Abstract:Many of the solution phase properties of nanoparticles, such as their colloidal stability and hydrodynamic diameter, are governed by the number of stabilizing groups bound to the particle surface (i.e., grafting density). Here we show how two techniques, analytical ultracentrifugation (AUC) and total organic carbon analysis (TOC), can be applied separately to the measurement of this parameter. AUC directly measures the density of nanoparticle–polymer conjugates while TOC provides the total carbon content of it… Show more
“…To calculate the grafting density of PEG on SPION, we assume that SPION is spherical in shape with a radius of 5.5 nm with a surrounding PEG layer (MW PEG = 3350 gm/mol). Using the following equation [47]:where ρ
SPION and N A are the density of SPION (5.24 g/cm 3 ) and Avogadro’s number, respectively, and introducing the respective values we obtained a grafting density of ~5 chains/nm 2 . This relatively high value implies that the PEG chain is densely packed on SPION core, as expected, and responsible for the steric repulsion in the solution.Fig.…”
Superparamagnetic iron oxide nanoparticles (SPIONs, ~11-nm cores) were PEGylated without anchoring groups and studied as efficient MRI T
2 contrast agents (CAs). The ether group of PEG is efficiently and directly linked to the positively charged surface of SPIONs, and mediated through a dipole-cation covalent interaction. Anchor-free PEG-SPIONs exhibit a spin-spin relaxivity of 123 ± 6 mM−1s−1, which is higher than those of PEG-SPIONs anchored with intermediate biomolecules, iron oxide nanoworms, or Feridex. They do not induce a toxic response for Fe concentrations below 2.5 mM, as tested on four different cell lines with and without an external magnetic field. Magnetic resonance phantom imaging studies show that anchor-free PEG-SPIONs produce a significant contrast in the range of 0.1–0.4 [Fe] mM. Our findings reveal that the PEG molecules attached to the cores immobilize water molecules in large regions of ~85 nm, which would lead to blood half-life of a few tens of minutes. This piece of research represents a step forward in the development of next-generation CAs for nascent-stage cancer detection.Graphical AbstractContrast-probed anchor-free PEGylated iron oxide contrast agent
Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-017-2084-y) contains supplementary material, which is available to authorized users.
“…To calculate the grafting density of PEG on SPION, we assume that SPION is spherical in shape with a radius of 5.5 nm with a surrounding PEG layer (MW PEG = 3350 gm/mol). Using the following equation [47]:where ρ
SPION and N A are the density of SPION (5.24 g/cm 3 ) and Avogadro’s number, respectively, and introducing the respective values we obtained a grafting density of ~5 chains/nm 2 . This relatively high value implies that the PEG chain is densely packed on SPION core, as expected, and responsible for the steric repulsion in the solution.Fig.…”
Superparamagnetic iron oxide nanoparticles (SPIONs, ~11-nm cores) were PEGylated without anchoring groups and studied as efficient MRI T
2 contrast agents (CAs). The ether group of PEG is efficiently and directly linked to the positively charged surface of SPIONs, and mediated through a dipole-cation covalent interaction. Anchor-free PEG-SPIONs exhibit a spin-spin relaxivity of 123 ± 6 mM−1s−1, which is higher than those of PEG-SPIONs anchored with intermediate biomolecules, iron oxide nanoworms, or Feridex. They do not induce a toxic response for Fe concentrations below 2.5 mM, as tested on four different cell lines with and without an external magnetic field. Magnetic resonance phantom imaging studies show that anchor-free PEG-SPIONs produce a significant contrast in the range of 0.1–0.4 [Fe] mM. Our findings reveal that the PEG molecules attached to the cores immobilize water molecules in large regions of ~85 nm, which would lead to blood half-life of a few tens of minutes. This piece of research represents a step forward in the development of next-generation CAs for nascent-stage cancer detection.Graphical AbstractContrast-probed anchor-free PEGylated iron oxide contrast agent
Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-017-2084-y) contains supplementary material, which is available to authorized users.
“…TGA results suggested that ZnO-OA and ZnO-PSAN nanoparticles were comprised of 81% and 70% wt inorganic material, respectively. Through knowledge of the size, density, molecular weight, and relative mass contribution of core/ligand materials, grafting densities (σ) [16], that is, the ligand-loadings on the surface of the nanoparticles, were calculated. Using these results, σ trad values were determined to be 5.3 and 0.9 nm -2 for ZnO-OA and ZnO-PSAN nanoparticles, respectively [14].…”
Zinc oxide (ZnO) nanoparticles coated with either n-octylamine (OA) or α-amino poly(styrene-co-acrylonitrile) (PSAN) ligands (L) have been analyzed using laser desorption/ionization and matrix assisted laser desorption/ionization (MALDI) time-of-flight (TOF) superconducting tunnel junction (STJ) cryodetection mass spectrometry. STJ cryodetection has the advantage of high m/z detection and allows for the determination of average molecular weights and dispersities for 500-600 kDa ZnO-L nanoparticles. The ability to detect the relative energies deposited into the STJs has allowed for investigation of ZnO-L metastable fragmentation. ZnO-L precursor ions gain enough internal energy during the MALDI process to undergo metastable fragmentation in the flight tube. These fragments produced a lower energy peak, which was assigned as ligand-stripped ZnO cores whereas the individual ligands were at too low of an energy to be observed. From these STJ energy resolved peaks, the average weight percentage of inorganic material making up the nanoparticle was determined, where ZnO-OA and ZnO-PSAN nanoparticles are comprised of ~62% and ~68% wt ZnO, respectively. In one example, grafting densities were calculated based on the metastable fragmentation of ligands from the core to be 16 and 1.1 nm for ZnO-OA and ZnO-PSAN, respectively, and compared with values determined by thermogravimetric analysis (TGA) and transmission electron microscopy (TEM). Graphical Abstract ᅟ.
“…BT-PEI samples were prepared as above, and centrifuged at 17000 rcf for 10 minutes to sediment particles and washed with 1 mL PB and centrifuged again for 5 minutes. The particles were added to alumina pans and run on the TGA, first heating at 100 °C for 1h and then ramped up to 500 °C at a rate of 2 °C/min [16]. …”
Barium titanate nanoparticles (BT NP) belong to a class of second harmonic generating (SHG) nanoprobes that have recently demonstrated promise in biological imaging. Unfortunately, BT NPs display low cellular uptake efficiencies, which may be a problem if cellular internalization is desired or required for a particular application. To overcome this issue, while concomitantly developing a particle platform that can also deliver nucleic acids into cells, we coated the BT NPs with the cationic polymer polyethylenimine (PEI) – one of the most effective nonviral gene delivery agents. Coating of BT with PEI yielded complexes with positive zeta potentials and resulted in an 8-fold increase in cellular uptake of the BT NPs. Importantly, we were able to achieve high levels of gene delivery with the BT-PEI/DNA complexes, supporting further efforts to generate BT platforms for coupled imaging and gene therapy.
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