Tardigrades, carrot carotinoids and the DIY Raman spectrometer

Do you feel tired when coming across those millions of social media messages loaded with destructive emotions on one hand and virtually no content on the other? In this case you should turn your attention to a more relaxed scenery like the one in our magazine #200 - with perfectly concentrated, hate-free tardigrade-related content!

Figure: tardigrade "tun" (tardigrade in the dry state) investigated by means of a DIY Raman microscope spectrometer. The red curve is depicting the Raman spectrum of an Echiniscus sp. tardigrade in the dry state, measuring about 50 µm in length. It was created by simply focusing from top onto a tardigrade tun which was positioned between slide and cover glass (no water!). The black curve is showing the Raman spectrum of a carrot slice, for comparison.
In both spectra you will perceive similar bands bands at Raman shifts of ~1150 and ~1510 cm^-1 which have to be attributed to the bands of the carotinoids (see below). This means that we are able to make plausible that the orange colour of the Echiniscus 'tuns' is actually caused by carotinoids (the bands below 600 are due to our very modest instrumentation and therefore do not contribute any further information).

We hope that some questions might arise now somewhere within the brains of our readers. These might be:

Q: The tardigrades can not be made up of carotinoids only. Where are the proteins, lipoids and other biochemical constituents? Why are they not showing up in the spectrum?
A: When being illuminated by a green 532 nm laser (as the one used in our DIY instrument) the carotinoids are showing a so-called Raman resonance. Due to this Raman resonance the bands of the carotinoids are strongly enhanced. All the other biochemistry should give some signals as well but these are overwhelmed by all kind of spectrum noise including fluorescence.

Q: I do know Ramen quite well, this is an indian noodle speciality dish, isn't it, or japanese? Frankly speaking I don't care. But what is the relation between noodles and analytics?
A: We will discuss the basics of Raman spectroscopy in one of the subsequent issues of our magazine. At the moment it might be sufficient to explain that the object unter investigation is irradiated by means of a laser beam (a strong light with an extremely narrow wavelength range). More than 99,9% of this light is merely reflected by the object and so its wavelength remains unchanged. But a very tiny fraction of the light is frequency-altered by the object thus bearing some of the chemical information 'seen' on its pathway. As a consequence the Raman effect will cause a result spectrum with a very strong (unchanged) laser signal and small satellite signals the wavelengths of which are slighty shifted. Only the satellite pattern is used for chemical interpretation whereas the strong laser signal must be filtered out. Otherwise it would ruin the spectrum.

Q: Well, you are kidding: how should it be possble to analyze microscopic objects when the laser has to pass through a cover glass?
A: In fact it works in the same way as the safety control at the airports. Also in this case a laser beam is focused through the transparent walls of your liquids' bag and returns with information about its contents.

Q: Hi, I am in a hurry, simply send a detailed plan how to build this instrument!
A: Please be patient, all relevant information will be presented in the following issues.

Q: How much money did you spend for the components of your Raman spectrometer?
A: Without microscope and computer, ca. 600 US$. But of course you should keep in mind a considerable investment for the computer: we are using a high-performance "Dell D600" notebook (at least it was top notch in 2004 ;-).

© 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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