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Sebastian Götz (promotion date: 31 May 2006)

Wavelength resolved detection of quantitative analyses on chip separations

Promotion Date: 31 May 2006

Sebastian Götz

We are an analytical group, we are measuring things. We do separations of substances, e.g. environmental pollutions or whatever.
If you measure these substances on small glass microchips, you have the benefit of fast separations and you only need a very small amount of your sample.
So the last years a lot of effort has been put in this type of chip, were compounds in fluids are separated by chemical electrophoresis (a very high voltage on the chip make the analyte ions travel in the direction of the charge. Some travel faster than others depending on the size of the ions, thus effecting separation). In order to detect the substance we are looking for we attach a ‘label’, a fluorescent molecule.

What was your thesis about?

We are an analytical group, we are measuring things. We do separations of substances, e.g. environmental pollutions or whatever. If you measure these substances on small glass microchips, you have the benefit of fast separations and you only need a very small amount of your sample. So the last years a lot of effort has been put in this type of chip, were compounds in fluids are separated by chemical electrophoresis (a very high voltage on the chip make the analyte ions travel in the direction of the charge. Some travel faster than others depending on the size of the ions, thus effecting separation). In order to detect the substance we are looking for we attach a ‘label’, a fluorescent molecule. We do that before the fluid is guided through the chip. In the separation process you don’t see all the other substances go by, but only the one that fluorescence, without any background.
This allows excellent quantification of the substance you are looking at. We also know what sort of spectrum of light it should produce and when it differs we know that there is another substance involved.

It all sounds complicated. Are there no other detection methods for substances in fluids?

There are. If you have all the money or all the space you can use other methods.
You could then buy a mass spectrometer that fills the room at a price ranging from 500.000 to 1 million Euros. Because of this you will always have different approaches to detection.

What was your specific contribution in this line of research?

Fluorescent detection is very common, also on chips, because it gives you very nice limits of detection. Laser is often used because it gives you a high concentration of light per area. The disadvantage is that you are very fixed, because a laser has only one wavelength (some have two). But you cannot use the same wavelength for all analytes, then you have to use another laser, which are usually quite bulky or expensive or both. Our approach was to add some flexibility by using a rather ordinary lamp as an excitation source. With one hand stroke you get different wavelengths by adding filters.

But a lamp is not as focused as a laser beam.

Yes, that is a drawback and the price you have to pay for being more flexible.
You lose the extremely low limits of detection.

What are the possible applications?

Quite a wide range of separations. I separated the taurine in Red Bull (a sports’ drink). We also looked at depilatory cream and permanent wave cream.

Did you encounter any problems during your PhD?

We did not build the components for our system ourselves. It took some time for them to arrive and we also needed a special camera sensitive and quick enough to record all the data. That also took up time. Since we are a chemical analysis group all the technical work was a bit of a problem. And I was the first one to start on the subject and had no one to back me up. But I actually enjoyed finding out all these things by myself. The only thing is that I do not have such a big book, since there aren’t that many results. But I think that is the essence of PhD work, not only being a specialist in your own field, but getting the ability to do the work outside of your specific area as well. Having had a fairly tough PhD time gives me a good preparation for work in industry, where you quite often have to start from zero as well.