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Spectroscopy recently spoke with Sergei Kazarian, professor of physical chemistry at Imperial College London (London, UK), about his research with FT-IR imaging.
recently spoke with Sergei Kazarian, professor of physical chemistry at Imperial College London (London, UK), about his research with FT-IR imaging. Prof. Kazarian is the coauthor of “Label-Free Chemical Detection in Microfabricated Devices Using FT-IR Spectroscopic Imaging” in the October 2012 issue of Spectroscopy.
Your article describes FT-IR imaging used as a detection technique with microfabricated microfluidic devices. What are the advantages of using this technique for in situ imaging of chemical processes compared with other techniques such as fluorescence microscopy?
Kazarian: The main advantage is that the chemical specificity of FT-IR imaging allows nonlabeled differentiation of substances on the basis of different chemical content, which is crucial for multicomponent samples or systems. So, unlike many other imaging methods this technique does not require labeling of the use of added dyes.
What are the key elements of the FT-IR imaging technique? Are focal plane array (FPA) detectors a necessity in this approach?
Kazarian: The key elements are the FT-IR spectrometer and focal plane array detector. An FPA detector is essential for obtaining chemical information from different locations within the sample simultaneously. An FPA detector is a multichannel detector, which typically consists of up to 16,384 pixels for measurement of thousands of spatially resolved spectra at the same time to generate chemical images.
Your study involved the use of both attenuated total reflectance (ATR) and transmission modes of sampling. What factors are involved in selecting one mode over the other?
Kazarian: Indeed, we use both modes. If information through the thickness of all channels is required than transmission is the method of choice. However, if absorption by a sample is too strong, then ATR mode may be beneficial, for example in studies of aqueous solutions. ATR mode has advantage of a possibility of probing different depths within the sample’s surface layer of several micrometer thick. The signal to noise is usually better in transmission mode because of the greater pathlengths that are typically used.
Your article mentioned the use of direct wax printing for creating microfluidic devices. What are the advantages and drawbacks of using this system to form the devices?
Kazarian: The flexibility is the main advantage of direct printing of mictrofluidic devices on infrared windows or crystals. This means that windows or crystals can be used many times and new designs of microfluidic devices can be easily created. So, it is a flexible, fast, and inexpensive method for preparing such devices. The main drawback is that such devices cannot be used for high temperatures and pressures. Another restriction is that the use of substances that may dissolve the device made of wax should be avoided to retain the integrity of the device.
What difficulties did you face in developing this method?
Kazarian: Programming of a commercial system for printing specific microfluidic devices was not straightforward (code had to be written by hand) but we have now introduced a new approach that can take any drawing and convert it to the required machine code, speeding up development and prototyping of new devices.
What are your plans for future research with the FT-IR imaging technique?
Kazarian: There are many avenues that we would like to explore. Our research interests are diverse, encompassing studies of chemical reactions, live cells, and other biological systems. We are obtaining truly exciting results in these areas already, and expect that these developments would advance this methodology for emerging applications.
Related content: Dr. Kazarian’s article in Spectroscopy can be accessed at http://www.spectroscopyonline.com/Kazarian