Enhanced Ultraviolet Spectroscopy by Optical Clearing for Biomedical Applications

Lipofuscin-Type Pigment as a Marker of Colorectal Cancer

“…Current optical diagnostic and therapeutic methods work at wavelengths within the traditional tissue windows: I (625-975 nm), II (1100-1350 nm), III (1600-1870 nm), and IV (2100-2300 nm) [3,4]. Complementary to these wavelength ranges, where light penetration depth presents local maxima for natural tissues [2,5], the use of optical clearing treatments can induce other optical diagnostic and treatment windows, as it was recently demonstrated for the ultraviolet (UV) range with transmittance efficiency peaks at (230 ± 30), (275 ± 25 nm), and (300 ± 40 nm) [6,7].…”

Tissue Spectroscopy and Optical Clearing of Colorectal Mucosa in the Pursuit of New Cancer Diagnostic Approaches

“…These studies showed that the clearing potential of an OCA is related to its protein dissociation capability, proving that the protein dissociation is also an OC mechanism [47][48][49][50]. More recently, other studies have showed that this mechanism also occurs in other tissues such as colorectal muscle [25], or colorectal mucosa [29]. In the first of these studies it was demonstrated that the protein dissociation increases in magnitude with the osmolarity of glycerol in the treating solution [25].…”

“…Such transient effect allows to reach deeper light probing depths through the partial replacement of tissue water by a harmless agent, designated as optical clearing agent (OCA) [21]. These OCAs have a higher refractive index (RI) than water, better matched to the RI of the other tissue components, which are commonly designated as tissue scatterers [21,28,29]. Due to heterogeneous composition of biological tissues, the various biological components such as protein fibers and globules, lipid droplets, phospholipid membranes, cells and their organelles, like mitochondria and nucleus, are surrounded by the tissue fluids, e.g., the interstitial fluid (ISF) or cell cytoplasm [30].…”

“…Such water maintains the hydration of those biological components in the tissues and provide nutrients to the cells, but it can also be converted into mobile water and flow out if the osmotic pressure of the OCA is maintained for several hours or days [21]. As a result of the fast loss of mobile water in the first few minutes of treatment, sample thickness decreases, leading to the close approximation of the tissue scatterers [21,29,39]. A more compact and better organized packing of tissue scatterers is created…”

“…In the first of these studies it was demonstrated that the protein dissociation increases in magnitude with the osmolarity of glycerol in the treating solution [25]. In the later study [29], Carneiro et al demonstrated that the protein dissociation rate can be discriminated in healthy and pathological colorectal mucosa for the same high glycerol osmolarity in the treating solution. Such result of discriminated protein dissociation rates in healthy and cancer tissues is to be expected due to the higher protein contents that cancer tissues are known to have [51].…”