General

I only want 1 ml of your nanoparticles to evaluate.  Why is the smallest volume you sell 100 ml?

Our products demand a very high level of quality in the preparation and packaging prior to shipment.  This is very time consuming and expensive. To help our customers in the evaluation of our product, we provide extensive data on our website.  Further, we provide introductory kits for both our spherical gold and our gold nanorods.  These come with four different sizes of 25 ml each, perfect for evaluation.

What is the concentration of your particles?

For our spherical gold nanoparticles, the concentration as a function of nanoparticle size is listed in the spherical gold data sheet.  For our nanorods, we list those products by weight percentage.  To convert weight concentration (mg/ml) to particle concentration (nps/ml), or to convert our spherical gold particle concentration to weight concentration,  and for other handy conversions, download: FAQz conversions.xls

Why do my spherical nanoparticles all appear red?  The 30 nm particles have a peak absorbance (absorption and scattering) at 523 nm, right in the middle of the green.  Shouldn't they be green?  Shouldn't the 80 nm spherical gold nanoparticles, with an absorbance peak at 550 nm appear yellow?

Great question, one that few truly understand.  For a complete explanation of absorption, scattering and transmission, please see our upcoming tech note.

Spherical Gold

Are your colloids pure gold?

Yes, with a capping agent.  In order to correctly grow in solution, all nanoparticles require a capping agent.  Like citrate, our patent pending method utilizing a proprietary capping agent that is also a carboxylic acid.  However, our capping agent results in highly monodisperse nanoparticles with a reduced surface charge, both of which are highly advantageous properties in nanotechnology applications.  Like citrate, our capping agent is easily replaced with chemistry or electrochemistry.  This includes simple adsorption of antibodies to the surface, as well as more complex chemistries that involve thiolated attachments.

I notice that your nanoparticles settle out of solution when stored for weeks at a time.  Is this normal?

Especially for our smaller nanoparticles, the reduced surface charge of our nanoparticles, though highly advantageous for attachment chemistries and for reducing charge induced non-specific binding, can result in settling.  There are two types of settling, reversible and irreversible aggregation.  If stored under the proper conditions, settling of our particles is reversible and the nanoparticles are easily resuspended with a gentle shaking motion.

How do you calculate the size distribution of a batch?

We sample 20-30 nanoparticles from multiple TEM pictures.  Using different imaging techniques, we calculate distribution curves manually.  We do this for every batch manufactured.  Our product specifications have been confirmed in a study by the NIH/NICHD, and by hundreds of customers.

How long does it take to manufacture a batch of spherical nanoparticles?

Although our manufacturing methods are highly characterized and completely automated,  in order to make nanoparticles with the reproducibility we require is no slow task.  Some sizes of our nanoparticles take up to nine days to manufacture.

What is the shelf life of your spherical nanoparticles?

If stored and handled correctly, the shelf life is > 1 year.  We have been manufacturing our nanoparticles for over two years and have yet to see a definitive lifetime.

Gold Nanorods

I notice your nanorods can be just about any color, not just red like the spherical gnps.  Wouldn't this have great applications in multichannel lateral flow?

Yep.

I purchased your bare Nanorodz^TM product and notice that the solution is not entirely clear.  What is this?

Rather than a carboxylic acid capping agent, nanorods use a CTAB surfactant.  This surfactant not only provides the means for manufacturing but also keeps the nanorods suspended in water.  Just like the carboxylic acid, CTAB is easily replaced with your surface functionalization.

This is the structure for CTAB

Theory is that it forms a bilayer.  If it is completely linear, then the bilayer thickness would be ~6nm