Posted by
Steffen Dietzel on
URL: http://confocal-microscopy-list.275.s1.nabble.com/Optical-Coupling-Gels-tp2518597p2520377.html
Hi Cam,
I had a respective problem on our multiphoton
microscope. Someone at last years FOM suggested
to use eye gel. So I ordered a collection of
various eye gels and Ultrasonic contact gels (is
that the English name for it?) from our pharmacy.
Price range: 2 - 5 Euro each, for the ultrasonic
gel this is for a 500 g bottle....
Inspired by a paper from Guy Cox, I used moss
from the lawn in front of the building (the snow
finally receded) as a test specimen (moss has no
air in the leaves, as have vascular plants),
first imaged in water for comparison. It turned
out that the eye gel brands I got had horrible
optical properties. But the Ultrasound contact
gel was not so bad. It even got better when I
diluted it 1:5 (or 1:10) in distilled water.
After finding empirically that it works, I
started looking for the ingredients. The material
data sheet (found on the web) stated it contains
25% 1,2 Propylenglycol, 74% water and 0.9%
"Pioneer NP 37". Futher Googleing revealed that
the later is a brand name for Na-Polyacrylat =
Carboxyvinyl-Polymere, a "Superabsorber"
For Propylenglycol, I found an Ri of 1.432 on the
web. For Na-Polyacrylat, I didn't find the Ri, so
I ignored it. Assuming I just can obtain the Ri
for my 1:5 dilution of the Gel (i.e. 5%
Propylenglycol in water) by calculation
(0.05*1.432 + 0.95*1.333), it is 1.338 and thus
not so very much different from water itself (I
know, I know, but I am not going for the
diffraction barrier in my application). I found
one reference that says the Ri of bovine muscle
tissue is 1.382 (Dircks JJ et al, J Biomed Opt.
2005, 10:44014), so what the sample is doing to
the optical path is probably much worse than what
this diluted gel is doing. (Makes me wonder if we
should ask companies for objektives made for that
Ri). Anyway, I am aware that this is a pretty
crude calculation with errors and unsubstantiated
assumptions, but the point is, I get images which fullfill the needs we have.
A note of caution: I use this now for a few weeks
only, so my practical experience is limited. the
1:5 dilution still slowly flows away, but at a
speed such that it is not a problem to "refill" in time.
I don't think you will get this particular brand
in Australia, but just for completeness the details:
Ultraschall-Kontakt-Gel Wasserfuhr, from Caesar & Loretz, D-40721 Hilden.
Diluting the Gel in 0.9 NaCl is not working:
Apparently the ions lead to a structural break-down of the gel.
And another note: Zeiss is selling something
called "Immersol W" which is supposed to be
viscous and have the Ri of water. No experience
with that one, I guess it can't beat the price of the Ultrasonic gel, though.
Let us know if you find alternatives.
Steffen
At 23:37 22.03.2009, you wrote:
>Hi List,
>
>Has anyone had any experience in using optical
>gels? We are looking at imaging lymphatic
>vessels in a mouse tail (still attached to a
>live mouse) and eventually lymph nodes with our
>two photon system. The scope is fitted with a
>20x water immersion lens (NA 0.95) but we dont
>want to submerge the whole tissue. So ideally we
>need a thick gel that has the same RI of water and wont damage the objective.
>
> I found one paper (Rothstein et al.) that use
> sorbitol gelled with carbomer 940 to create a
> gel with a refractive index similar to water.
> Is there any other gels that anyone has used
> before? I was thinking of acrlyamide
> (polymerised) but cannot find the RI of it.
>
>
>Cheers
>
>
>Cam
>
>
>Cameron J. Nowell
>Microscopy Manager
>Centre for Advanced Microscopy
>Ludwig Institute for Cancer Research
>PO Box 2008
>Royal Melbourne Hospital
>Victoria, 3050
>AUSTRALIA
>Office: +61 3 9341 3155
>Mobile: +61422882700
>Fax: +61 3 9341 3104
><
http://www.ludwig.edu.au/branch/research/platform/microscopy.htm>Facility
>Website
>
>
>
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--
---------------------------------------------------------------------------------------------------
Steffen Dietzel, PD Dr. rer. nat
Ludwig-Maximilians-Universität München
Walter-Brendel-Zentrum für experimentelle Medizin (WBex)
Head of light microscopy
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