You could try looking at the following publication (PMID: 21663596). They used a similar technique (spermidine/CaCl2) as is used to coat gold microcarriers with DNA.
BMC Biotechnol. 2011 Jun 10;11:66. doi: 10.1186/1472-6750-11-66.
Nano-biolistics: a method of biolistic transfection of cells and tissues using a gene gun with novel nanometer-sized projectiles.