The N/P ratio is crucial in transfection, especially with mRNA and lipid nanoparticles (LNPs). This ratio, representing nitrogen to phosphate, significantly impacts nanoparticle properties such as size and encapsulation efficiency.

What is the N/P Ratio?

The N/P ratio indicates the molar ratio between the amine groups (N) of the ionizable lipid and the phosphate groups (P) of the cargo. For RNA, there's one phosphate group per base, and for DNA, there are two phosphate groups per base. Typical N/P ratios range from three to six, varying with the cargo and ionizable lipid used. Notably, Pfizer and Moderna use a 6:1 N/P ratio in their mRNA vaccine formulations.

How to Calculate the N/P Ratio

Significance of the N/P Ratio

Optimizing the N/P ratio is vital as it influences LNP efficiency. A higher N/P ratio generally results in nanoparticles with more positive charges, enhancing interaction with negatively charged cell membranes, potentially increasing transfection efficiency and affecting cytotoxicity.

Written by

Dr. Marija Petrovic 

Marija is a pharmacist with a PhD in Biopharmacy from the University of Geneva, and a cancer research (ISREC)–trained professional through EPFL, with over seven years of experience in nanomedicine. During her PhD, she worked on miRNA and STING ligand nanocomplexes for cancer immunotherapy, gaining deep expertise in nanoparticle characterization and translational workflows. Certified by the EU-NCL in nanobiotechnology and awarded by Innosuisse (Swiss Innovation Agency) with two prizes (jury and public) for the best life science project, she also earned support from FONGIT, Geneva’s leading deep-tech incubator. As the founder of NanoSphere and an active contributor to the Controlled Release Society (Communication Chair for the Gene Delivery and Editing Group (GDGE), and Industry representative at Nanomedicine and Nanoscale Delivery (NND)), Marija focuses on making next-gen medicine scientific advances more visible, understandable, and useful to the communities that can turn them into impact.