Large-Area Silicon Nitride Nanosieve for Enhanced Diffusion-Based Exosome Isolation

Nanoporous membranes have a variety of applications, one of which is the size-selective separation of nanoparticles. In drug delivery, nanoporous membranes are becoming increasingly important for the isolation of exosomes, which are bio-nanoparticles. However, the low pore density and thickness of commercial membranes limit their efficiency. There have been many attempts to fabricate sub-micrometer thin membranes, but the limited surface area has restricted their practicality. In this study, large-area silicon nitride nanosieves for enhanced diffusion-based isolation of exosomes are presented. Notably, these nanosieves are scaled to sizes of up to 4-inch-wafers, a significant achievement in overcoming the fabrication challenges associated with such expansive areas. The method employs a 200 nm porous sieve (38.2% porosity) for exosome separation and a 50 nm sieve (10.7% porosity) for soluble protein removal. These 300 nm thick nanosieves outperform conventional polycarbonate membranes by being 50 times thinner, thereby increasing nanoparticle permeability. The method enables a 90% recovery rate of intact exosomes from human serum and a purity ratio of 3 × 10⁷ particles/µg protein, 4.6 times higher than ultracentrifugation methods. The throughput of the method is up to 15 mL by increasing the size of the nanosieve, making it an ideal solution for large-scale exosome production for therapeutic purposes.