Toxicity of fluorescent silica nanoparticles in brine shrimp and their implications as food ingestion markers

Methods for observing zooplankton feeding are often limited by their small body size. Fluorescent silica nanoparticles (FSNPs) offer a promising alternative because of their bright fluorescence, photostability, and observability without the need for sophisticated equipment. To assess their potential as fluorescent markers, their physical properties, toxicity, and marking efficiency were ascertained using brine shrimp (Artemia franciscana) as a model marine zooplankton. The FSNPs were spherical, 64.0 ± 3.9 nm in diameter, and with stable dispersion in seawater. Acute toxicity tests showed no significant mortality or immobility in brine shrimp nauplii within 24 h of exposure to various FSNP concentrations. Ingested FSNPs exhibited bright luminescence along the gut passage under ultraviolet light, with marking efficiency increasing with FSNP concentration. An optimal concentration of 16 mg/L provided high fluorescence brightness without affecting locomotion or feeding rates. Food facilitated the clearance of FSNPs from the gut, and no observable FSNPs adhered to the outer surfaces of the shrimp. However, prolonged or repeated exposure to FSNPs at 16 mg/L reduced survival over time. These findings indicate that FSNPs are an effective, nontoxic marker for short-term studies of marine zooplankton feeding behavior, providing a valuable tool for ecological research.