Biocompatible-nanoparticle-emulsion (BCNE) containing poly(ethylene glycol) (PEG) diacrylate hydrogel nanoparticles, synthesized through inverse miniemulsion polymerization, suspended in oil provides number of advantages over standard PEG-coated particles and lipoplexes. One is sustained delivery with single dosage. The 3-dimensional-crosslinked-mesh nature of our particle -rather than a coating- allows for therapeutic entrapment and sustained release upon particle swelling in aqueous environments. Beyond this, the mesh size can be controllably tuned, allowing for loading different-sized molecules: we have successfully loaded and delivered polyphosphates, peptides, siRNAs, and mRNAs. Another advantage is the elimination of emulsion post-processing, achievable through an oil phase substitution, resulting in stable particles, increased yield, and decreased particle aggregation. This use of soybean oil over cyclohexane -toxic organic- also increases in vivo biocompatibility. The biocompatibility of the nanoparticles and emulsion en masse are what allow for successful intracellular delivery of the payload to multiple cell types, including fibroblasts and the challenging-to-transfect mature adipocytes.