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.