“…PTI has been shown advantageous for a range of different biomaterial/bio-tissue based studies including in vivo imaging in C. Elegans [189], imaging of cellular dynamics for living neurons and oligodendrocytes [211], ultrafast chemical imaging [193,212], label-free PTI of fixed mouse melanoma [27], label-free in-vivo imaging of cellular organelles, such as the mitochondria, and heme proteins such as haemoglobin and cytochromes [202,213], PTI atomic force microscopies (AFM-IR) for studying eukaryotic cells [214], and selectively targeting molecular bonds for identification of cellular membranes [29]. However, some common limitations for PTI studies on tissues, especially quantitative biochemical PTI studies, include: the overlap of the water signal in the mid-IR region often resulting in low signal to noise values [189,215], and heat-induced photo-chemical reactions, which do not produce heat but rather may produce a new chemical species which may alter the photothermal properties of the sample [185].…”