The extraordinary small size of NPs makes them difficult to detect and quantify once distributed in a material or biological system. We present a simple and straightforward method for the direct proton beam activation of synthetic or commercially available aluminum oxide NPs (Al2O3 NPs) via the 16O(p,α)13N nuclear reaction in order to assess their biological fate using positron emission tomography (PET). The radiolabeling of the NPs does not alter their surface or structural properties as demonstrated by TEM, DLS, and ζ-potential measurements. The incorporation of radioactive 13N atoms in the Al2O3 NPs allowed the study of the biodistribution of the metal oxide NPs in rats after intravenous administration via PET. Despite the short half-life of 13N (9.97 min), the accumulation of NPs in different organs could be measured during the first 68 min after administration. The percentage amount of radioactivity per organ was calculated to evaluate the relative amount of NPs per organ. This simple and robust activation strategy can be applied to any synthetic or commercially available metal oxide particle.

The synthesis of (18)F-labelled positron emitting NPs by direct irradiation of (18)O-enriched aluminum oxide NPs with 16 MeV protons is reported. Biodistribution studies of the labelled particles after intravenous administration were performed in male rats using positron emission tomography. The simple and general activation strategy can be applied to any in situ prepared core metal oxide particle for direct use or subsequent bio-compatible coating or encapsulation followed by functionalization.

The determination of nanoparticle (NP) stability and degradation in vivo is essential for the accurate evaluation of NP biodistribution in medical applications and for understanding their toxicological effects. Such determination is particularly challenging because NPs are extremely difficult to detect and quantify once distributed in a biological system. Radiolabelling with positron or gamma emitters and subsequent imaging studies using positron emission tomography (PET) or single-photon emission computerised tomography (SPECT) are some of the few valid alternatives. However, NPs that degrade or radionuclides that detach or are released from the NPs can cause artefact. Here, submicron-sized poly(lactide-coglycolide) nanoparticles (PLGA-NPs) stabilised with bovine serum albumin (BSA) were dual radiolabelled using gamma emitters with different energy spectra incorporated into the core and coating. To label the core, 111 In-doped iron oxide NPs were encapsulated inside PLGA-NPs during NP preparation, and the BSA coating was labelled by electrophilic substitution using 125 I. After intravenous administration into rats, energy-discriminant SPECT resolved each radioisotope independently. Imaging revealed different fates for the core and coating, with a fraction of the two radionuclides co-localising in the liver and lungs for long periods of time after administration, suggesting that NPs are stable in these organs. Organ harvesting followed by gamma counting corroborated the SPECT results. The general methodology reported here represents an excellent alternative for visualising the degradation process of multi-labelled NPs in vivo and can be extended to a wide range of engineered NPs. 20009,

A simple and straightforward method is presented for the direct proton beam activation of 18O‐enriched titanium dioxide nanoparticles (TiO2 NPs) via the 18O(p,n)18F nuclear reaction in order to assess the biological fate of the NPs using positron emission tomography (PET). The radiolabeling of the NPs does not alter their morphological properties as demonstrated by transmission electron microscopy and dynamic light scattering measurements. The simultaneous formation of other radioisotopes by activation of the titanium atom, i.e., 48V, 47V, 44gSc, has been investigated using high‐resolution gamma spectrometry and PET. The labeling of TiO2 NPs with radioactive 18F atoms makes it possible to perform short‐term in vivo biodistribution studies of the metal oxide NPs in rats after intravenous and oral administration using PET. The accumulation of NPs in different organs could be quantified during almost 8 h after administration.