Raman spectra were recorded on an Edinburgh Instruments RM5 Confocal Raman Microscope equipped with 532 nm and 785 nm lasers and a back-illuminated charge-coupled device detector. The samples were prepared by depositing ∼10 mg of dry MPs onto stainless steel slides and were viewed with episcopic illumination in dark-field mode. The µ-Raman was aimed at separate regions of individual MPs, as well as at different MPs, and spectra were taken over a range of time-scales and intensities until clear signals could be obtained. The spectra were processed (baseline correction and smoothing) using Edinburgh Instruments Ramacle software, as well as MestreNova.