N₂-BET is a Proxy for Primary Particle Size and May Not Be Representative of Available Specific Surface Area for Aggregated Nanoparticle Aerosols

The knowledge of the specific surface area of aerosolized engineered nanoparticles could be important for mechanistically understanding their toxic potential or functional characteristics. The most widely method to perform this measurement, N₂-BET, however, may not accurately represent the available surface area for hetero-aggregated nanoparticles in the context of large biological molecules. This study conducted an analysis of published characterization measurements including primary particle size, aggregation state, and specific surface area made for dry aerosolized nanoparticles. Results indicate that primary particle size explains 65% of the variance in specific surface area, while aggregation (as measured by mass median aerodynamic diameter) only explains 20% of the variance. Curiously, increasing aggregation (larger MMAD) is associated with increasing SSA as measured by N₂-BET, likely an artifact of the measurement method, which suggests that this technique may not be appropriate for studies investigating biological interactions with nanoparticles.