I have noticed some discussion about using microscopy to determine particle size of CS. I would like to add this information in case it has not been discussed in the past.
The resolution of a light microscope is limited by the wavelength of light and can be determined roughly by the following formula: R = (2)(wavelength)/(2)(numerical aperture) R is the resolution (i.e., minimum size that can be resolved visually) To find the resolution of a light microscope we can use the following values: Numerical aperture = 1.3 (approximate value of the highest quality high power objectives) wavelength of green light = 0.5 microns Then the equation becomes: R = (2)(0.5 microns)/(2)(1.3) R = 1/2.6 or approximately 0.5 microns. In other words, the smallest particle that can be clearly seen in a light microscope should be about 0.5 microns in diameter. Anything smaller than this can not be measured directly as I know from personal experience. There are some other light microscopy methods that can be used to estimate size below the limit of resolution and these are based on light scattering methods. A dark field microscope could be useful in this case (I have seen some discussion on this). I have no extensive experience with these methods. I happen to have a good light microscope and would be willing to help you with your research efforts if you would like. I have phase contrast and dark field condensers and a Sony video camera and monitor. I can also feed the image into my computer to capture digital images. Btw, you can convert a regular microscope condenser to dark field by fitting a disc stop of appropriate size to the condenser. I could supply more info on this to anyone interested. You could call this an economy dark field condenser. I have also used electron microscopes to a limited extent. I have noticed some talk about obtaining an electron microscope. It has been some years since I have used one, but the instruments I have used were very expensive. Unless recent breakthroughs in electronics have yielded significant price changes in electron microscopes, I doubt that it would be possible for this group to obtain one. I think your best bet is to contract the work out, which would be much more cost effective. If I can be of any further help I would be glad to participate in your research efforts. I have a Ph.D. in soil microbiology and have conducted research on symbiotic bacteria of agricultural significance. Unfortunately, I have no experience with bacteria that are pathogenic to humans. Jeff La Favre -- The silver-list is a moderated forum for discussion of colloidal silver. To join or quit silver-list or silver-digest send an e-mail message to: [email protected] -or- [email protected] with the word subscribe or unsubscribe in the subject: line. To post, address your message to: [email protected] List maintainer: Mike Devour <[email protected]>
