Functional lysosomal probes from pH sensing and enzyme activation to targeted nanoplatforms.

Lysosomes are acidic, enzyme-rich organelles that regulate macromolecular degradation, nutrient sensing, and intracellular signaling, and their dysfunction is linked to neurodegeneration, cancer, infection, and lysosomal storage disorders. This review surveys recent progress in lysosome-targeted fluorescent probes and related functional platforms. Three major classes are considered: pH-sensitive probes, enzyme-activated probes, and targeted nanoparticles or ligand conjugates. Across these categories, the field is evolving from simple lysosomal labeling toward quantitative and biologically informative systems, including ratiometric sensors, near-infrared and two-photon fluorophores, super-resolution-compatible probes, and theranostic constructs. We also compare the principal targeting mechanisms, including pH-dependent ion trapping, receptor-mediated endocytosis, and passive endocytic accumulation. Key limitations remain off-target localization, enzyme cross-reactivity, fluorophore leakage, formulation variability, and biosafety concerns. Future progress will depend on improving quantitative reliability, minimizing organelle perturbation, and validating these platforms in disease-relevant and clinically meaningful biological models for diagnosis, mechanistic studies, and therapeutic development across lysosome-associated diseases in vivo models.