343 research outputs found
Gel Electrophoresis of Gold-DNA Nanoconjugates
Gold-DNA conjugates were investigated in detail by a comprehensive gel electrophoresis study based on 1200 gels. A controlled number of single-stranded DNA of different length was attached specifically via thiol-Au bonds to phosphine-stabilized colloidal gold nanoparticles. Alternatively, the surface of the gold particles was saturated with single stranded DNA of different length either specifically via thiol-Au bonds or by nonspecific adsorption. From the experimentally determined electrophoretic mobilities, estimates for the effective diameters of the gold-DNA conjugates were derived by applying two different data treatment approaches. The first method is based on making a calibration curve for the relation between effective diameters and mobilities with gold nanoparticles of known diameter. The second method is based on Ferguson analysis which uses gold nanoparticles of known diameter as reference database. Our study shows that effective diameters derived from gel electrophoresis measurements are affected with a high error bar as the determined values strongly depend on the method of evaluation, though relative changes in size upon binding of molecules can be detected with high precision. Furthermore, in this study, the specific attachment of DNA via gold-thiol bonds to Au nanoparticles is compared to nonspecific adsorption of DNA. Also, the maximum number of DNA molecules that can be bound per particle was determined
Evidence of coexistence of change of caged dynamics at Tg and the dynamic transition at Td in solvated proteins
Mossbauer spectroscopy and neutron scattering measurements on proteins
embedded in solvents including water and aqueous mixtures have emphasized the
observation of the distinctive temperature dependence of the atomic mean square
displacements, , commonly referred to as the dynamic transition at some
temperature Td. At low temperatures, increases slowly, but it assume
stronger temperature dependence after crossing Td, which depends on the
time/frequency resolution of the spectrometer. Various authors have made
connection of the dynamics of solvated proteins including the dynamic
transition to that of glass-forming substances. Notwithstanding, no connection
is made to the similar change of temperature dependence of obtained by
quasielastic neutron scattering when crossing the glass transition temperature
Tg, generally observed in inorganic, organic and polymeric glass-formers.
Evidences are presented to show that such change of the temperature dependence
of from neutron scattering at Tg is present in hydrated or solvated
proteins, as well as in the solvents used unsurprisingly since the latter is
just another organic glass-formers. The obtained by neutron scattering at
not so low temperatures has contributions from the dissipation of molecules
while caged by the anharmonic intermolecular potential at times before
dissolution of cages by the onset of the Johari-Goldstein beta-relaxation. The
universal change of at Tg of glass-formers had been rationalized by
sensitivity to change in volume and entropy of the beta-relaxation, which is
passed onto the dissipation of the caged molecules and its contribution to
. The same rationalization applies to hydrated and solvated proteins for
the observed change of at Tg.Comment: 28 pages, 10 figures, 1 Tabl
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Temperature dependence of protein dynamics simulated with three different water models
The effect of variation of the water model on the temperature dependence of protein and hydration water dynamics is examined by performing molecular dynamics simulations of myoglobin with the TIP3P, TIP4P, and TIP5P water models and the CHARMM protein force field at temperatures between 20 and 300 K. The atomic mean-square displacements, solvent reorientational relaxation times, pair angular correlations between surface water molecules, and time-averaged structures of the protein are all found to be similar, and the protein dynamical transition is described almost indistinguishably for the three water potentials. The results provide evidence that for some purposes changing the water model in protein simulations without a loss of accuracy may be possible
Electrical transport through self-assembled colloidal nanomaterials and their perspectives
Colloidal nanoparticles developed as interesting objects to establish two- or
three-dimensional super-structures with properties not known from conventional
bulk materials. Beyond, the properties can be tuned and quantum effects can be
exploited. This allows understanding electronic and optoelectronic transport
phenomena and developing corresponding devices. The state-of-the-art in this
field will be reviewed and possible challenges and prospects will be
identified.Comment: 8 pages. arXiv admin note: text overlap with arXiv:1501.0236
Surface Science of DNA Adsorption onto Citrate-Capped Gold Nanoparticles
This document is the Accepted Manuscript version of a Published Work that appeared in final form in Langmuir copyright © American Chemical Society after peer review and technical editing by publisher. To access the final edited and published work see Zhang, X., Servos, M. R., & Liu, J. (2012). Surface Science of DNA Adsorption onto Citrate-Capped Gold Nanoparticles. Langmuir, 28(8), 3896–3902. https://doi.org/10.1021/la205036pSingle-stranded DNA can be adsorbed by citrate capped gold nanoparticles (AuNPs), resulting in increased AuNP stability, which forms the basis of a number of biochemical and analytical applications, but the fundamental interaction of this adsorption reaction remains unclear. In this study, we measured DNA adsorption kinetics, capacity, and isotherms, demonstrating that the adsorption process is governed by electrostatic forces. The charge repulsion among DNA strands and between DNA and AuNPs can be reduced by adding salt, reducing pH or by using noncharged peptide nucleic acid (PNA). Langmuir adsorption isotherms are obtained, indicating the presence of both adsorption and desorption of DNA from AuNPs. While increasing salt concentration facilitates DNA adsorption, the desorption rate is also enhanced in higher salt due to DNA compaction. DNA adsorption capacity is determined by DNA oligomer length, DNA concentration, and salt. Previous studies indicated faster adsorption of short DNA oligomers by AuNPs, we find that once adsorbed, longer DNAs are much more effective in protecting AuNPs from aggregation. DNA adsorption is also facilitated by using low pH buffers and high alcohol concentrations. A model based on electrostatic repulsion on AuNPs is proposed to rationalize the DNA adsorption/desorption behavior.University of Waterloo ||
Canadian Foundation for Innovation ||
Ontario Ministry of Research & Innovation ||
Canadian Institutes of Health Research ||
Natural Sciences and Engineering Research Council |
Quantum Dots Do Not Affect the Behaviour of Mouse Embryonic Stem Cells and Kidney Stem Cells and Are Suitable for Short-Term Tracking
Quantum dots (QDs) are small nanocrystals widely used for labelling cells in order to enable cell tracking in complex environments in vitro, ex vivo and in vivo. They present many advantages over traditional fluorescent markers as they are resistant to photobleaching and have narrow emission spectra. Although QDs have been used effectively in cell tracking applications, their suitability has been questioned by reports showing they can affect stem cell behaviour and can be transferred to neighbouring cells. Using a variety of cellular and molecular biology techniques, we have investigated the effect of QDs on the proliferation and differentiation potential of two stem cell types: mouse embryonic stem cells and tissue-specific stem cells derived from mouse kidney. We have also tested if QDs released from living or dead cells can be taken up by neighbouring cells, and we have determined if QDs affect the degree of cell-cell fusion; this information is critical in order to assess the suitability of QDs for stem cell tracking. We show here that QDs have no effect on the viability, proliferation or differentiation potential of the two stem cell types. Furthermore, we show that the extent of transfer of QDs to neighbouring cells is <4%, and that QDs do not increase the degree of cell-cell fusion. However, although the QDs have a high labelling efficiency (>85%), they are rapidly depleted from both stem cell populations. Taken together, our results suggest that QDs are effective cell labelling probes that are suitable for short-term stem cell tracking
Capillary electrophoretic separation of nanoparticles
In the present work, CdSe nanocrystals (NCs) synthesized with a trioctylphosphine surface passivation layer were modified using amphiphilic molecules to form a surface bilayer capable of providing stable NCs aqueous solutions. Such modified nanocrystals were used as a test solute in order to analyze new electrophoretic phenomena, by applying a micellar plug as a separation tool for discriminating nanocrystals between micellar and micelle-free zones during electrophoresis. The distribution of NCs between both zones depended on the affinity of nanocrystals towards the micellar zone, and this relies on the kind of surface ligands attached to the NCs, as well as electrophoretic conditions applied. In this case, the NCs that migrated within a micellar zone can be focused using a preconcentration mechanism. By modifying electrophoretic conditions, NCs were forced to migrate outside the micellar zone in the form of a typical CZE peak. In this situation, a two-order difference in separation efficiencies, in terms of theoretical plates, was observed between focused NCs (N ~ 107) and a typical CZE peak for NCs (N ~ 105). By applying the amino-functionalized NCs the preconcentration of NCs, using a micellar plug, was examined, with the conclusion that preconcentration efficiency, in terms of the enhancement factor for peak height (SEFheight) can be, at least 20. The distribution effect was applied to separate CdSe/ZnS NCs encapsulated in silica, as well as surface-modified with DNA, which allows the estimation of the yield of conjugation of biologically active molecules to a particle surface
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