Several tools for Raman analysis have been produced and already tested for blood glucose monitoring in vivo that plays a crucial role in people suffering from diabetes. Raman spectroscopy in reflection geometry allows collecting signals from the forearm applying a paraboloidal mirror combined with a spectrograph and a tall detector.
Nevertheless, Raman fiber optic probes have unwanted Rayleigh light reflected from the tissue surface. Thus, the researchers employ a transmission Raman spectroscopy tool with a nonimaging optical fiber element. Recently fiber optic probe for Raman analysis was applied. Raman fiber optic probe enables them to reliably measure the signal from the same tissue spot under the room light.
Nonetheless, “the focused radiance of laser from one excitation fiber limits the sampling volume, and a small tip of the Raman probe presses the skin over hours of measurement, which might prevent glucose-containing ISF from circulating across the sampling volume”. Usually, a pressure mark on soft samples is distinguished after utilizing this type of fiber probe.
The main purpose of this research is considered to be the determination of glucose fingerprint peaks in vivo transcutaneous Raman analysis. The promising application of fiber optic probe includes not only the determination of glucose fingerprint peaks but also the study of their linear changes with the related glucose levels that can overcome the challenge of the long-standing ambiguity about whether Raman spectroscopy can detect glucose signal in transcutaneous glucose sensing.
It is possible to perform due to the illumination collection geometry to manage the sampling volume applying the noncontact off-axis system. It should be noted that such a fiber optic system makes the instability of the Raman probe lower by illuminating a relatively large tissue under custom-designed large collection fiber optic bundles.
To be more precise, the off-axis illumination and vertical collection geometry take away the specular Rayleigh reflection from the skin surface, therefore, it allows reducing the burden of the Rayleigh rejection filter at the fiber probe tip. Moreover, the non-contact sensing offers such an advantage as freedom from potential distortions of tissue that is crucial for reliable long-term measurement.
The Raman fiber optic probe consists of an 830-nm diode laser, an imaging spectrograph, and a charge-coupled device. The operating principle is based on a filtered laser beam of 250 mW that is focused on the ear skin resulting in an elliptical beam of 1 mm × 2 mm. Herewith, the laser beam emission from the sensing spot of the skin surface is compiled by a custom-made, round-to-linear fiber optic bundle comprising of 61 optical fibers.
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