establishing a knowledge base that highlights the collaborative nature and evolving focus areas of PSMA-related research. Chapter 3 reviews the evolution of PSMA-targeted radiotheranostics and its integration into nuclear medicine. The chapter concludes that PSMAtargeted ligands have improved prostate cancer diagnosis and treatment, with clinical trials demonstrating enhanced specific binding and therapeutic response rates. A significant highlight is the increased use of alpha-emitting radionuclides, which have shown superior results in precision therapy compared to conventional beta-emitters. Chapter 4 focuses on the synthesis and application of Lanthanide-Based Unified Nanoparticle Assemblies (LUNA), showcasing a one-step synthesis method that yields stable and highly specific nanoparticles. Characterization results indicate that LUNA achieves consistent size distribution (approximately 100 nm) and demonstrates strong photoluminescent properties, making it suitable for combined imaging and treatment. This chapter contributes to advancing multifunctional nanoparticle design for targeted theranostic use. Chapter 5 introduces ExoFlocs, a self-assembled coordination polymer nanoparticle system designed for the rapid and selective capture of small extracellular vesicles (sEVs). The study highlights an isolation efficiency of up to 75%, significantly reducing processing time compared to ultracentrifugation. The chapter emphasizes how ExoFlocs enhance the precision of liquid biopsy techniques and enable better analysis of biomarkers for disease monitoring. Chapter 6 discusses the creation of Ultra-Stable Gold Nanoparticles (USAuNPs) for diagnosing vaginal candidiasis, featuring a pH-assisted synthesis method that promotes biocompatibility. The chapter underscores the development of a colorimetric assay capable of detecting Candida albicans within 30 minutes, demonstrating a high diagnostic accuracy rate. This work's main contribution is presenting a cost-effective, point-of-care diagnostic tool that can be adapted for low-resource settings. The final chapter consolidates the thesis's findings and emphasizes the overarching impact of integrating green chemistry principles and interdisciplinary approaches in nanoparticle synthesis. This research demonstrates that using eco-friendly, scalable nanoparticle synthesis methods can lead to significant advancements in medical diagnostics and treatment, with potential applications that extend from oncology to broader public health initiatives.