Acoustofluidic enrichment of small extracellular vesicles: physical principles, microfluidic implementations, and prospects for Parkinson's disease liquid biopsy.

Reliable blood-based small extracellular vesicle (sEV) analysis for Parkinson's disease (PD) is constrained by co-isolation of lipoproteins and proteins from plasma. This review examines acoustofluidics as a sample-preprocessing and integration-enabling strategy for PD liquid biopsy. We first summarize the analytical value and limitations of sEV-associated α-synuclein, microRNA panels, and multi-omics cargo, and then compare conventional and microfluidic enrichment methods with particular attention to lipoprotein co-isolation, recovery, fraction purity, throughput, and compatibility with downstream assays. We further analyze the physical basis of acoustofluidic separation, including particle volume, density, compressibility, and acoustic contrast factor, and assess its potential integration with on-chip lysis, nucleic acid amplification, protein assays, and signal readout. Current evidence suggests that acoustofluidics can provide label-free, noncontact enrichment of sEV-containing fractions while offering a physical separation dimension complementary to size and buoyant density. However, it achieves reduced lipoprotein co-isolation rather than complete removal, yielding sEV-enriched fractions rather than highly pure isolates. Clinical translation will therefore require standardized pre-analytical workflows, explicit reporting of sEV recovery and lipoprotein depletion, demonstration that improved fraction quality enhances biomarker measurement, and prospective multicenter validation. Acoustofluidics should thus be viewed as a promising front-end technology for improving the analytical reliability and integration of PD sEV liquid biopsy rather than as an independent diagnostic method. The critical question remains whether improved sEV enrichment can ultimately translate into more reliable and clinically useful PD biomarker measurements. We use sEV terminology without assuming endosomal origin.