Chalcogenide glasses are a matchless material as far as mid-infrared (IR) applications are concerned. They transmit light typically from 2 to 12 μm and even as far as 20 μm depending on their composition, and numerous glass compositions can be designed for optical fibers. One of the most promising applications of these fibers consists in implementing fiber evanescent wave spectroscopy, which enables detection of the mid-IR signature of most biomolecules. The principles of fiber evanescent wave spectroscopy are recalled together with the benefit of using selenide glass to carry out this spectroscopy. Then, two large-scale studies in recent years in medicine and food safety are exposed. To conclude, the future strategy is presented. It focuses on the development of rare earth-doped fibers used as mid-IR sources on one hand and tellurium-based glasses to shift the limit of detection toward longer wavelength on the other hand.
Fiber evanescent wave spectroscopy (FEWS) explores the mid-infrared domain, providing information on functional chemical groups represented in the sample. Our goal is to evaluate whether spectral fingerprints obtained by FEWS might orientate clinical diagnosis. Serum samples from normal volunteers and from four groups of patients with metabolic abnormalities are analyzed by FEWS. These groups consist of iron overloaded genetic hemochromatosis (GH), iron depleted GH, cirrhosis, and dysmetabolic hepatosiderosis (DYSH). A partial least squares (PLS) logistic method is used in a training group to create a classification algorithm, thereafter applied to a test group. Patients with cirrhosis or DYSH, two groups exhibiting important metabolic disturbances, are clearly discriminated from control groups with AUROC values of 0.94±0.05 and 0.90±0.06, and sensibility/specificity of 86/84% and 87/87%, respectively. When pooling all groups, the PLS method contributes to discriminate controls, cirrhotic, and dysmetabolic patients. Our data demonstrate that metabolic profiling using infrared FEWS is a possible way to investigate metabolic alterations in patients.
Due to remarkable properties of the chalcogenide glasses, especially sulphide glasses, amorphous chalcogenide films
should play a motivating role in the development of integrated planar optical circuits and their components. This paper
describes the fabrication and properties of optical waveguides of pure and rare earth doped sulphide glass films prepared
by two complementary techniques: RF magnetron sputtering and pulsed laser deposition (PLD). The deposition
parameters were adjusted to obtain, from sulphide glass targets with a careful control of their purity, layers with
appropriate compositional, morphological, structural characteristics and optical properties. These films have been
characterized by micro-Raman spectroscopy, atomic force microscopy (AFM), X-ray diffraction technique (XRD) and
scanning electron microscopy (SEM) coupled with energy dispersive X-ray measurements (EDX). Their optical
properties were measured thanks to m-lines prism coupling and near field methods. Rib waveguides were produced by
dry etching under CF<sub>4</sub>, CHF<sub>3</sub> and SF<sub>6</sub> atmosphere. The photo-luminescence of rare earth doped GeGaSbS films were
clearly observed in the n-IR spectral domain and the study of their decay lifetime will be presented. First tests were
carried out to functionalise the films with the aim of using them as sensor.
Chalcogenide glass optical fibers possess very low optical losses in the middle infrared range from 2 to 12 mm. They were used to implement remote infrared spectroscopy, known as Fiber Evanescent Wave
Spectroscopy (FEWS). Due to their hydrophobic behavior, such sensor is especially suitable for application in biology and medicine where water is a nuisance to detect relevant information. Moreover, the design of the sensor using tapered fibers enables to improve the signal to noise ratio. Then, once coupled with unsupervised analysis technique such as Principle Component Analysis (PCA), it has been shown that this tool is efficient to differentiate between obese and control mice by recording their serum FEWS spectra. The same method has been carried out to detect in situ the both phenotypes of a bacterial culture.