particles, whilemicrocarrierwas the term originally designated for the particles, as they are
small and carry the DNA). The controlled explosion used to accelerate the macrocarrier is
provided by high-pressure helium, which is released from a small chamber following the
breakage of a ruptured disk, designed to break at specific pressures. The macrocarrier,
with the particles on one side, travels a short distance and smashes into a screen, stopping
the macrocarrier and allowing the particles to continue along their path. In most cases, the
whole procedure is performed under partial vacuum, because the presence of air slows
down the particles. A partial vacuum, applied for a short duration, does not appear to
damage the biological targets.
Although there are numerous versions of particle bombardment devices (Fig. 10.7),
they all utilize the same basic approach and are similarly patent-protected. The main man-
ufacturer of particle bombardment devices is Bio-Rad, who offers two different versions of
the device. While one version is a large, heavy, vacuum-utilizing, research lab unit, the
other version is handheld and moderately portable. The handheld Helios device has
received more attention for gene therapy work, while the large, benchtop unit is standard
in most plant transformation laboratories. There is certainly a cost associated with all of
these devices, which limits the use of particle bombardment for those academic research
laboratories with insufficient resources.
10.4.2 The Fate of Introduced DNA
For DNA introduction using particle bombardment, DNA is first precipitated onto the par-
ticles using either calcium chloride or ethanol, which are commonly used for DNA precipi-
tation. When the DNA precipitates, it sticks to whatever is at hand. It is unclear how
“tightly” the DNA is bound to the particles, but it must be able to withstand the incredible
force of acceleration and cell wall/cytoplasm penetration and also come off the particles
after delivery.
Figure 10.7.Two different particle bombardment devices: (a) the commercially available PDS-
1000 /He (Bio-Rad) and (b) the noncommercial particle inflow gun (right).
10.4. PARTICLE BOMBARDMENT 257