Injection Force Effects on Propidium Iodide Uptake in Nanoinjected HeLa Cells

The ability to deliver DNA sequences and molecular loads into the nucleus of a cell is a large area of interest in the medical community, and has numerous applications including gene therapy. Different methods of gene delivery each have their own advantages and disadvantages. Experimentation was performed using a new technique called nanoinjection to determine how force affects the efficiency and viability of the injection process. Nanoinjection, which utilizes an array of millions of solid microlances made on a 2 cm square silicon chip to inject cells, allows us to inject hundreds of thousands of cells at a time with high efficiencies. The solid nature of the lances allows them to be smaller, increasing cell viability. HeLa cells were used for testing in conjunction with an injection device that allowed for precise control of the injection force. Propidium iodide (PI), a dye that fluoresces when bound to DNA and doesn’t penetrate the membrane of living cells, was injected to monitor the efficiencies of transporting molecular loads across the cell membrane. The data was normalized to the controls for both efficiency (PI uptake) and viability to make it easier to see and determine trends. Results indicate a slow rise in injection efficiency from 0 to 1.8 Newtons of force where it reaches a maximum efficiency of 4.11 when normalized to the PI uptake of the positive controls. The data then levels, averaging an efficiency of approximately 3.1. The slow rise is likely due to more of the cells being punctured as the force increases until most have been punctured and the efficiency levels off. Viability had no clear trend, only varying between 0.97 and 1.04 when normalized to the viability of the negative controls.