Assembly and Stability of Lipid-Coated Silver Nanoparticles: A Combined UV-VIS / Multispectral iSCAT Study

Although silver nanoparticles (AgNPs) have superb optical properties, insufficient chemical stability and inertness precludes their application in many biosensing applications. Lipid-coating is a potential strategy to enhance the stability of AgNPs in complex chemical environments, but the lipid assembly depends on several parameters that require optimization. Stability assays are key for performance optimization, but conventional ensemble-based strategies may obscure an underlying heterogeneity of these hybrid nanostructures. In this work, we employ multispectral interferometric scattering (iSCAT) microscopy to characterize the oxidative etching of lipid-coated silver NPs (L-AgNPs) at the single-particle level. By monitoring the real-time etching of individual NPs, we resolve a distinct bimodal behavior that is undetectable via bulk UV-Vis spectroscopy: particles either undergo rapid etching or remain kinetically inert, indicating that the protection provided by the membrane in this assay is an "all-or-nothing" phenomenon. The probability of achieving AgNP stabilization is dependent on the temperature during the assembly. We demonstrate that maintaining the lipid formulation in the fluid phase during both liposome precursor formation and L-AgNP self-assembly optimizes the yield of stable, protected L-AgNPs. These findings also highlight the power of single-particle interferometric imaging for characterizing the structural integrity of hybrid nanomaterials and optimizing assembly conditions.