Changing the size of nanoparticles

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ryanum
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Changing the size of nanoparticles

Post by ryanum »

Hello! I'm planning to test the size of silver nanoparticles on E. Coli and Lactobacillus. I need help in developing a procedure to alter and manipulate the size of silver nanoparticles. From a video that I watched on Youtube Making Gold Nanoparticles I am aware that a darker colour indicates the agglomeration of nanoparticles and thus an increase in their size. In this video, they used Sodium Chloride (NaCl) to increase the size of the gold nanoparticles in colloidal solution. Since I am experimenting with silver nanoparticles, I am wondering what solution I should use for the same effect to increase the nanoparticle size of my colloidal silver. My goal in the experiment is to test whether the size of silver nanoparticles correlates with an increased toxicity to the bacteria. Thanks for the help!

Ryan

I previously posted this question in the life, earth, and social science forum: viewtopic.php?f=28&t=15651&e=1&view=unread#p55146, but I was advised to move it here. Thanks! :)
norman40
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Re: Changing the size of nanoparticles

Post by norman40 »

Hi ryanum,

Your experiment sounds very interesting!

I have no experience with the preparation of nanoparticles. But I did find a procedure for preparing silver nanoparticles in which a sodium chloride solution is used to aggregate the particles.

http://education.mrsec.wisc.edu/278.htm

This part of the procedure appears to be similar to the gold nanoparticle preparation that you described.

Is it possible to purchase silver nanoparticles in different size ranges? If so that might be a reasonable alternative to attempting to make differently-sized particles yourself.

I hope this helps and good luck with your project. Please post again if you have more questions.

A. Norman
ryanum
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Re: Changing the size of nanoparticles

Post by ryanum »

Hi Norman,

Thanks for your response. I'm following the sciences buddies method for silver nanoparticles by purchasing colloidal silver, with the addition of manipulating their size. I could purchase preset sizes online, but it is very expensive! :D Any further input to answer my question would be much appreciated. Thanks, everybody!
norman40
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Re: Changing the size of nanoparticles

Post by norman40 »

Hi ryanum,

You could try adding a sodium chloride solution to a small amount of the colloidal silver recommended in the Sciencebuddies project procedure. A color change (as described at the link in my previous post) indicates particle aggregation. If this test works, you could prepare a larger amount of colloidal silver with added sodium chloride for use in the serial dilution experiment described in the project procedure.

You might consider testing the sodium chloride solution as a control since one of your colloidal silver samples will include it. My suggestion is to start with a sodium chloride solution of the same concentration as the one added to the colloidal silver. If this solution has no effect on the bacteria, there’s no need to test diluted sodium chloride solutions.

I hope this helps and good luck with your project. Please post again if you have more questions.

A. Norman
ryanum
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Joined: Mon Feb 01, 2016 9:39 am
Occupation: Student

Re: Changing the size of nanoparticles

Post by ryanum »

Hi! Thanks for the response.

I am wondering, however, what ratio of colloidal silver (500ppm) to sodium chloride do you recommend? The starting size of the colloidal silver is about 10 to 20 nanometers. Ideally, I want to have a range of silver nanoparticle sizes from 10 to about 100 nanometers. I do not have the equipment like a scanning electron microscope to measure size, so is there a sort of calculation that can be done to determine the size of the silver nanoparticles after adding sodium chloride. I have five jars to prepare serial dilutions of NaCl to alter the AgNP size. I am also wondering, what reducing agent is best to make the nanoparticles even smaller, as this can also be an option for me. Lastly, what exactly are capping agents? Are they necessary too? I can elaborate and explain my questions further. Thanks!

Ryan
norman40
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Re: Changing the size of nanoparticles

Post by norman40 »

Hi Ryan,

I don’t know what amount of sodium chloride to add to your colloidal silver. I suspect that any effect of sodium chloride addition depends on the silver concentration. My suggestion is to make a 1.5 M solution of sodium chloride and add a few drops to a small amount your colloidal silver to see if you get a color change. As you are conducting this preliminary test, keep track of the starting volume of colloidal silver and the volume of sodium chloride solution that you add. If the test works, you can use this information to scale up your silver/sodium chloride mix to the volume you need for your experiments.

I’m not aware of any calculation that relates silver particle size to amounts of added sodium chloride. Someone may have reported such a correlation and you might try a search with Google Scholar to see if something turns up. Otherwise, you might try contacting a local university to see if someone there could provide particle size measurements. Finally, you may find that purchasing silver nanoparticles with the size range that you want to test is a reasonable option.

A capping agent is a material added during nanoparticle preparation to stabilize the particles and prevent aggregation. A reducing agent is a chemical that serves as an electron donor in an oxidation/reduction reaction. In preparation of silver nanoparticles, a reducing agent is used to reduce silver ions to the metal.

I hope this helps. Please post again if you have more questions.

A. Norman
ryanum
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Joined: Mon Feb 01, 2016 9:39 am
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Re: Changing the size of nanoparticles

Post by ryanum »

Thanks again for the response. Do I need a capping agent in addition to my agglomeration agent, sodium chloride? I just want to make sure the nanoparticles size do not change after time once I alter their size. Would the size of the nanoparticles remain stable? Thanks!

Ryan
ryanum
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Joined: Mon Feb 01, 2016 9:39 am
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Re: Changing the size of nanoparticles

Post by ryanum »

Hi once again!

I was told that NaCl, the agglomeration agent, would not increase the size of the nanoparticles, but their aggregates. So, I'm wondering if the increased aggregate size would have a similar behaviour as if the nanoparticles are increased in size. Thanks!

Ryan
norman40
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Re: Changing the size of nanoparticles

Post by norman40 »

Hi Ryan,

Great questions. I don’t know if adding sodium chloride would cause a time-dependent agglomeration of the silver particles. But you could check a test solution (like the one I described in my last post) after several hours for color changes or precipitate formation beyond your initial observations. No changes after a few hours would indicate that you don’t need a capping agent.

I think that increasing nanoparticle size may well have effects that differ from increasing aggregate size. It’s possible that aggregated particles may interfere with the nanoparticle surfaces, making them less effective as catalysts or binding sites.

I found two review articles silver nanoparticles that may be useful to you.

http://www.sciencedirect.com/science/ar ... 5210000377

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4326978/


I hope this helps. Please post again if you have more questions.

A. Norman
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