Fibre optic probe

Tsai D P, Othonos A, Moskovits M and Uttamchandani D 1994 Raman spectroscopy using a fibre optic probe with subwavelength aperture Appl. Phys. Lett. 64 1768... 

A variety of optical systems have been described which use optical fibres to perform remote Raman spectroscopic analyses. These are of particular value when the sample has to be observed under hostile or hazardous environmental conditions, such as the in-line monitoring of chemical production. The collection radius of such fibre-optic probes is of the order 100 pm. 

The basic layout of Raman sensors is similar to fluorescence probes. The common sensor form is that of a fibre optic probe, with excitation and collection fibres. As the excitation light comes from a monochromatic source no excitation filter is required, but a spectrally matched emission notch filter blocking the excitation wavelength is almost always part of the sensor head. 

M. Blanco, J. Coello, H. Iturriaga, S. Maspoch, C. Pezuela and E. Russo, Control analysis of a pharmaceutical preparation by near-infrared reflectance spectroscopy a comparative study of a spinning module and fibre optic probe, Anal. Chim. Acta, 298, 183-191 (1994). 

Reeves, J.B. Ill and McCarty, G.W. (2001) Quantitative analysis of agricultural soils using near infrared reflectance spectroscopy and a fibre-optic probe. Journal of Near Infrared Spectroscopy 9, 25-34. 

Gonzalez-Martin, I., Hemandez-Hierro, J. M., Vivar-Quintana, A., Revilla, I., and Gonzalez-Perez, C. (2009). The application of near infrared spectroscopy technology and a remote reflectance fibre-optic probe for the determination of peptides in cheeses (cow s, ewe s, and goa t s) with different ripening times. Food Chem. 114,1564—1569. 

Schwartz et al. evaluated the use of fibre-optic probe dispersive Raman and PLS calibration to study crystallisation in a hanging drop experiment. They could show that the lysosome concentration could be monitored during the experiment through the concentration phase, nucleation and crystal growth [27], In later experiments, they were able to utilise in-line Raman data to control the concentration of lysozyme to affect the crystallisation path and thereby obtaining the desired large single crystals [28], The same setup was used for crystallisation of apoprotein. Also in this case the Raman data were used to control the evaporation and thus the supersaturation for optimised crystal size [29]. 

The evolution of lasers and detectors has enabled Raman spectra of high signal-to-noise ratio to be acquired in shorter time frames with lower laser powers, thus opening up new possibilities for Raman spectroscopic analysis of biological samples. Some applications have evolved to the point that it is no longer necessary to excise out the sample and bring it to the spectrometer for analysis. Rather, with fibre-optic probe technology, it is now possible... 

The initial studies described above were conducted on Raman microspectrometers on extracted human teeth. In order to translate this research from the laboratory bench to the dental chair side, the next step it is to develop dedicated systems for clinical use. A key element to this development is the use of fibre-optic probes to allow measurements in vivo. We recently reported a study in which optical fibres were used for PRS measurements [48], Although not yet fully realized into a dental probe, this study demonstrated the design and feasibility of acquiring parallel- and cross-polarized Raman spectra via a bifurcated optical fibre whose distal terminal has the two fibres aligned vertically for simultaneously collecting spectra from the two polarization channels on a 2D CCD array. Simultaneous data acquisition will allow for more rapid measurement times in vivo. 

At-line sampling may involve a flow-through cell in the NIR spectrometer in one process a glass-lined steel reaction vessel was used in combination with a fibre optic probe for measurements in a full scale chemical plant reactor [57]. Fibre optic bundles can be used to transmit NIR radiation to the reaction matrix and take signal back to the spectrometer. NIR is notoriously sensitive to changes in temperature and methods for keeping the temperature constant must be incorporated into the instrumentation. 

Figure 8.11. Portable Raman spectrometer coupled to an acoustic levitator. A — Dantec ultrasonic acoustic levitation device, B — Raman fIbre-optIc probe, C — control unit for the acoustic levitation device, D — quartz halogen light source and E — InPhotonIcs portable 785-nm Raman spectrometer. (Reproduced with permission of the American Chemical Society, Ref [120].)...

Figure 3.44. A fibre-optic probe with air cooling and a sapphire window suitable for use in a reactive extruder or other rugged environment. After Hansen and Khettry (1994).

Figure 9.11 Schematic diagram of a spectrometer coupled via a fibre optic probe to a process stream for on-line analysis.

Hypoxia can now be detected and quantified by microelectrodes and the binding of reactive, reduced metabolites of nitroimidazoles, which reflect oxygen levels (because the radical-anion reduction intermediate is oxygen reactive) [30]. A new fibre-optic probe for tissue oxygenation, now available commercially, relies on measurements of emission from a ruthenium probe, which has an oxygen-dependent excited-state lifetime [31]. Acute or fluctuating hypoxia, which has features in common with ischaemia/reperfusion and therefore with myocardial infarction and stroke, can be detected by vascular stains such as bisbenzimidazole intercalators with different fluorescent characteristics. These can be administered intravenously a few minutes apart ... 

The availability of Raman spectrometers with fibre optic probes facilitates coupling with other analytical instruments. The use of Raman spectroscopy coupled with DSC and variable temperature/humidity X-ray powder diffraction [88] has been demonstrated. 

Effective Reaction Monitoring of intermediates by ATR-iR Spectroscopy Utiiizing Fibre Optic Probes... 

Additionally, ATR-based mid-IR fibre optic probes represent an entirely non-invasive technique, which has recently been shown to be a promising tool e.g. for biotechnological applications (Mazarevica, 2004) and, even more impressively, for obtaining spectroscopic information in vivo (Brancaleon et al., 2000). 

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