Chemical design principles for Janus nanoparticles: Controlling surface anisotropy for precision delivery and diagnostics

Janus nanoparticles (JNPs), with their spatially distinct chemical domains, represent a powerful platform for engineering multifunctional interfaces at the nanoscale. This review explores the chemistry that governs their design—focusing on how surface anisotropy enables orthogonal reactivity, directional assembly, and environment-specific interactions in biological systems. We analyze key synthetic approaches such as interfacial polymerization, Pickering emulsions, and surface-directed phase separation, highlighting how chemical asymmetry can be tuned for targeted delivery, molecular imaging, and biosensing. Beyond summarizing current strategies, we propose a framework connecting interfacial chemistry to functional output, offering insight into how Janus design principles can be chemically programmed to address limitations in precision therapeutics and diagnostics. We also outline future challenges in scalability, ligand compatibility, and interface predictability, advocating for a chemistry-first approach to next-generation JNP systems. By linking molecular design to functional behavior, this review aims to catalyze innovation in chemically tailored nanomaterials for biomedical and beyond.