Degradation of magnetic nanoparticles mimicking lysosomal conditions followed by AC susceptibility

[Background] A deeper knowledge on the effects of the degradation of magnetic nanoparticles on their magnetic properties is required to develop tools for the identification and quantification of magnetic nanoparticles in biological media by magnetic means.[Methods] Citric acid and phosphonoacetic acid-coated magnetic nanoparticles have been degraded in a medium that mimics lysosomal conditions. Magnetic measurements and transmission electron microscopy have been used to follow up the degradation process.[Results] Particle size is reduced significantly in 24 h at pH 4.5 and body temperature. These transformations affect the magnetic properties of the compounds. A reduction of the interparticle interactions is observed just 4 h after the beginning of the degradation process. A strong paramagnetic contribution coming from the degradation products appears with time.[Conclusions] A model for the in vivo degradation of magnetic nanoparticles has been followed to gain insight on the changes of the magnetic properties of iron oxides during their degradation. The degradation kinetics is affected by the particle coating, in our case being the phosphonoacetic acid-coated particles degraded faster than the citric acid-coated ones.LG is the beneficiary of a postdoctoral grant from the AXA Research Fund and GBdS, of a sandwich-PhD grant from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq – Brazil). This work was also supported by the 7th framework programme of the European Commission Directorate-General for Research and Innovation (Nanomag 604448). X-ray diffraction, FTIR spectroscopy, and thermogravimetric and chemical analysis were carried out in the support laboratories of Instituto de Ciencia de Materiales de Madrid (CSIC).Peer reviewe