This article is based around a talk given by Malgorzata Jedrzejewska-Szczerska, from the Gdansk University of Technology, Poland, at the NANOMED conference hosted by the NANOSMAT Society in Manchester on the 26-28th June 2018. In her talk, Malgorzata talks about how different nanomaterials can be used in optical fiber sensors medical applications.
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In today’s era of interdisciplinary research, there are converging areas where medical applications and the use of optoelectronics meet. Some prime examples of these areas are diagnostics using absorption and Raman spectroscopy and topographic optical microscopy.
There is also an emerging area of using individual sensors that can be used directly by a patient at the point of care. These sensors currently require more collaborative efforts to realize these applications clinically, but fiber optical sensors show the most promise. One of the main reasons for fiber optics being the most promising is because they are not prone to electromagnetic interferences (such as electrical impulses from the heart), there is no risk of electrical sparks as they are dielectric, chemically passive and biocompatible, and have a multiplexing capability.
Malgorzata talked about how her research group is using nanomaterials in three different ways in these type of sensors – in the sensing medium (most common), as a material to tune the meteorological properties of the sensors and as protective layers. Her talk at the conference focused on the first two.
The group attached different nanolayers to the end of fiber optics to construct a simple two-beam interferometer that measures the phase differences between the two beams. The critical aspect of these end sections is that the refractive index of the nanomaterial needs to change when there is a localized temperature change.
One application example of their fiber optic sensors is a 6 nm zinc selenide nanolayer as a sensing medium to detect changes in temperature. These nanolayers are combined with a broadband optical spectrum analyzer, temperature calibrators, and fiber optic devices and can be used to determine if a temperature change has happened through a shift in the spectra.
Other materials have been used as a sensing medium, such as zinc oxide, but with more significant challenges because the diameter of the zinc oxide layers is 200 nm. Despite this, and the subsequent smaller heat measurement, the group still observed a shift in the spectra.
Moving on to materials that can tune the meteorological properties of sensors, the research group have used nanolayered materials to create an interferometer at the boundary between the optical fiber and the interferometric cavity. By simply changing the optical properties of the mirrors and the fiber optic tip, the team can increase the visibility of a measurement signal. In this approach, the team has used different types of nanolayered materials (with different thicknesses) to tune the contrast of the meteorological parameters, especially at the fringes of the spectra, and increase visibility within the spectra.
Another approach has involved the use of zinc oxide in the tip to measure the refractive index of liquids. This has resulted in an increased measurement range for many liquids, and especially for those who have a refractive index similar to that of fiber optic glass. The researchers have also used titanium dioxide to construct fiber-optic interferometers with small cavities (smaller than zinc oxide and half the size of other optical fiber sensors), and this enables smaller samples to be measured.
Overall, the use of nanomaterials gives researchers more options in the field of bio-optical sensing. One application area of interest could be in neural sensing, but to do this, more research is going to be needed to make them more biocompatible if they are to be used in a clinical setting.
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