We are trying to make lipid double-layers on different substrates and investigate lipid properties, but in most cases we can't detect the fingerprint band around 2900 cm^-1: we found literature comments on 'vanishing band due to thermal aging' (like 39 deg for 40 days): is it possible that excess laser spot intensity may 'burn' and make the band disappear? Or it may depend more on polarization? (actually using s polarization).'
we see even nice spectra (just some background, which I suppose be due to the substrate fluorescence, this is anodic porous alumina, APA). But we see no the expected band at 2900... what we see instead, for example, with same lipids on flat gold (not on gold coated on APA). Our student Amir will soon post example spectra here, for discussion...
thank you!
I attached the Specta here:
First spectra: the Flat Au incubated with POPC dissolved in isopropanol and then washed with PBS.
Second Spectra: Our APA with 500nm thickness, coated with Au and incubated with MBA, then washed and dried. DOTAP vesicles with 200 nm size are extruded in PBS. Then, incubated overnight.
Dear Yuriy,
thank you so much for your useful comments.
I was not aware of the close resemblance of IPA to our spectra, good remark that you pointed out to our attention! Obviously, the multiple band around 2900 cm^-1 (which is the C-H stretching, mainly) is found also in IPA, same as in many other organic compounds, and is not specific of lipids.
We will look, then, for the fingerprint of each different lipid around the regions you have pointed out where minor different peaks appear in our spectra, namely ~1650 and 2125.
At the same time, I wonder why should these band appear, when due to IPA residuals, on using linearly polarized light... We expect to see some features due to the lipid phase order and related polarization (in the same plane as the lipid - supposed! - double layer, which should not appear in case of disordered (not layered) lipid of any other compound with yet similar composition...
I'm obviously missing something on how the polarization works... We will try to open our Renishaw Invia and remove the polarizer, if possible, and repeat the measurements.
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