When laser spectroscopy is combined with microscopy, spatial variations of the chemical compositions of both organic and inorganic samples can be precisely determined. One of the spectroscopic microscopy techniques used in our laboratory is confocal Raman spectroscopy. It is a label-free method that gives information of the rotational-vibrational spectroscopic signatures of the material under study. Together with our collaborators, we use confocal Raman spectroscopy in a wide range of applications, including material sciences and research of plasmonic catalysis, biomedicine and pharmacy. One of the commercial Raman instruments in our lab (NT-MDT NTEGRA Spectra II) has imagining modalities complementary to confocal Raman. A modality worth special mention is Tip-Enhanced Raman Spectroscopy (TERS). In TERS, the Raman pump laser beam is focused onto the apex of a sharp metal tip. The strong localization of the laser field at the tip apex leads to a Raman signal enhancement and improves the spatial resolution significantly below the diffraction limit, down to the nanometer scale.
One of the remaining challenges with optical spectroscopic microscopy is the generally modest imaging speed. This is an issue especially in biomedical applications, where live cell samples and time-dependent phenomena are often studied. We are currently developing a multiplex coherent Raman microscope, which targets significant enhancement of the imaging speed and signal-to-noise ratio. The work is done as part of the qCSI (Quantitative Chemically-Specific Imaging Infrastructure for Material and Life Sciences) consortium, which is funded by the Academy of Finland and led by Prof. Clare Strachan (Faculty of Pharmacy, Helsinki). For more information about qCSI, see http://qcsi.fi.