Biomedical applications of lignin nanoparticles and their nanoconjugates: Advancements in synthesis, therapy, imaging, and drug delivery.

Multidrug resistance (MDR) in cancer and infectious diseases is a major global challenge. It reduces the effectiveness of antibiotics and chemotherapeutics, leading to higher treatment costs and mortality. Conventional agents suffer from poor selectivity, systemic toxicity, and resistance linked to efflux pump overexpression. This review addresses how lignin nanoparticles (LNPs) and their nanoconjugates can provide relatively sustainable, biocompatible alternatives to overcome MDR through tunable surface chemistry, stimuli responsiveness, and multifunctionality. Developments in LNP synthesis using various methods enable control over size, charge, and morphology for optimised biological performance. Functionalisation or conjugation of lignin with different materials has yielded systems capable of imaging and treatment via diverse mechanisms. Emerging designs such as lignin hollow nanoparticles enhance drug loading and release efficiency, while ultrasmall lignin-derived quantum and carbon dots highlight promise as fluorescent probes for real-time bioimaging, photodynamic therapy, and theranostic applications. These multifunctional LNPs exhibit low cytotoxicity, high stability, and precise biodistribution, highlighting their potential for targeted and image-guided therapy. This review elucidates the synthesis-structure-activity relationships influencing lignin-based nanomaterials and highlights their promise as eco-friendly, multifunctional nanoplatforms for next-generation biomedicine.