From transmission electron microscopy (TEM) images (Figure 3) match the grain sizes predicted by XRD, indicating that the core particles were a single crystal phase. Neutron activation analysis of magnetically separated La0.5Gd0.5PO4 core NPs gives a La toFigure 4. TEM of a characteristic cluster of NPs. EELS analysis indicates the presence of La, Gd, and Au in all particles in the cluster. doi:10.1371/journal.pone.0054531.gGd mole ratio of 1.1160.03. Pure LaPO4 and pure GdPO4 exhibited larger grain sizes than their mixed counterparts. Addition of GdPO4 shells to 11967625 the core La0.5Gd0.5PO4 NP causes epitaxial growth of the particle. Mean diameters increase sequentially with each shell addition (Table 1). Addition of four GdPO4 shells to the core La0.5Gd0.5PO4 produces 22 nm diameter NPs and addition of an outer gold layer increases the particle diameter to 27 nm. Electron energy loss spectroscopy (EELS)-TEM images of the NPs are shown in Figure 4. Gold coated NPs with four epitaxially added GdPO4 shells were further characterized by dynamic light scattering. Hydrodynamic diameters and zeta potentials are shown in Table 2. An increase of the hydrodynamic diameter on addition of polyethylene glycol (PEG) and antibody is common for NPs. The highly negative zeta potentials should lead to stability in water which was confirmed by monitoring changes in the UV-Vis spectrum of the particles over a 1 month period in both 18 MV water and saline solution. No shift was observed in the plasmon resonance over this time period. Nanoparticles with GdPO4 shells followed by Au coating dramatically increased radioactive daughter retention in vitro compared with previously published results for core-only lanthanum phosphate NPs [28]. Adding 2 shells increased retention of the 221Fr daughter from 50 for the LaPO4 core to 70 . With four shells of GdPO4, the initial retention of the 221Fr daughter was 98 . Daughter retention decreased by roughly 2 per day over the course of a week, and stabilized at 88 . Further, the presence of the Au/4 GdPO4 shells increased the retention of the 225 Ac parent itself by roughly an order of magnitude. Over the course of 3 weeks, the multi-layered particles retained greater than 99.99 of the 225Ac parent radionuclide. Particles with more than 4 shells of GdPO4 settled out of solution rapidly and were difficult to manipulate. Monitoring the plasmon resonance indicated that the multi-layered particles remained stable towards aggregation in PBS over the course of one month. For in vivo biodistribution testing, the NPs were conjugated to the mAb 201b monoclonal antibody via a lipoic acid-PEG12COOH linker [29]. MAb 201b targets thrombomodulin receptors which are highly expressed in lung endothelium. The antibody quickly localizes to its vascular target and clears from circulation with a half-life of 40 hours [30]. 3-sulfo-N-hydroxysuccinimide (sulfo-NHS) and 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) activated the carboxylate of the PEG for coupling to amine Title Title Loaded From File Loaded From File groups on the antibody, leading to the formation of an amide bond. The reaction was quenched with glycine and conjugates were purified by centrifugation. The conjugated NPs were redispersed in phosphate buffered saline (PBS) containing bovine serum albumin (BSA). The antibody conjugation process is summarized in Figure 5.Gold Coated LnPO4 Nanoparticles for a RadiotherapyTable 2. Dynamic light scattering of NPs in 18 MV water.Particle La0.5Gd0.5(Hydrodynamic dia.From transmission electron microscopy (TEM) images (Figure 3) match the grain sizes predicted by XRD, indicating that the core particles were a single crystal phase. Neutron activation analysis of magnetically separated La0.5Gd0.5PO4 core NPs gives a La toFigure 4. TEM of a characteristic cluster of NPs. EELS analysis indicates the presence of La, Gd, and Au in all particles in the cluster. doi:10.1371/journal.pone.0054531.gGd mole ratio of 1.1160.03. Pure LaPO4 and pure GdPO4 exhibited larger grain sizes than their mixed counterparts. Addition of GdPO4 shells to 11967625 the core La0.5Gd0.5PO4 NP causes epitaxial growth of the particle. Mean diameters increase sequentially with each shell addition (Table 1). Addition of four GdPO4 shells to the core La0.5Gd0.5PO4 produces 22 nm diameter NPs and addition of an outer gold layer increases the particle diameter to 27 nm. Electron energy loss spectroscopy (EELS)-TEM images of the NPs are shown in Figure 4. Gold coated NPs with four epitaxially added GdPO4 shells were further characterized by dynamic light scattering. Hydrodynamic diameters and zeta potentials are shown in Table 2. An increase of the hydrodynamic diameter on addition of polyethylene glycol (PEG) and antibody is common for NPs. The highly negative zeta potentials should lead to stability in water which was confirmed by monitoring changes in the UV-Vis spectrum of the particles over a 1 month period in both 18 MV water and saline solution. No shift was observed in the plasmon resonance over this time period. Nanoparticles with GdPO4 shells followed by Au coating dramatically increased radioactive daughter retention in vitro compared with previously published results for core-only lanthanum phosphate NPs [28]. Adding 2 shells increased retention of the 221Fr daughter from 50 for the LaPO4 core to 70 . With four shells of GdPO4, the initial retention of the 221Fr daughter was 98 . Daughter retention decreased by roughly 2 per day over the course of a week, and stabilized at 88 . Further, the presence of the Au/4 GdPO4 shells increased the retention of the 225 Ac parent itself by roughly an order of magnitude. Over the course of 3 weeks, the multi-layered particles retained greater than 99.99 of the 225Ac parent radionuclide. Particles with more than 4 shells of GdPO4 settled out of solution rapidly and were difficult to manipulate. Monitoring the plasmon resonance indicated that the multi-layered particles remained stable towards aggregation in PBS over the course of one month. For in vivo biodistribution testing, the NPs were conjugated to the mAb 201b monoclonal antibody via a lipoic acid-PEG12COOH linker [29]. MAb 201b targets thrombomodulin receptors which are highly expressed in lung endothelium. The antibody quickly localizes to its vascular target and clears from circulation with a half-life of 40 hours [30]. 3-sulfo-N-hydroxysuccinimide (sulfo-NHS) and 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) activated the carboxylate of the PEG for coupling to amine groups on the antibody, leading to the formation of an amide bond. The reaction was quenched with glycine and conjugates were purified by centrifugation. The conjugated NPs were redispersed in phosphate buffered saline (PBS) containing bovine serum albumin (BSA). The antibody conjugation process is summarized in Figure 5.Gold Coated LnPO4 Nanoparticles for a RadiotherapyTable 2. Dynamic light scattering of NPs in 18 MV water.Particle La0.5Gd0.5(Hydrodynamic dia.
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