For transformation, micro-particles coated with DNA to be bombarded from gene gun are made up of

The gene gun technique, also known as biolistic particle delivery, biolistics, or particle bombardment, was developed in the early 1980s. This technique has revolutionized the science of genetic engineering, which involves manipulating an organism's genes. Gene gun technology involves delivering DNA or RNA coated on microscopic gold or titanium particles (bullets) into living tissues. The high-velocity acceleration of particles using the gene gun may be provided by compressed gas, centripetal force (external force to move a body along a curved path), electric discharge, or firing explosives. Acceleration provides the necessary force to puncture the cell membrane and deliver the materials into the cells of living tissues.