Hi, I am doing DNA conjugation onto 15nm gold nanoparticles using the freezing method. However, after overnight incubation gold nanoparticles turn blue (even without adding any salt).
I wonder if anyone has any idea about what the reason is.
Thanks in advance.
Kübra
Hi Kübra Kontbay ,
Gold nanoparticles can turn blue after overnight incubation at -20°C due to temperature-induced aggregation. At lower temperatures, the thermal energy of the particles decreases, weakening the stabilizing effects of surface ligands or capping agents, which typically provide electrostatic or steric repulsion to prevent aggregation. Consequently, gold nanoparticles come closer together, leading to aggregation driven by attractive van der Waals forces. This aggregation alters the way the nanoparticles interact with light, causing a shift in their plasmon resonance absorption peak from the red to the blue region of the spectrum, resulting in a change in color. The specific behavior can vary depending on factors such as nanoparticle size, shape, surface chemistry, and surrounding environment, and the phenomenon is often reversible by returning the nanoparticles to a higher temperature or adjusting solution conditions.
Hi Rajaiah Alexpandi,
Thank you so much for the info. Maybe I need to change the size of the AuNPs first.
Hello, I have a different opinion on this phenomenon. The problem is in freezing of water and its crystallizaton at -20C . This leads to increase of concentration more than 6 times and also it may change pH of the solution and therefore aggregative stability. Yes, low temperature increases formation of hydrogen bonds. In order to overcome the issue with aggregation you need to add to the solution antifreeze and store it at -10C in a supercool state. I did m some work with freezing of solutions with AuNPs
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