Divalent cations accelerate aggregation of Black phosphorus nanodots

Abstract

Abstract Black phosphorus (BP) nanodots inevitably interact with electrolyte ions because of their extensive applications in many fields. In biomedical applications, BP-nanodots might encounter various salt ions in body fluids and have a propensity to aggregate, further resulting in an enhanced toxicity risk. In this study, the effects of electrolyte cations (Na+, K+, Ca2+, and Mg2+) on the aggregation kinetics of BP-nanodots were investigated by means of dynamic light scattering (DLS). The critical coagulation concentration values of BP-nanodots were determined to be 242.11 mM NaCl, 95.01 mM KCl, 1.92 mM CaCl2, and 5.88 mM MgCl2. Divalent cations accelerated aggregation of BP-nanodots because of the stronger surface charge screening and their bridging with oxidized phosphorus species (PxOy) available on BP-nanodot surfaces. Furthermore, the divalent cations may interact with PxOy to form insoluble complex coatings on the nanoparticle surface and shield the charge. After modification with PEG, BP-nanodots presented enhanced stability in the presence of 2.5 mM CaCl2. This work is of great significance for understanding the aggregation behaviors of ultrasmall nanoparticles such as BP-nanodots in electrolyte solutions and provides insight into their safety assessment associated with biomedical applications.