Aggregation effects for thermoplasmonics and MRI with hybrid nanoparticles

This study evaluates a combined approach for magnetic resonance imaging (MRI) and photothermal therapy using hybrid gold-magnetite nanoshell clusters. The clusters convert laser light into heat and change the transverse relaxation rate (R₂), providing MRI contrast. We determine whether MRI can track the temperature rise during continuous illumination when nanoparticles aggregate. Finite-element simulations quantify heat generation for single clusters, and an overall heat-transfer model predicts the temperature increase in a solution containing many clusters. An analytical relaxation model is used to compute R₂ while accounting for aggregation and temperature. We find an optimal cluster size and particle volume fraction that maximize local heating. At the solution scale, aggregation usually reduces the temperature rise and weakens the R₂ change, lowering MRI sensitivity. Nevertheless, the R₂ difference between dispersed and strongly aggregated states remains well defined, suggesting that MRI could help monitor laser-induced changes in nanoparticle spatial organization during photothermal therapy.