Complex coacervates enable microRNA concentration for direct nanopore detection

Complex coacervates (CCs) effectively concentrate biomolecules via liquid-liquid phase separation; however, extracting analytes for detection remains challenging because of the high ionic strength required to dissolve the CC phase. Here, we demonstrate a workflow integrating CC-based pre-concentration with nanopore sensing, which inherently operates under high-salt conditions. We investigated CCs formed by polycations (PLL, PDDA) and nucleotides (ATP, ADP) for the enrichment of microRNAs (miRNAs). While these CC components inhibited reverse-transcription polymerase chain reaction (RT-PCR), the dissolved phase was compatible with lipid bilayer-based α-hemolysin nanopore detection. Optimization of the polymer composition (S-PDDA/ATP) minimized pore clogging and noise. Using specific DNA probes, we successfully detected miRNA enriched in the CCs immediately after salt-induced dissolution. This study establishes a proof of concept for using phase separation as a seamless pre-concentration strategy for nanopore-based biosensing.