Role of Raman spectroscopy and surface enhanced Raman spectroscopy in colorectal cancer

Table 1 A comparison of Raman spectroscopy, fourier transform infrared spectroscopy and hematoxylin and eosin staining strengths and weaknesses

	Raman spectroscopy	FTIR	Hematoxylin and eosin staining
Method of detection	Inelastic scattering of monochromatic (laser) light	Absorbance (polychromatic light source)	Combination of basic and acidic dyes
Real time	Yes	Yes	No
Wavenumber range (cm-1)	50-4000	400-4000	N/A
Spatial resolution	1 μm	5 μm	Cellular
Enhancement techniques	SERS, TERS, CARS, SORS, SRS	ATR	"Special" staining
Effect of water	Minimal	Large absorbance in NIR region	No
Destructive to sample	No	No	Yes

SERS: Surface enhanced Raman spectroscopy; TERS: Tip enhanced Raman spectroscopy; CARS: Coherent anti-Stokes Raman spectroscopy; SORS: Spatially offset Raman spectroscopy; SRS: Stimulated Raman spectroscopy; ATR: Attenuated total reflection; FTIR: Fourier transform infrared spectroscopy; NIR: Near-infrared; N/A: Not available.

Table 2 A summary of the different clinical applications of Raman spectroscopy to colorectal cancer

Method	Sampling type	Sample number	Ref.	Year	Spectral region (cm-1)	Laser excitation (nm)	Data analysis
Probe	In vivo (tissue)	20	Shim et al[42]	2000	450-1800	785	PCA, PLS, ANN
Probe	In vivo and ex vivo (tissue)	9	Molckovsky et al[44]	2003	900-1800	785	PCA, LDA, LOOCV
Micro-spectrometer	In vitro (primary tissue)	10	Chen et al[38]	2006	500-1900	782.5	PCA
Probe	Ex vivo (tissue)	59	Widjaja et al[45]	2008	800-1800	785	PCA, SVM, LOOCV
Micro-spectrometer	Ex vivo (tissue)	54	Beljebbar et al[47]	2009	600-1800	785	SVM, PCA
Micro-spectrometer	In vitro (serum)	120	Li et al[37]	2012	800-1800	785	PCR, PLSR, LDA
Micro-spectrometer	In vitro (cell lines)	N/A	Ranc et al[39]	2013	400-1800	532	PCA
Probe	In vitro (tissue)	177	Wood et al[43]	2014	800-1800	830	PCA, LDA, LOOCV
Micro-spectrometer	In vivo (tissue)	50	Bergholt et al[78]	2014	800-1800 and 2900-3600	785	PLS, LDA

PCA: Principle component analysis; LDA: Linear differential analysis; PLS/PLSR: Principle least squares regression analysis; LOOCV: Leave one out cross validation; ANN: Artificial neural network; SVM: Support vector machine; PCR: Principle component regression.