Dynamic Phosphate Hydrogen‐Bonded Networks Enable Biomedical‐Ready Stabilization of Black Phosphorus

ABSTRACT Black phosphorus (BP) has emerged as a promising nanomaterial for biomedical applications such as photothermal therapy and drug delivery, owing to its biocompatibility and tunable biodegradability. However, its practical use is severely limited by rapid oxidative degradation in aqueous environments. Here we report an unconventional passivation strategy in which standard, biocompatible saturated phosphate‐buffered saline (PBS) stabilizes BP through the in situ assembly of a dynamic phosphate hydrogen‐bonded network at the solid–liquid interface. Mild surface oxidation of BP initiates hydrogen‐bond interactions with phosphate species, which spontaneously self‐organize under high phosphate concentrations. This adaptive network thermodynamically suppresses oxygen and water adsorption without permanent modification or coatings. As a result, BP exhibits long‐term stability in saturated PBS while retaining its intrinsic functional properties. Since PBS is a classical buffer in biomedicine, the stabilized dispersions require no separation or purification, allowing direct dilution for biomedical use. Beyond BP, this work suggests that phosphate hydrogen‐bonded network engineering can serve as a generalizable strategy for stabilizing diverse two‐dimensional materials in complex aqueous environments.