Polyvalent DNA gold nanoparticles are colloidal gold whose surface is modified with thiol capped synthetic DNA sequences. They were discovered by Chad Mirkin

Chad Mirkin

Chad A. Mirkin is an American chemist. He is the George B. Rathmann Professor of Chemistry, Professor of Medicine, Professor of Materials Science and Engineering, and Director of the International Institute for Nanotechnology and Center for Nanofabrication and Molecular Self-Assembly at...

 et al. at Northwestern University in 1996. Due to the strong interaction between gold and thiols (-SH), a single monolayer of DNA around the gold particle can be obtained. The negative charge repulsion of the phosphate backbone of DNA orients the DNA strands out into solution with a unique footprint that is dependent on gold nanoparticle size and packing density. Image)

Simply by positioning many strands into close proximity, these particles possess novel properties in which the independent DNA strands do not. Due to the cooperative effects of the polyvalency of multiple DNA strands, DNA on a particle has a stronger and sharper melting temperature when binding to its complement compared to DNA free in solution. Because of this effect and the unique optical properties of colloidal gold, various DNA detection technologies have been developed.

Synthesis

Gold nanoparticles can either be purchased or synthesized from a variety of methods.

1. Reduce the DNA into thiols by adding 0.1M solution of DTT and 0.18M phosphate buffer (PB) (pH=8) for 1 hour
2. Purify the DNA via a NAP-5 column
3. Add DNA to gold nanoparticles at a concentration of 10OD/mL
4. Bring the concentration of sodium dodecyl sulfate (SDS) and PB to a final concentration of 0.01% and 0.01M, respectively
5. After 20 minutes, bring the concentration of NaCl to 0.05M using a 2M NaCl and 0.01M PB stock solution while maintaining 0.01% SDS and incubate for 20 minutes
6. Repeat step 5
7. Increase the NaCl concentration at increments of 0.1M until a final concentration of 1M is reached over 20 minute increments
8. Incubate overnight
9. Centrifuge down the gold nanoparticles and remove supernatant and resuspend in a 0.1% SDS solution
10. Repeat step 9 four times