A method for forming microspheres containing bioactive material, comprising dissolving a polymer matrix, such as albumin or beta-cyclodextrin, in an aqueous medium in a first vessel; contacting the dissolved polymer matrix with a crosslinking agent, such as glutaraldehyde, to crosslink the polymer matrix and the crosslinking agent; neutralizing with sodium bisulfate any excess crosslinking agent remaining after crosslinking is substantially complete; solubilizing in a second vessel a bioactive material in an aqueous solution; mixing the solubilized bioactive material together with the neutralized crosslinked polymer matrix in solution to form a mixture; and, spray drying the mixture to produce nanospheres, whereby substantial bioactivity of the biomaterial is retained upon cellular uptake.