Analytical techniques for characterisation - WIP Flashcards
of nanoparticles
What does chemical characterisation include?
Chemical composition
Surface composition and density
Structural properties
Mass concentration
What are some examples of physical properties? *
Mean size, size distribution
Shape and morphology
Surface charge (zeta potential is a proxy) - if there is no surface charge they are likely to collapse into other nanoparticles (aggregate)
Physical stability – constant properties? Aggregation? Change in morphology?
What are some examples of chemical characterisation techniques?
XDR (x-ray diffraction) - crystalline structure of nanoparticles
XPS (x-ray photoelectron spectroscopy) - element and surface composition
SEM-EDX – elemental and surface composition
NMR – chemical and surface composition
FTIR – surface composition
Raman spec – surface composition
ICP-OES (inductively coupled plasma – optical emission spectroscopy) or ICP-MS - elemental composition, mass concentration
HPLC – chemical composition
UV-vis spectroscopy – optical properties, nanoparticle concentration
What is TEM?
(transmission electron microscopy)
< 0.5nm resolution, 4 million times better than naked eye
Electron source in vacuum for imaging, focused using electromagnetic lenses into sample, CCD camera, can digitally convert image
Sample is made of materials, some of which can absorb electrons, some cannot
Sample prep – sample solution pipetted onto carbon coated grid, dried and loaded under vacuum conditions. carbon membrane on grid can absorb sample, and doesn’t absorb electrons.
Negative staining – sample embedded by a dried amorphous layer of heavy metal-containing cationic or anionic salt. Provides contrast for example when the nanoparticles do not absorb electrons enough
Cryo-EM – sample cooled to cryogenic temperatures (do not add any contrast, so requires very powerful microscopes compared to negative staining) and embedded into an environment of vitreous water. No drying preserves the structure. Mostly used for structural biology (direct imaging of macromolecules)
Pros – near atomic resolution, direct and accurate measurement nanoparticle size distribution, provides information about shape/morphology of nanoparticles
Cons – sample processing may alter nanoparticles or generate artifacts, dried samples are far from native conditions, time consuming, expensive to run/buy and may have a massive footprint
What is ATM? *
(atomic force microscopy)
What is DLS?
(dynamic light scattering) laser scattering technique
Determining size distribution of nanoparticles using Brownian motion
Diffusion coefficient is directly proportional to the temperature
If a particle is non-spherical it still moves with the same Brownian motion
Pros – fast routine method, benchtop instrument, accessible cost, almost no training needed, nanoparticles are in solution in their native environment, direct and accurate measurement of nanoparticle size distribution
Cons – no information about shape/morphology of nanoparticles, the hydrodynamic diameter is larger than the solid diameter (?), the scattering intensity is proportional to the 6th power of the size:aggregates (large debris affect the accuracy), unsuitable for polydisperse particles
What is NTA? *
(nanoparticle tracking analysis) laser scattering technique
Pros – opposite to DLS (can deal with polydisperse particles), benchtop instrument, accessible cost, direct and accurate measurement of nanoparticle size distribution
Cons – more time consuming than DLS, particle concentration must be within a precise window (sample dilution may alter the properties), no information about shape/morphology, the hydrodynamic diameter is larger than the solid diameter (?*), large debris may prevent analysis
What is ELS? *
(electrophoretic light scattering) laser scattering technique
doppler effect? *
