Gold carriers (0.8–1.5 µm) were obtained from Alfa Aeser
GmbH & Co KG (Karlsruhe, Germany). Coating with DNA was
performed according to the manufacturer's specifications by
using the Tubing Prep Station (Bio-Rad, München, Germany)
and the pcDNA3.1/V5-His-TOPO constructs. The amount of
expression plasmid per 75 cm length of gold-coated tubing was
set to 35 µg. After the coating procedure the tubing was cut into
cartridges of 1.25 cm in length and stored at 4 °C in a desiccator.