I am trying to replicate DNA stabilized silver nanocluster formation and visualize the various fluorescence. However, when I dissolve silver nitrate and mix it just with phosphate buffer (pH 6.7) or citrate buffer (pH 7.0), there is an immediate change in color even without reducing agent, NaBH4. (Silver Nitrate 100mM, both buffers 20mM)
When I mix it with phosphate buffer, it turns to opaque yellow and in citrate buffer, it turns to opaque white. Does this normally occur? For some reason, even with the addition of specific DNA oligos, there is no absorbance or fluorescence detectable, so I'm guessing it's because of the described problem.
Do you have any ideas?
i think almost all silver salts are insoluble in water except nitrate so would expect phosphates and citrate to precipitate so I am sure that both of the above are correct that only solutions in high quality water are stable
Yes, Ag ions may form coordinate complex in the buffer solution, where DNA oligos were in solution it may shift either blue or red. So, absorbance or fluoresce might not be detectable or might be detectable if you correct the lamda max in absorption spectroscopy or excitation prompt wavelength by scanning the excitation.
Yes it isn't stable in citrate buffer. You should be using water as your solution, not buffer. Silver nitrate is quite stable in water. I keep it at 4oC in the dark and it is still clear after 6 months and counting. Is there a reason that you need buffer?
I've just googled DNA stabilised silver nanocluster (I hadn't heard of them) and the first paper I clicked on clearly says in the methods for nanocluster formation that water was used.
Article DNA stabilized silver nanoclusters as the fluorescence probe...
i think almost all silver salts are insoluble in water except nitrate so would expect phosphates and citrate to precipitate so I am sure that both of the above are correct that only solutions in high quality water are stable
Thank you for the answers!
For dissolving the silver nitrate, I do use water, but in the papers I'm referring to, they use buffer solutions when mixing it with the DNA.
In the paper ,"A complementary palette...", after mixing the DNA and dissolved silver nitrate in phosphate buffer, they specifically state that NaBH4 is used to cluster the silver particles after (they also mention color change after addition of NaBH4). So I guessed that silver remained stable in buffers, unless NaBH4 addition.
Article A Complementary Palette of NanoCluster Beacons
Article Multiplexed Analysis of Genes Using Nucleic Acid-Stabilized ...
Article DNA-Templated Silver Nanoclusters for Multiplexed Fluorescen...
The AgNO3 solutions is routinely apply for checking impurity of water and changing color is normal. you could simply compare your experiment results with buffered silver nitrate or with aquatic silver nitrate solution.
Yes they do change colour; i used silver nitrate in nutrient broth for exposing sublethal doses to cultures of Psuedomonas aeruginoas; firstly the silver precipitates and forms the chloride salt so cover buffers in silver foil and store in amber glass bottles; secondly the bacteral cultures on growing tended to accumulate the silver ions which over a period of time diminshed in the colony size and changed colour from fluorescent blue/green to dark brown reflective of oxidation of silver on exposure to light i beleive. the cultures adapted over a period of 12 months but the morphology of cultures changed. I dont know how this helps you but hope it sheds some light.
Citrate by itself is a reducing agent an it will help in the formation of silver nanoparticles. Like NaBH4.
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