Heterogeneous Reactivity of Palladium Nanoparticles Revealed by Wavelength-Resolved Interferometric Scattering

Pd nanoparticles are used in a variety of applications, and thus techniques that enable their high-throughput, label-free detection, as well as in situ reaction monitoring at catalytically relevant sizes, are needed to establish robust structure-function relationships. Here, we introduce wavelength-resolved interferometric scattering (iSCAT) as a strategy for performing these studies, over a range of Pd nanoparticle sizes. From a sample of ∼90 nm Pd octahedra we spectroscopically discriminate structural outliers based on their scattering resonances and spectral lineshapes, using simulations to validate the structure-spectral relationships. We then demonstrate direct detection of single Pd nanocubes with <20 nm edge length and track changes occurring to them in different reactive conditions, uncovering both interparticle heterogeneity and wavelength-dependent photochemistry. The results highlight the power of wavelength-resolved iSCAT for studying Pd nanoparticle transformations in situ and offer new insights into Pd reactivity at the nanoscale.