Raman spectroscopy of bio fluids: an exploratory study for oral cancer detection

Methods in Raman spectroscopy for saliva studies – a review

“…[208] However, it is not clear within most Raman studies how saliva may be different for participants who arrived at the point of sample deposition by different levels of exertion i.e., a range of more modest activity levels. 1-6 hours [83,131,140,189,190,193,207,215,216] Overnight [98,202,[217][218][219][220] Mouth Wash (water) Immediately prior [97,98,202,217,218,[220][221][222][223][224][225][226][227] <1 hour [60,96,99,100,193,213,215,228] Mouth Wash (other) (alcohol-free) [125,200,201,229] Saliva type Unstimulated [47,50,60,83,96-100,103,125,131,138,140,190,193,200,204 , 213-217,219-221,223-227,229-231] Stimulated [69,146,189,207,…”

“…A dimensionality reduction step may be further employed to reduce the computational load before a subsequent classification algorithm is applied. Often used in Raman-saliva studies is the unsupervised Principal Component Analysis (PCA) method, [83,97,98,215,221,223,227,244,360] which separates unknown spectra by redefining the co-ordinate system to maximize the variation. Dies et al, [244] for instance, employ PCA to discriminate between different drugs in water and subsequently, spiked cocaine in saliva (Figure 4C).…”

“…Spectral features can be compared with statistical methods, primarily, hypothesis p-value testing for singular variables. The Student's t-test [153,215,217,219,225,227] and (Wilcoxon-)Mann-Whitney U test [125,200,222] have been used to study specific peaks or validate multivariate outputs. This analysis of singular variables allows for a strong depiction of the statistical relevance of a spectral feature adding to the data interpretation.…”

“…Test-training separations of 80%/20% [83,125,132,239,369] are apparent in Raman-saliva studies, however, Raman studies on saliva have also been performed with 90%/10% [204] and 60%/40% splits. [362] Within chemometric-focused Raman-saliva studies, there is a range of sample sizes used varying from 20 samples (10 healthy/10 unhealthy) [96,103,215] to 128 (64 healthy/64 unhealthy) samples in total. [132,238,360,369] Healthy/unhealthy patient splits usually are approximately equal.…”