Micro and nanoplastics have become increasingly relevant as contaminants to be monitored due to their potential health effects and environmental impact. Nanoplastics, in particular, have been shown to be difficult to detect in drinking water, requiring new capture technologies. In this work, we applied the acoustofluidic seed particle method to capture nanoplastics in an optimized, tilted grid of silica clusters even at the high flow rate of 5 mL/min. Moreover, we achieved, using this technique, the enrichment of nanoparticles ranging from 500 nm to 25 nm as a first in the field. We employ fluorescence to observe the enrichment profiles according to size, using washing buffer flow at 0.5 mL/min, highlighting the size-dependent nature of silica seed particle release of various sizes of nanoparticle. These results highlight the versatility of acoustic trapping for a wide range of nanoplastic particles and allow further study into the complex dynamics of the seed particle method at these size ranges. Moreover, with reproducible size-dependent washing curves, we provide a new window into the rate of nanoplastic escape in high-capacity acoustic traps, relevant for both environmental and biomedical applications.