Figure 1: Schematic of the nanoneedle array-based intracellular delivery system.

(a) Illustration of the basic design and working principle. (b) The work flow of the delivery procedures using nanoneedle arrays. The interaction between nanoneedles and cells was precisely controlled by centrifugation-induced supergravity to achieve reliable and efficient cytosolic delivery. Briefly, the culture medium was first removed, and replaced with basal medium containing materials to be delivered (fluorescent dye, dextran, antibody, nanoparticle, DNA, and so on). The solution volume was just enough to cover all the cells and to prevent cells from drying. A nanoneedle array was then placed onto the solution with nanoneedles facing towards cells, leaving a thin layer of solution between the nanoneedles and the cells. The whole setup was placed in a centrifuge and spun at various speeds. After centrifugation, extra basal medium (containing cargo materials at desired concentrations) was immediately added to the culture well to lift off the nanoneedle patch. After 5–30 min incubation at 37 °C, fresh culture medium was used to wash off extra materials and to culture the cells for further analysis. The nanoneedle patch was then cleaned with piranha solution for reuse.