**3. Concluding remarks and challenges**

As shown, the reliability as well as the kind and amount of molecular information can be improved by extending a Raman analysis to include polarization resolved experiments. For example in the studies of DSCs in [33] the spectral distribution of the strongest Raman bands in fresh and aged DSCs was found to be practically identical, while significant changes of the DPR ratios were observed in [32]. Thus, the conclusions about dye stability become more reliable, when the polarization is measured. Furthermore, the possibility for studying the adsorptiondesorption at the Dye-TiO2 interface seems promising. The polarized RBC study demonstrated that aggregation between the haem molecules inside the RBCs can be studied *in vivo*, which, e.g. opens for the possibility of monitoring the effects of drugs added to the blood. Recently, Jernshøj et al. applied a combination of dynamic light-scattering and polarization resolved RRS to study, among other things, the aggregation versus pH of Arenicola Marina extracellular haemoglobin (a giant molecule with mass ~**3.6 10**<sup>6</sup> **Da** and 144 oxygen binding sites) [30]. This study demonstrates the high applicability of polarized resolved RRS with respect to extracting rather detailed information about molecular systems involving very large molecules.

Finally, three challenges that one has to face when applying polarization resolved RRS should be mentioned:


Since CCD-cameras are applied in Raman microscopes, it is in fact possible through a modification of the collection optics to monitor the parallel and perpendicular polarized spectra simultaneously. This has three important implications: the accuracy of the measured DPR is improved, since modifications of the sample induced by the laser appear in both signals, the S/N ratio can be increased through averaging a large amount of spectra and most importantly it open for performing polarized resolved Raman imaging.
