Sub-millimetre flexible fibre probe for background and fluorescence free Raman spectroscopy

Stephanos Yerolatsitis,Tom Quinn,Kevin Dhaliwal,Keith Finlayson,Harry Wood,Ahsan Akram,Katjana Ehrlich,András Kufcsák,Robert Thomson,James Stone,Susan Fernandes

doi:10.1117/12.2577595

Abstract

We have developed a compact background and fluorescence free endoscopic Raman probe using shifted-excitation Raman difference spectroscopy (SERDS) with an optical fibre featuring a negative curvature excitation core and a coaxial ring of multimode collection cores. The probe consists of a single optical fibre with an outer diameter below 0.25 mm packaged in sub-millimetre tubing making it compatible with the working channels of standard endoscopic tools. The light in the fibre is guided in air and therefore interacts little with silica, enabling an almost background-free transmission of the excitation light and collection using a single optical fibre. In addition, we used the SERDS technique and a tunable 785 nm laser to separate the fluorescence and the Raman spectrum from highly fluorescence samples, demonstrating the suitability of the probe for biomedical applications.

Highlights

Raman spectroscopy is a label-free, non-invasive and nondestructive method for examining unknown samples and obtaining useful information regarding their biochemical composition
We have developed a submillimetre flexible fibre-optic Raman probe for endoscopic use by incorporating a single optical fibre featuring a negative curvature excitation core and a coaxial ring of collection cores packaged in sub-millimetre biocompatible polyimide tubing
We previously demonstrated that such fibres can minimise the generated silica background and enable an almost silica background free collection of the spectrum from the distal sample using a single fibre and no distal optics [2]

Summary

Introduction

Raman spectroscopy is a label-free, non-invasive and nondestructive method for examining unknown samples and obtaining useful information regarding their biochemical composition. The use of Raman spectroscopy as a clinical invivo tool has not yet been fully realised due to various technical challenges [1] One such challenge is the silica background generated from the optical fibres used to remotely examine otherwise unreachable tissue regions [2]. Most of these probes consist of either separate fibre cores for excitation and collection or microstructure fibres and bespoke distal optics [46] This increases the outer diameter, decreases the flexibility of the probe and limits their use to characterise tissue which requires probe miniaturisation for access. While the silica background is minimised in the collected signal through the use of the NCF, fluorescence from the distal sample still introduces a significant challenge in detecting Raman signals from weak Raman scatterers, such as biological tissues. It was previously shown that SERDS can eliminate fluorescence more effectively compared to many numerical and baseline fitting methods [9]

Methods

Results

Conclusion