Figure 1. Modified capillary gun apparatus. A: The modified capillary gun was constructed according to the schematic shown above. B, C: The gun’s nozzle is made up of a blunted Luer lock disposable needle (18 gauge), plastic T-connector, and gel loading pipette tip, assembled as shown in the diagram. As described in more detail in the text, low-pressure helium flow is used to accelerate aliquots of DNA-coated gold microparticles suspended in ethanol that are injected into the head of the needle. As the microparticles emerge from the tip of the blunted needle, a vacuum flow is used to divert the bulk flow of helium through the side arm of the T-connector. As the flow rate of the vacuum just exceeds that of the helium inflow, the dense gold microparticles continue along their initial trajectory through the T- and hypodermic needle connectors to the gel loading pipette tip for emission. During this process, the ethanol is removed and/or evaporates such that the microparticles are dried by the time they reach the target retinal tissue after a brief flight through air.