FAQ

Table of contents:

Most Common FAQ

  1. I can’t find the material or size that I’m looking for.  Can you make it for me?
    We routinely fabricate custom materials for our customers.  Please see our Custom Synthesis page for more information.

  2. Can you coat nanomaterials with other capping agents or biomolecules?
    We routinely functionalize our materials with alternative capping agents or biomolecules for our customers.  Please see our Custom Synthesis page for more information.
  3. How are your materials characterized?
    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 >20 nm.   

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Nanomaterials

  1. I can’t find the material or size that I’m looking for.  Can you make it for me?
    We routinely fabricate custom materials for our customers.  Please see our Custom Synthesis page for more information.

  2. Can you coat nanomaterials with other capping agents or biomolecules?
    We routinely functionalize our materials with alternative capping agents or biomolecules for our customers.  Please see our Custom Synthesis page for more information.

  3. What is your production volume?
    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 see our Bulk Synthesis page for more information.
  4. What is the shelf life of your nanomaterials?
    Our stability guarantee is 6 months for NanoXact nanoparticles and 3 months for BioPure nanoparticles when our Storage and Handling guidelines are followed.  Longer stability can be expected, as we have been tracking material stability for 4 years and have yet to see appropriately stored materials destabilize. 

  5. My nanoparticles settle out of solution- is this normal?
    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. 

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Purchasing

  1. What types of payment do you accept?
    We accept payment by credit card (Visa, Mastercard, American Express), check, money order, and wire transfer.  All transactions must be completed in US dollars.

  2. What is your payment policy?
    We use standard NET 30 terms.

  3. Do you ship internationally?
    Yes.  We have provided materials to researchers in more than 30 countries, and ship our materials worldwide.

  4. Do you have an international distributor?
    We do not currently have any international distributors, however we do ship our materials worldwide.

  5. What is the average shipping time?
    Domestic orders typically arrive within 5 business days.  International orders typically arrive within 3-8 days. 

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Silver

  1. Do silver nanoparticles oxidize?
    Yes, silver will oxidize in the presence of sulfur and oxygen.  Please see our Nanotoxicology Knowledge Base for additional details.
     
  2. Are your silver nanoparticles amorphous or crystalline?
    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.
     
  3. How do I tell if the silver nanoparticles that I've purchased have gone bad?
    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.

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Nanoparticle Processing

  1. Previously I purchased Ag nanoparticles in water from you but they can’t be spin-coated due to the low viscosity. Do you have Ag nanoparticles in other suspensions which have higher viscosity, and thus are suitable for a spin-coating process?
    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.
     
  2. Are there alternatives to spin coating that I can use to create a monolayer?
    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.

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Plasmonics and Optical Properties

  1. What is the effect of different environments (e.g. water or air) on the spectrum of silver nanoparticles? How does shelling the nanoparticles with silica affect the spectra?
    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.

  2. I'm looking for a nanoparticle with specific optical properties.  How can I determine what particle size is most appropriate for my application?
    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!

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Quality Control

  1. How are your materials characterized?
    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 >20 nm.   
  2. How do you measure nanoparticle size and CV?
    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%).
  3. When I characterize your particles using TEM, I see a bimodal size distribution.  Aren't nanoComposix particles supposed to be monodisperse?
    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.  During the last 12 months, TEM grids with amine, thiol, and carboxy functional groups have become commercially available.  These grids can cause a reverse ripening process that results in a bimodal size distribution.  Therefore, we suggest that customers use formvar coated TEM grids.
  4. Why does my specification sheet list the hydrodynamic diameter and zeta potential as "N/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 <20 nm have very small scattering cross sections, and do not scatter enough photons to achieve reasonable signal to noise ratios in most commercially available instruments.  Rather than report a number that is inaccurate for these materials, we report N/A on our specification sheets. 

TEM Characterization

  1. What types of nanoparticles can be imaged?
    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.

  2. What information can I provide to maximize image quality?

     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 that our first pass at imaging 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 residual salts, 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 residual reactant components using centrifugation/wash steps, filtration, or dialysis.

    Provide as much information as possible with your sample.  Details on the size, shape, material, and concentration as 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.

  3. I received my images but they are not what I was expecting.  What options do I have?
    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: 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 service@nanocomposix.com 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 service@nanocomposix.com to set up a time to discuss sample processing that may generate improved images.

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