Figure 9. a) Representative Raman spectra rich in specific aortic components. b) Representative Raman mapping images, associated histology, and immunofluorescence.[135] Copyright 2017, American Association for the Advancement of Science.
Urinary calculi
The formation of urinary calculi is a pathological biomineralization process that may be induced by endogenous or exogenous factors. Such as gender, genetics, diet, water intake, and occupation.[205] Among the types of urinary calculi are calcium oxalate dihydrate (COD), magnesium ammonium phosphate hexahydrate (MAPH), calcium oxalate monohydrate (COM), and calcium hydrogen phosphate dihydrate (CHPD), Penta-calcium hydroxy-triphosphate (PCHT), and uric acid (UA).[207] Proteins in urinary stones cannot be detected by Raman spectroscopy due to their fluorescence background. However, carbonate and calcium oxalate, which account for less than 5% of the total stones, can be detected.[246] The COD spectrum shows O-H stretching vibration at 3264-1, and the C=O vibration and C-O symmetric stretching lead to a clear band change.[8,63,247] The Raman spectra of COM showed that the presence of weaker peaks at 1631 cm-1 is caused by C-O asymmetric stretching, and the peak at 896 cm-1 is caused by C-C stretching. 502 cm-1, 1462 cm-1, and 1473 cm-1 peaks are caused by O-C-O surface bending.[8,138,208,248] The Raman spectrum of MAPH is dominated by the P-O vibration peak, with an obvious peak at about 950 cm-1.[249] The weak peak at 431 cm-1 is due to the phosphate band in magnesium ammonium phosphate (guano stone). The vibration peak at 584 cm-1 is caused by the O-P-O symmetric bending mode.
The minerals of urinary stones are different, resulting in differences in the characteristic peaks of the Raman spectra, which is the main basis on which Raman spectra can be effectively analyzed and classified. Raman spectroscopy and laser-induced breakdown spectroscopy (LIBS) were combined to evaluate the chemical composition of different classes of urinary stones. LIBS explores elemental features that complement the molecular details of the samples and improve the accuracy of the analytical results of urinary stones.[250]Tip-enhanced Raman spectroscopy (TERS) was used to enhance the characteristic peaks of proteins in urinary stones, providing information on the surface specificity of the phosphoprotein osteopontin (OPN) adsorption on the surface of COM crystals (Figure 10 ).[251] It was revealed that competition and inhibition of COM formation by OPN plays a key role in COM formation during ectopic biomineralization of calcium oxalate kidney stones.[251] Although there are significant differences in urinary calculi, which can provide effective classification information, the causes of urinary calculi need to be further studied. This is a prerequisite for providing a prognosis after the diagnosis of urinary calculi.