February 03 2018 by Drew Haser

Nanoparticles are small, but how small? To put things in context consider a gold bar. Without doubt, we can all image a gold bar - they are international symbols of wealth, the target of many heist movies, and something we'd all probably like to get our hands on.

If we were to stroll into Fort Knox or a Federal Reserve Bank and pick up a gold bar how much gold would we actually be clutching? Well, according to the London Bullion Market Association (the organization that sets the worldwide accepted benchmark standards) an acceptable gold bar is called a Good Delivery bar and should weigh between 350 and 430 troy ounces. The most common weight is 400 troy ounces, which equates to 12.4 kg - or just over 27 pounds.

 

So how does a 12.4 kg gold bar compare to gold nanoparticles?

Taking colloidal 20 nm gold nanospheres for example, with a standard Optical Density concentration of 1 (Optical Density defined) there are 52 micrograms of gold per milliliter of dispersion media.

Thus to achieve the same mass of gold in 1 gold bar, you would need 238,461,538 mL of colloidal gold nanoparticles!

 

Put differently, imaging filling a 2.5 million liter Olympic size swimming with 20nm colloidal gold nanoparticles.With the pool completely full you would have the same amount of gold as only 10.5 gold bars. Compared to the 2.5 million liters of gold nanoparticles, the corresponding volume of the gold bars is only 0.6 liters, small enough to fit in a small backpack or briefcase - although it would be heavy to carry! 

Curious about how the math works out for other gold nanoparticle sizes? Use our conversion chart to get the mass of other gold nanoparticles from 5 nm to 120 nm and compare for yourself.