Nanoparticles have emerged as powerful vehicles for nucleic acid delivery, enabling breakthroughs in gene therapy, vaccines, and personalized medicine. The ability to safely and efficiently transport siRNA, mRNA, and plasmid DNA into cells has transformed biomedical research and clinical applications. Key nanoparticle platforms include cationic lipids, polymers, and inorganic vectors, each offering distinct advantages for nucleic acid encapsulation, cellular uptake, and intracellular trafficking.

Cationic lipids are among the most widely used non-viral vectors for nucleic acid delivery. These amphiphilic molecules self-assemble into liposomes or lipid nanoparticles (LNPs) through electrostatic interactions with negatively charged nucleic acids. The positively charged headgroups of lipids, such as DOTAP or DODMA, bind to nucleic acids, forming stable complexes that protect the payload from enzymatic degradation. LNPs incorporate helper lipids like cholesterol and PEG-lipids to enhance stability and reduce immunogenicity. A critical feature of lipid-based systems is their ability to facilitate endosomal escape. Ionizable lipids, such as those used in COVID-19 mRNA vaccines, become protonated in the acidic environment of endosomes, disrupting the endosomal membrane and releasing the nucleic acid into the cytoplasm.

Polymeric nanoparticles, particularly those based on polyethylenimine (PEI), offer high nucleic acid loading capacity and tunable physicochemical properties. PEI’s amine-rich structure enables strong electrostatic binding to nucleic acids, forming polyplexes. The proton sponge effect is a key mechanism for endosomal escape, where the buffering capacity of PEI leads to osmotic swelling and endosomal rupture. However, high molecular weight PEI can cause cytotoxicity, prompting the development of degradable or modified variants with reduced toxicity. Other polymers, such as poly(lactic-co-glycolic acid) (PLGA) and chitosan, provide biocompatible alternatives with controlled release profiles.

Inorganic nanoparticles, such as calcium phosphate, present unique advantages for nucleic acid delivery. Calcium phosphate nanoparticles form through co-precipitation with DNA or RNA, resulting in dense, biodegradable complexes. These particles disassemble in the acidic endosomal environment, releasing their cargo. Their biocompatibility and low immunogenicity make them attractive for gene delivery, though challenges in controlling particle size and aggregation persist. Other inorganic vectors, including gold and silica nanoparticles, have been explored for their stability and surface functionalization potential.

Endosomal escape remains a critical barrier for efficient nucleic acid delivery. Nanoparticles must avoid lysosomal degradation by escaping endosomes before enzymatic digestion occurs. Strategies to enhance escape include pH-responsive materials, membrane-disruptive peptides, and fusogenic lipids. Nuclear targeting is another challenge, particularly for plasmid DNA delivery. Nuclear localization signals (NLS) can be incorporated into nanoparticles to facilitate active transport through the nuclear pore complex, though this remains inefficient compared to viral vectors.

The applications of nucleic acid-loaded nanoparticles span gene therapy, vaccines, and genome editing. In gene therapy, siRNA nanoparticles have been developed to silence disease-causing genes, with FDA-approved formulations for hereditary transthyretin-mediated amyloidosis. mRNA-loaded LNPs, exemplified by the Pfizer-BioNTech and Moderna COVID-19 vaccines, demonstrate the potential for rapid vaccine development. These vaccines utilize ionizable lipid nanoparticles to deliver mRNA encoding the SARS-CoV-2 spike protein, eliciting robust immune responses. Plasmid DNA nanoparticles are being explored for CRISPR-Cas9 delivery, enabling precise genome editing for genetic disorders.

Stability and immunogenicity are major considerations in nanoparticle design. Nucleic acids are susceptible to degradation by nucleases, necessitating protective nanoparticle coatings. PEGylation reduces opsonization and extends circulation time, but anti-PEG antibodies can trigger immune responses. Manufacturing challenges include scalability, batch-to-batch variability, and the need for stringent quality control. Cold chain requirements for mRNA-LNP vaccines highlight the importance of improving thermostability.

The success of COVID-19 mRNA vaccines has accelerated interest in nanoparticle platforms for infectious diseases and cancer. Ongoing research focuses on optimizing lipid formulations, enhancing targeting specificity, and reducing reactogenicity. Innovations in microfluidic mixing and continuous manufacturing aim to improve production efficiency.

Nanoparticles for nucleic acid delivery represent a versatile and rapidly advancing field. By addressing challenges in stability, immunogenicity, and intracellular trafficking, these systems hold promise for treating genetic diseases, combating infections, and revolutionizing medicine. The lessons learned from COVID-19 vaccine development will undoubtedly shape the future of nanomedicine.