Nanoparticle-Based Photothermal Carriers For Cold-Chain Free Vaccine Delivery: A Pilot Cohort Study

Background: Maintaining vaccines within 2–8 °C during transport remains a critical challenge in low-resource settings where cold-chain failures contribute to potency loss and reduced immunization effectiveness. Nanoparticle-based photothermal carriers integrating photothermal conversion with phase-change buffering may offer a cold-chain-independent solution for stable vaccine delivery. Objective: To evaluate whether nanoparticle-based photothermal carriers improve thermal stability, preserve vaccine potency, and remain operationally feasible during hot-season rural outreach in Pakistan. Methods: A prospective randomized feasibility study compared photothermal carriers incorporating polydopamine–gold nanoparticles with standard ice-pack cold boxes during routine transport of Expanded Programme on Immunization vaccines. Temperature was recorded at 1-minute intervals; potency of returned vials was assessed using validated antigen-specific assays; and community health worker usability was evaluated through structured questionnaires and direct observation. Results: Photothermal carriers maintained temperatures within 2–8 °C for 95.2% of transport time versus 84.7% in standard cold boxes (p<0.001) and eliminated freezing events. Potency retention was significantly higher across all antigens, with gains of 11.7% for measles, 11.2% for rubella, 15.7% for D-antigen, 18.3% for Hib, 7.1% for IPV, and 12.0% for OPV (all p<0.001). Usability scores were higher for photothermal carriers (91 vs 79 for handling; 88 vs 71 for confidence). Conclusion: Nanoparticle-based photothermal carriers substantially enhance thermal stability and vaccine potency, offering a promising cold-chain-independent strategy for improving immunization delivery in resource-limited settings.