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Water purity and nanoparticles on Mica

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Don Chernoff posted on Tue, Jan 22 2013 9:59 PM

I'm studying nanoparticles in aqueous solution.  The particles are in the

range 1-5 nm diameter.  My task is to image them by AFM and to measure the

height of many individual particles.  The sample preparation procedure is

basically to apply a droplet of the suspension to freshly cleaved mica,

rinse and dry with nitrogen gas.  The AFM images are made in air at room temperature using

TappingMode (intermittent contact) and obtain nice images. However, blank

samples prepared from the ultrapure water used as diluent and as rinse water

also show some particles.

I have tried more than 3 different samples of ultrapure water produced using

Milli-Q water purification systems at 3 different labs and gotten similar

results.

I believe that other people have had similar problems.  I found a thread on this forum dated Jan 7, 2010.  The poster recommended BPC Grade water from Sigma (W3513 - Biotechnology Performance Certified) and also mentioned “The other source of impurities we found was the nitrogen stream used to dry the samples after washing. What exactly these particulates are we never found out, but by  running the nitrogen through a simple, home-made bubble trap, they largely went away.”

 

Can someone tell me what is meant by “bubble trap” and what type of filter one should use for the nitrogen stream?

 

I welcome all answers and comments.

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The water I use is "water for molecular biology", the item code for this is W4502.
If this differs from W3513, I cannot be sure, it looks quite similar on the sigma site. But I have tried another water they sold "water for cell culture" W3500, and it was not as good as W4502.

The bubble trap I never used. When we dry we use Argon at the moment, but I do not know why it would be any different in terms of particles compared to Nitrogen. The Argon is just what we have in the lab. I do not filter the argon, and I do not think i've seen particles from the gas when I do use it, but cannot be sure.
That work I mentioned on my website was allowing the WHOLE droplet to dry it self onto the surface, and then imaging. no blowing off.You need really pure water to do this and see nothing.
Another check for particles is doing size analysis in the DLS. With the Sigma water, the instrument gives us an error, because it cannot detect anything.if I ever got a result, I would throw the water away.
The Sigma W4502 water is good value for this sort of experiment, a liter will last along time if you are very careful with it (never put anything in the bottle).
Pete.

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Peter, thanks very much for your reply.  How do you store the water?

Moderator:  I wonder if there is any way to contact the other participant in the thread of Jan 7 2010.

-Don

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I think "bubble trap" probably refers to something like this: http://en.wikipedia.org/wiki/Gas_bubbler

where the idea is that particulates get stripped from the gas as it passes through water in the bubbler.

I did this years ago to try to get a humidified gas stream. That took some extra effort to increase the gas-liquid contact area and contact time using some small packing material in the flask and a fritted glass diffuser. But for the application here, just a flask, a two-hole stopper and two pieces of rigid tubing would do the job, where the inlet is longer and below the fluid level and the outlet is shorter and above the fluid level.

 

Regards,

 

-Ben

 

 

 

 

 

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Ben,

Thanks for the link to Wikipedia "gas bubbler".  In my application, using the N2 gas to remove water from a mica surface, it does not make sense to me to bubble the N2 through a liquid.

Can the (anonymous) person who posted this idea in 2010 comment?
-Don

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Don,

I think you would find that the gas humidity will not increase substantially with just one pass through a simple gas bubbler. So it will still be suitable for drying a sample. I should have made that point more explicitly. It's why I mentioned that additional effort is required in this sort of configuration if you do want to introduce substantial humidity in the gas stream.

-Ben

 

 

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Don, I just keep the water close din the fridge. the main thing is to only pour out of the bottle, and keep it closed as much as possible.

It should last OK at room temperature as well...

Regards,

Pete.

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Hi Don,

I would agree with Peter. DLS will help to exclude either water or the nitrogen as the source of contamination. Rinsing of the sample facing a sink or rubbish bin followed by the careful drying either in air or on the hot plate under a Petri dish should work well. "Air gun" with "clean" gas can be a source of contamination that can be excluded.

More ideas can be found at MIAWiki by the permalink: http://confocal-manawatu.pbworks.com/w/page/63044408/Water%20for%20AFM%20Imaging

Your comments and suggestion would be highly appreciated.

MIAWiki has other related knowledge nodes like http://confocal-manawatu.pbworks.com/w/page/41903251/Particles%20Fixation%20for%20AFM that may be of interest to you.

If you like, I could assist you in your experiment remotely via Skype: http://confocal-manawatu.pbworks.com/w/page/23665663/Dmitry%20Sokolov

Cheers,
Dmitry
MIAWiki Knowledge Network /
Online Consultancy on Microscopy and Image Analysis

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Dmitry,

Thanks for your comments.  Unfortunately, I don't have a DLS at my lab.  I like your suggested alternative to blow drying and plan to try that with the Sigma 4502 water.
I notice that the article "Particles Fixation for AFM" is written by another Sokolov (Igor, of Clarkson Univ. in USA).  Perhaps you should comment about this.

Don

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