An automated nanoinjection system has been developed and tested for the delivery of propidium iodide into culture cells. Nanoinjection is the process by which molecules are delivered into living cells using a solid needle. Propidium iodide, a dye that fluoresces when bound to nucleic acids, was used as the injection molecule to monitor nanoinjection efficiency. The nanoinjection system uses a programmable microcontroller to manipulate a linear actuator, which presses a silicon lance array into thousands of living culture cells simultaneously. The lances penetrate cell membranes, allowing dye molecules to enter the cell through membrane pores opened by lances. The system was developed to apply the same injection force to each cell sample at the press of a button, eliminating any experimental variability in data due to the operator. Tests were performed at a dye concentration of 0.04 mg/mL for all experiments. Several forces were tested to determine the optimal nanoinjection force needed for maximum dye delivery. We found the optimal force range to be 8.8–14.7 N. The average PI uptake into cells at a force of 8.8 N and 14.7 N is 57.6±7.7% and 60.3±6.6%, respectively. Previous studies with a manual injection force have shown average propidium iodide uptake to be 60.4±18.0%. High cell viability is maintained with the automated nanoinjection system. At all forces applied in this experiment, an average of 78% or greater viability was observed. With the data gathered in this experiment, we conclude that the automated nanoinjection system eliminates much of the uptake efficiency variability inherent to nanoinjections performed with a manual injection force.
