With the pandemic, we've all become more familiar with medical equipment we didn't know before: infrared thermometers, UV sterilizers, and more. Among these, the use of a luminous plastic clip around the finger has become increasingly common. This clip is an oximeter that calculates the level of oxygen in the blood. But how exactly does it work? What is the technology that allows this measurement and what other things can it do?
Photonics is a science belonging to optics that studies light and the propagation of photons through translucent bodies. The human body is translucent, that is, it does not block or reflect light. This means that part of the light is able to pass through the skin, muscles and blood vessels and exit the other side. This simple property was then used for the internal exploration of the bodies without any kind of invasion.
Returning to the oximeter example, this is capable of measuring the ratio between oxygenated and non-oxygenated hemoglobin thanks to a red LED light located on one side of the clip and a light detector located on the other side. When the LED light passes through the finger it encounters the hemoglobin in the blood. Now, non-oxygenated hemoglobin absorbs red light to a greater extent than oxygenated one. The amount of light that is able to pass through the finger therefore depends on the proportion between these two types of hemoglobin. In this sense, different wavelengths can be used, such as infrared, which are just below those of the visible colors. The absorption efficiency of molecules, including hemoglobin, varies with the variation of the wavelength of light. For this reason, comparing the absorption of visible light with infrared can provide a more accurate estimate.
The emerging sensor industry is studying new and increasingly precise and less invasive estimation methods, not only to calculate blood saturation but also for blood vessel mapping and tumor profiling. The great innovation of the use of photonics in the field of medicine lies precisely in the capacity of inference, that is the possibility of being able to use a simple sample of saliva or sweat for the diagnosis of certain diseases. Human saliva, in particular, mirrors the composition of hormones and proteins in the body and can signal early on the presence of certain types of cancers and infectious or autoimmune diseases, including prostate cancer, sarcoidosis and a whole host of viral infections. The exploration of our translucent body through pulses of light is another possibility; the pulses of light, similar to flashes, are projected onto a specific area. When they reach a body, these impulses act like percussion; striking the molecules of the cells make them vibrate, these vibrations are recorded and then compared with the vibrations produced by other materials (each material has its own vibration frequency). This study is precise and non-invasive and allows to obtain the chemical composition of a tissue and understand whether the tissue is healthy or not.
Compared to other methods, the applications of photonics have the advantage of using 'photonic tracks'. As with electricity, which requires a conductor cable to pass electrons, the photonic tracks are optical fibers for the transport of photons. Photons travel at the same speed of light and given the absence of mass of photons compared to electrons, their transport does not involve the dispersion of heat, resulting in savings in terms of time and energy.
Photonics is not only innovating in the medical sector but also in numerous other areas. In computer science, traditional processors, chips containing countless electrical tracks on which electrons run, could be replaced by photonic processors simply by replacing electrons with photons (and reducing the risk of the computer overheating). In agriculture, photonics is used to monitor the state of the land or to harvest food at the peak of its nutritional power. This is possible thanks to the study of light in the moment immediately following the impact with the obstacle it encounters; when a light beam hits an object, part of it is absorbed and part is reflected. By studying the reflected part at different frequencies, it is possible to collect information on the chemical (degree of hydration, amount of sugars and amino acids) and physical characteristics of the object. In the automotive industry, light is used as a sensor to see through the fog or around the car (very similar to the radar technology of bats and ships, but the reflection of light is used instead of sound).
In conclusion, photonics promises to be at the center of the new innovations of the near future, both in the technological, medical, agricultural and industrial fields. The main countries that are now carrying out research in this direction are China and Europe. An economic value is expected to be around 405 billion dollars and a growth in jobs of around 20 thousand per year.
Translated by Veronica Giustiniani