Nanocomposix FAQs

A. We routinely fabricate custom materials for our customers. Please see our custom synthesis page for more information.

A. We routinely functionalize our materials with alternative capping agents or biomolecules for our customers. Please see our custom synthesis page for more information.

A. Our proprietary technologies allow us to fabricate 10’s, 100’s or 1000’s of grams per batch, and to provide significant discounts for large quantity orders. Please contact us for more information.

A. Yes, it is normal for larger gold and silver nanoparticles to settle to the bottom of the storage container. This is completely reversible, simply shake the container for 10-30 seconds until the nanoparticles have redispersed into the solution prior to using the material.

A. Yes, silver will oxidize in the presence of sulfur and oxygen. Please see our Nanotoxicology Knowledge Base for additional details.

A. At the nanoscale it is sometimes cumbersome to use conventional language. We consider them to be polycrystaline, as can be seen by the different lines and contrasts of the particles in TEM images. It is the nature of silver nanoparticles to have the silver atoms reduce into a somewhat regular crystal structure since it is a more stable form–even if it is into many crystal domains in the same particle. By having numerous crystal domains, the particles are able to maintain a near spherical shape. These crystal domains can sometimes be seen as lines in the particles or patches that are darker than the rest of the particle.

A. Unaggregated silver nanoparticles typically have a yellow color in solution and a distinct plasmon resonance. Monitoring the UV-Visible signature of silver nanoparticles over time is a good method of ensuring that the particles are still “good”. If there is a destabilization event, the color will usually change dramatically and it is clear that the particles have aggregated.

A. To spin coat a thin layer you have two choices. One option is to use a much higher concentration of gold nanoparticles. The viscosity won’t increase that much but there will be a larger number of particles in the thin layer of water that will then dry on the surface. Alternatively, the nanoparticles can be transferred to DMSO (cP ~2) which has a higher viscosity and will create a more uniform layer. More info can be found in our Knowledge Base article here.

A. Other methods to create monolayers on a surface include layer by layer (LbL) assembly where nanoparticles with a negative or positive surface charge are exposed to a substrate with the opposite charge. By controlling the incubation time, the concentration of nanoparticles, and the salt level in solutions the density of the applied nanoparticles on the surface can be controlled. More info can be found in our Knowledge Base article here.

A. All of our nanomaterials are provided with specification sheets that include TEM images, particle size statistics and histogram based on 100 individual nanoparticle measurements, UV-Visible extinction spectrum and pH. Hydrodynamic diameter (dynamic light scattering) and zeta potential are also measured for spherical nanoparticles > 10 nm.

A. Mean nanoparticle size is calculated by measuring 100 individual nanoparticles as imaged by TEM. The coefficient of variation is calculated by dividing the standard deviation of the nanoparticle size by the mean nanoparticle size, and multiplying by 100 to get a percentage. For instance, a 50 nm diameter nanosphere with a standard deviation of 3 nm would have a CV of 6% ({3/50}*100=6%).

A. NanoComposix Nanoxact and BioPure nanoparticles are unagglomerated and monodisperse, and each batch of high quality materials is extensively characterized before being shipped to our customers. Some customers have provided us with TEM images where there is a second population of smaller silver nanoparticles visible with TEM analysis. In many of these cases TEM grids with amine, thiol, and carboxy functional were utilized for imaging. The functional groups on these grids can serve as nucleation points for dissolved silver ions resulting in the appearance of small silver nanoparticles that are not present in the colloidal solution. Therefore, we recommend that customers use carbon-coated formvar TEM grids to image silver nanoparticles. More information on this phenomenon can be found in “Generation of Metal Nanoparticles from Silver and Copper Objects”, by R. Glover, et al, ACS 2011

A. Both DLS and zeta potential characterization measure small changes in light scattering as nanomaterials move in solution. Gold and silver nanoparticles with diameters of < 10 nm have very small scattering cross sections, and at dilute concentrations do not scatter enough photons to achieve a signal to noise ratio acceptable for an accurate reading. In some cases, more concentrated solutions can be measured to obtain an acceptable DLS or zeta potential and, in these cases, we do report the values for sizes < 10 nm. Alternatively, centrifugal particle sizing can be used to measure the size distribution of nanoparticles in this size range and we can perform this as a custom service upon request.

A. Some of our gold and silver nanosphere materials require dilution for DLS in order to achieve a reliable measurement. For materials suspended in water or a citrate buffer we will normally dilute with Milli-Q (or DI) water as needed. If the diluted sample is going to be stored or measured after more than a few minutes, we recommend diluting citrate-stabilized materials with a citrate buffer for better stability.Our dilution factor depends on the material:

• 5–20 nm BioPure Gold or Silver (1 mg/mL): measured neat (no dilution)
• 30–40 nm BioPure Gold or Silver (1 mg/mL): dilute 200 uL sample with 800 µL water
• 50–60 nm BioPure Gold or Silver (1 mg/mL): dilute 100 uL sample with 900 µL water
• 70–80 nm BioPure Gold or Silver (1 mg/mL): dilute 50 uL sample with 950 µL water (or similar dilution factor like ~100 µL sample into 2 mL water)
• 90–100 nm BioPure Gold or Silver (1 mg/mL): dilute 20 uL sample with 980 µL water (or similar dilution factor like ~60 µL sample into 3 mL water)

Note: for NanoXact materials (0.05 mg/mL gold or 0.02 mg/mL silver), all sizes should be measured neat with no dilution.

Very small particles like the 20 nm silver or smaller have very low scattering cross sections, so they must be measured at very high concentrations to be able to measure them by DLS. We normally measure these solutions neat (no dilution), but it can still be difficult to obtain reliable results. In all cases, we recommend checking the quality report for their measurement to determine if the results are reliable, and making sure the count rates are within 200–700 kcps for best results.

A. The shape and peak wavelength of the plasmon resonance of silver nanoparticles is influenced by the refractive index of the media it is suspended in. When the particles are in water (n=1.33) the resonance of 80 nm silver nanoparticles is predicted by Mie Scattering theory to be ~462 nm . In air (n=1.0) the peak plasmon resonance of the nanoparticles is predicted to be 398 nm, a shift of 64 nm. In air, if the silver nanoparticle is shelled with a very thick shell of a material that has the same refractive index of water, the peak plasmon wavelength will be close to 462 nm. If the silver is shelled with a very thin shell of material, the peak plasmon resonance will be close to 398 nm. If the shell is of intermediate thickness, the peak will be somewhere between these two extremes (398 nm – 462 nm). Thus, by adjusting the thickness of the shell, the peak resonance of a silica coated silver nanoparticles can be tuned to a particular value.
Since the refractive index of silica is n=1.43, a value greater than water, the silica shell will shift the peak plasmon resonance of a silver nanoparticle suspended in water to a longer wavelength than a silver nanoparticle with no shell. For example, a 50 nm silica shell on an 80 nm silver nanoparticle in water has a predicted peak resonance wavelength of 487 nm, a 25 nm shift compared to an unshelled silver nanoparticle.

This is a common questions due to the unique size and shape dependent optical properties of gold and silver nanoparticles. Please see our Plasmonics webpage for information regarding the optical properties of our standard products, or our Online Mie Theory Simulator for information regarding absorption and scattering splits and silica shelling. Still have questions? Please contact us, and we’d be glad to help you!

Successful imaging of nanoparticles with a TEM depends on the contrast of the material that you are analyzing compared to the background. TEM grids are prepared by drying nanoparticles on a copper grid that is coated with a thin layer of carbon. Materials that have different electron densities than the amorphous carbon film are easily imaged (for example, silver and gold) whereas polymers or biomolecules that have similar electron densities to amorphous carbon can be difficult to image.

• High Contrast / Easily Imaged:
  • Most metals: gold, silver, copper, aluminum
  • Most oxides: silica, aluminum oxide, titanium oxide
  • Particles made from polymers
  • Carbon nanotubes, quantum dots, magnetic nanoparticles
• Low Contrast / Difficult to Image
  • Biomolecules / Dendrimers
  • Some polymers

If you’re unsure whether your sample is appropriate for imaging please contact us.

To obtain high quality TEM images often requires optimization of sample preparation techniques that are specific to each material that is being analyzed. There are many factors that can influence the quality of the image.The more information that you can provide on your sample the higher the chance thatour first pass atimaging your sample will be successful. We highly suggest that you perform the following steps when preparing your sample for TEM imaging:

• Provide the nanomaterial in a pure state.The grid preparation involves the drying of your sample onto a grid and all residualsalts, polymers, biomolecules, or other particulates will be dried and imaged along with your nanoparticles. Highest quality images will be obtained when you can isolate the nanomaterial from all residualreactant components using centrifugation/wash steps, filtration, or dialysis.
• Provide as much information as possible with your sample. Details on the size, shape, material, and concentrationas well as the solvent and the concentration of residual reactants will help us determine if the sample needs additional processing before images can be obtained.

For questions about sample preparation please contact us.

In some cases, the images will be different from what you are expecting. This can be due to a wide range of reasons including sample preparation, residual reactants, or low concentration or low contrast of the particles. Options for next steps:

• Re-imaging: In some cases, simply re-imaging the sample at a lower/higher dilution or capturing additional images will provide the data that you need. Send an email to service@nanocomposix.com describing what you would like to achieve. A new sample will be prepared and an additional TEM analysis charge will be billed to your order.
• New Preparation: Preparation optimization can be extremely challenging for TEM samples. Typically, nanoparticles are dispersed in a compatible solvent and drop cast on a carbon coated TEM grid. Residual chemicals in solution can coat the nanoparticles during the drying process. A number of different techniques can be tried to improve the sample quality image. Contact info@stratech.co.uk to set up a time to discuss your sample and the potential for achieving better images. We’ll provide a quote for the preparation optimization.
• Sample Processing: Depending on your sample, it may not be possible to obtain high quality images in the as received form. Washing the nanoparticles may be necessary to isolate the nanoparticles from other residual reactants. Contact info@stratech.co.uk to set up a time to discuss sample processing that may generate improved images.