Effects of laser excitation wavelength and optical mode on Raman spectra of human fresh colon, pancreas, and prostate tissues

Abstract

Early cancer detection is the central and most important factor for allowing successful treatment and resultant positive long‐term patient outcomes. Recently, optical techniques have been applied to this purpose, although each has inherent limitations. In particular, Raman spectroscopy applied in the pathological diagnosis of cancerous tissues has received increasing attention, with the merit of being highly sensitive to the biochemical alterations in tissue compositions and applicable in vivo. Nevertheless, its application has been impeded by the high background intensity, which masks the Raman signal of biological molecules. In this work, the influence of laser excitation wavelength (785 vs. 830 nm) and optical mode (single mode vs. multimode) on the background intensity of fresh human tissues was studied. Based on the results, laser with 830 nm excitation demonstrated better background reduction than that with 785 nm excitation for the same optical mode, but the Raman signal intensity was conversely reduced, and the signal‐to‐noise ratio (SNR) not improved. In contrast, by comparing single‐mode and multimode 785 nm excitations, it was shown that the single‐mode laser with its smaller beam waist and beam propagation factor had better background reduction ability and an improvement of the SNRs. It is speculated that this decrease in background intensity comes from the effect of the optical mode on the Mie scattering from the biological tissue. High‐quality spectra based on a careful selection of both laser excitation wavelength and optical mode will benefit Raman measurements in further research focusing on spectral interpretation and histopathological correlation ultimately aimed toward intraoperative applications. Copyright © 2014 John Wiley & Sons, Ltd.

In Vivo Fiber Optic Raman Spectroscopy of Muscle in Preclinical Models of Amyotrophic Lateral Sclerosis and Duchenne Muscular Dystrophy

“…The design was based on that presented by Day and Stone and is shown schematically in Figure . A 830 nm semiconductor laser (Innovative Photonics Solutions) was used to provide a superior signal/noise ratio due to lower background fluorescence than shorter wavelength excitation. , In line filters were placed approximately 15 cm from the probe tip to reduce the effect of Raman and fluorescence generated in the delivery fibers. These comprised a bandpass filter on the excitation delivery fiber and a long-pass filter on the collection fiber (Semrock Inc.).…”

Exploring the effect of laser excitation wavelength on signal recovery with deep tissue transmission Raman spectroscopy

“…The influence of excitation laser wavelength on the Raman signal it is well known in the scientific community and documented. [43][44][45] In reality the spectra are influenced not only by the laser wavelengths used, but also the transmission profile of the intermediary optics and diffraction grating, as well as the quantum efficiency of the CCD detector. The spectral region for Raman detection ranges from 834 nm to 960 nm depending on the laser wavelength and the Raman bands are located on the descending slope of the quantum efficiency curve of the CCD detector.…”

Optimal choice of sample substrate and laser wavelength for Raman spectroscopic analysis of biological specimen

“…In terms of source wavelength, 785 nm spectra had a lower background intensity than that at 830 nm, and it was found that the SNR was 1.2-1.6 times higher for 785 nm MM than that recorded from the 830 nm MM. 23 Therefore, taking this into consideration, all measurements in this study are based on a SM source.…”

“…This graph is based on eqn (5), and therefore is dependent on the assumptions that were made in its derivation; a wavelength bandwidth of 150 nm is assumed. The effect of the source optical mode for Raman spectroscopic measurement of human tissues has previously been analysed by Li et al (2014), 23 whereby the inuence of singlemode (SM) and multi-mode (MM) source lasers at 785 nm and 830 nm were compared in terms of the background signal intensity generated by tissue autouorescence and the Raman signal intensity measured from human tissue samples. Overall, a reduction in background, increase in SNR and a reduction in Mie scattering was found for 785 nm SM when compared to 785 nm MM.…”