Electrospray at minimum flow rate produces a jet thinner than a cell. This is the enabling condition for single-cell deposition: because the jet is narrower than the object it carries, individual cells can be visually detected during transit and placed at user-defined locations.
The counterintuitive move is operating at the stability limit rather than above it. Higher flow rates give a thicker, more stable cone-jet with higher throughput. But higher throughput means cells arrive in groups, unsorted, unresolvable. The minimum flow rate sacrifices throughput for resolution — each cell transits the jet individually, visible against the thinner stream.
Cell damage is largely reversible. Membrane integrity is maintained after exposure to the electrosprayed liquid, suggesting that the electric field and shear forces at these flow rates perturb the cell without permanently disrupting it. The cells survive the passage through a jet that is thinner than they are, which requires temporary deformation.
The technique works at elevated cell concentrations, not just dilute suspensions. This matters because serial dilution to achieve single-cell isolation is wasteful and slow. A jet that is thinner than a cell achieves spatial resolution without dilution — the geometry of the channel does the sorting.
The general principle: resolution in placement comes from making the delivery channel smaller than the object being delivered. The cell becomes its own bottleneck, and the bottleneck becomes a feature.