Jetting microfluidics with size-sorting capability for single-cell protease detection.

Activated proteases such as matrix metalloproteinases (MMPs) secreted from cancer cells can degrade the extracellular matrix (ECM) and contribute to tumour formation and metastasis. Measuring MMP activity in individual cancer cells can provide important insights on cancer cell heterogeneity and disease progression. Here, we present a microfluidic platform combining a droplet jetting generator and a deterministic lateral displacement (DLD) size-sorting channel that is capable of encapsulating individual cancer cells inside picoliter droplets effectively. Droplet jetting with cell-triggered Rayleigh-Plateau instability was employed which produced large droplets capable of cell encapsulation (diameter, ~25µm) and small empty droplets (diameter, ~14µm), which were then size-separated using a DLD size-sorting channel to enrich the single-cell encapsulated droplets (~78%), regardless of the cell density of input sample solutions. The droplets containing encapsulated cancer cells were collected in an observation chamber to determine the kinetic profiles of MMP secretion and the inhibitory response in the presence of the drug doxycycline at the single-cell level to reveal their heterogeneous MMPs secretion activities.