A rational study of the influence of Mn²⁺-insertion in Prussian blue nanoparticles on their photothermal properties

We investigated a series of Mn2+-Prussian blue (PB) nanoparticles NazMnxFe1-x[Fe(CN)6]1-y□y·nH2O of similar size, surface state and cubic morphology with various amounts of Mn2+ synthesized through a one step self-assembly reaction. We demonstrated by a combined experimental-theoretical approach that during the synthesis, Mn2+ substituted Fe3+ up to a Mn/Na-Mn-Fe ratio of 32 at% in the PB structure, while for higher amounts, the Mn2[Fe(CN)6] analogue is obtained. For comparison, the post-synthetic insertion of Mn2+ in PB nanoparticles was also investigated and completed with Monte-Carlo simulations to probe the plausible adsorption sites. The photothermal conversion efficiency (η) of selected samples was determined and showed a clear dependence on the Mn2+amount with a maximum efficiency for a Mn/Na-Mn-Fe ratio of 10 at% associated with a dependence on the nanoparticle concentration. Evaluation of the in vitro photothermal properties of these nanoparticles performed on triple negative human breast adenocarcinoma (MDA-MB-231) cells by using continuous and pulsed laser irradiation confirm their excellent PTT efficiency permitting low dose use.