An Acoustic Droplet-Induced Enzyme Responsive Platform for the Capture and On-Demand Release of Single Circulating Tumor Cells

The recovery of rare single circulating tumor cells (CTCs) from patients has great potential to facilitate the study of cell heterogeneity and cancer metastasis, which may promote the development of individualized cancer immunotherapy. Herein, a versatile single-cell recovery approach that utilizes an acoustic droplet-induced enzyme responsive platform for the capture and on-demand release of single CTCs is proposed. The platform combines a multifunctional enzyme-responsive gelatin nanoparticle (GNP)-decorated substrate (GNP-chip) for specific capture with an acoustic droplet positioning technique to realize on-demand release of single CTCs. The acoustic droplet dispenser is employed to generate oxidized alginate microdroplets containing the MMP-9 enzyme (OA-MMP-9) with controllable size and precise positioning upon the cell-attached GNP-chip, allowing controlled cell-surface biodegradation under enzymatic reactions followed by calcium chloride (CaCl2) solution treatment to form single-cell encapsulated calcium alginate hydrogels. Benefitting from the existence of hydrogels, the released cells could be efficiently recovered by microcapillary. Results demonstrate that the encapsulated cells maintain good cell morphology in the hydrogels, which allow further single-cell nucleic acid analysis. As a proof-of-concept platform, this approach enables reliable and efficient retrieval of single CTCs and holds the potential for versatility in single-cell analysis systems.