Engineers have discovered a simple and inexpensive means of directing lipid nanoparticles (LNPs), the revolutionary molecules that delivered the COVID-19 vaccines, to target specific tissues, presaging a new era in personalized medicine and gene therapy. The key is making small changes to the chemical structure of LNPs, including the incorporation of siloxane, a chemical group that includes silicon, whose wider atomic radius increases membrane flexibility and improves mRNA uptake by target cells.