The gold nanoparticle was purchased from the company and the concentration was given as 6.0E+12 particles/mL. I was wondering if I can simply use Avagadro's number to convert it to nanomolar. The down path of the use of gold nanoparticle is to be diluted with distilled water to 0.4nM and perform nanoPCR.
Yolanda Lin You can state the concentration in any form you wish with an assumption of the size and shape (usually spherical) of the particles present and the density of gold. There are a number of previous questions on RG asking the same thing that you can find with a search.
Do not dilute with DI water. Almost certainly you'll cause the particles to aggregate and agglomerate settling out of the system. That's because you're washing out the stabilizers and other materials that keep the colloid particles separate, apart, and stable.
Thank you for the answer! i wanna ask what kind of diluent would you suggest if the gold nanoparticle is suspended in citrate buffer.
Yolanda Lin The ideal diluent is the continuous phase that the particles are residing within. In cases that you're making the material, then this could either be obtained with knowledge of the constituents, (ultra)filtration, or centrifugation. Ask the manufacturer of the gold colloid what would be an appropriate diluent (if any; the system may have to be used 'as is'). If you know that the particles are suspended in citrate buffer and the concentration of that buffer, then this would be the appropriate diluent (if no other ingredients).
In terms of your original question, calculate the mass of a single particle of gold based on the size (pi/6).d3.rho (where d is the diameter and rho the density of the gold. If you use 19.3 g/cm3 for the gold density then the diameter needs to be in cm). You then know you have 6E12 total particles so you can then work out the mass of gold present in the system. This is easily converted to molarity (mol.L-1) Only issue is getting the units correct.
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