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Finis Ramanii

In our March issue we had demonstrated the evidence of carotene in tardigrade "tuns" (tardigrades in the dry state) on the basis of Raman spectroscopy. Furthermore, we were able to show that moss (the classical tardigrade nutrition source) contains carotene. As a consequence we can assume that the red Echiniscus tardigrades are able to enrich the carotene in their body.

The following subject of investigation shouldn't be taken seriously. It will just help as an illustrating object in order to provide some practical measurement hints. Let's have a Raman look at the "Kaiyodo Takara" tardigrade 3D model which was presented here in our May 2014 issue.

[ Tardigrade 3D model under the Raman microscope ]

Fig. 1: Just for the fun of it - the "Kaiyodo Takara" tardigrade 3D model under our DIY Raman spectrometer microscope. The green laser light is being focused on the object from top, through the microscope objective. The backscattered and Raman signal bearing light is reflected through the same microscope objective optics and is being evaluated further above, by means of the spectrometer.

Well, one might proceed as shown in the image. The sad news is that the inner colored parts of the model are showing strong fluorescence which is overwhelming our Raman signals. As a consequence you will need some creativity and patience to direct the laser light onto the object in a manner that the disturbing parts of the models do not become activated. And in fact it is possible then to gain a spectrum which is not spoiled by fluorescence:

[ Raman spectrum of the tardigrade 3D model ]

Fig. 2: Raman spectrum of the colorless resin which makes up most of the "Kaiyodo Takara" tardigrade 3D model. The interpretation is not easy (at least for us). It appears that the resin doesn't contain aromatic rings which attached hydrogens, otherwise we would get so-called C-H stretching bands at Raman shift values beyond (higher than) 3,000 (cf. the polystyrene spectrum in our recent issue). On the basis of the general attitude of the spectrum we can exclude PMMA as well. On the other hand there is an ester band at a Raman shift value of ca. 1,720. And there exists some similarity with polyester resin Raman spectra. But, of course, many synthetic resins do contain ester groups, so we should be cautious with respect to an analytical verdict ...

Here are some more final hints for those who are still willing to participate actively:

(1) It makes sense to have an "easy going" specimen at hand which can serve to check the basic function of our setup. For this sake we are recommending carotene capsules from the grocery store. They can be opened and their content squeezed onto an ordinary slide, and protected by a cover glass. The intensity values reached with this specimen should be noted for later reference. Raman spectroscopy does only work with perfect laser adjustment. So adjustment will take some time and carotene will be helpful.

(2) The typical total measurement times with our setup are in the range of ca. 20 seconds to one minute. They might be made up of e.g. of 10 runs, each lasting 6,000 milliseconds, summing up to one minute in total. The background noise (the signal without the laser) must be subtracted manually when using the "Spectrum Studio" software. Only then you will get clean spectra. More expensive software might perform the background subtraction automatically.

(3) Longer measurement times will cause additional noise problems: some pixels of the spectrometer might behave erratically. You will have to experiment and find out the optimum measurement time for your single runs. This is clearly a drawback of our simple setup. Professional spectrometers might behave much better in this respect as most of them are being cooled actively. As a consequence measurement times might last 20 minutes or longer with those instruments - which results in a much better signal to noise ratio.

(4) Please keep in mind that the laser light is not only dangerous for your eyes. It might ruin the specimen as well. Minerals will cause no problems but living micro organisms will be harmed or killed by strongly focused, high intensity laser radiation.

© Text, images and video clips by  Martin Mach  (webmaster@baertierchen.de).
The Water Bear web base is a licensed and revised version of the German language monthly magazine  Bärtierchen-Journal . Style and grammar amendments by native speakers are warmly welcomed.

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