As pointed out in the previous sections, the mortality of Sars-CoV-2 and related virus rapidly increases when the temperature goes over 39 °C. This effect is accompanied by a reduction of the antibodies production, which is one of the major causes of death. On the other hand, it is also well known that human organs can support for short times temperature over 40 °C. The weakest organ is the brain. Its damage temperature is 42 °C where other organs can reach 45 °C for a limited time. Thus, to heat up the human body with a microwave beam to temperature lower than 45 °C for a period up to some tens of minutes, might turn beneficial. Although it is presumable that this approach does not completely eliminate the virus population, a strong reduction could be hypothesized. This would also result in lowering the immune reaction, which is one of the main causes of death, even allowing the combined use of other therapies profiting of the low infection level. The exact values of both the operation temperature and the exposition time should be determined through an appropriate set of tests.
Indeed, the heating approach might be obtained in different ways among which we point to the following configurations. In the first example, a linear array of microwave sources (at 2.15 GHz) is used to make a scan of the body of the patient. The power of the beam and the scan velocity determine the temperature increase inside the body.
Another configuration can be attained by using a square array of microwave sources which irradiate all the body. The power of the beam and the exposure time determine the temperature increase of the body. In both cases the cooling time after the irradiation is of the order of a few minutes. Of course, to determine the values of the involved parameters to be used an appropriate research strategy and accurate settings are required.
The process must be accompanied by a precise temperature control of the inner temperature of the body. This might be achieved by taking advantage on a simplified version of the so-called ‘Hospital in the Needle’. By combining nanophotonics, material science and optical fiber sensors (22-31), the Hospital in the Needle has been designed (27) in a configuration where a bunch of optical fibers can be integrated inside a needle. In the thinnest needle about ten optical fibers can be inserted, each of which is customized to perform a specific medical action. This is a strategy finalized to realize a single needle already shown to be able to perform in one shot all the following operations:
- Detection of cancer markers and miRNA
- High resolution localized ultrasound diagnostics integrated inside the needle
- Recognition of sick areas by linear and non-linear optical spectroscopy
- Ultrasound and laser surgery and ablation
- Localized optically controlled drug delivery
- System for automatic guidance of the needle
For the optical fibers that carry out laser surgery, it is possible to consider the products already available on the market. All the other sensorized optical fibers are instead innovative devices, essentially based on an emerging technology in the field of optical fiber sensors called 'Lab-on-Fiber'. This technology involves the integration of optical fibers with materials defined on a micro- and nano-metric scale, which transform the simple fiber into an effective device capable of performing the aforementioned functions. The optical fiber, thanks to its intrinsic properties (small dimensions, flexibility, low weight, biocompatibility, etc.), is well suited to be inserted inside needles and catheters for medical use. Optical fibers, in addition to ensuring the transmission of light signals, can be sensorized by integrating components and functional materials, typically around their tip. The choice of the type and size of the integrated component / material clearly depends on the physical / chemical parameter to be detected. The use of optical fibers for the development of medical probes is a common practice. However, all the devices proposed so far are designed to perform the single function. In other words, sensorized optic fibers are integrated on the single needle or catheter for the single function, thus limiting the flexibility of use. Moreover, the approaches proposed so far concerning hybrid systems, based on different technologies for the development of multi-function probes, have given rise to rather bulky devices, whose dimensions limit their use only in some particular contexts. Consequently, the miniaturized and minimally invasive devices are mono-functional, since the multifunctional ones are more invasive and not very flexible so that they can be used only in well-defined application contexts. So far this precision medicine strategy has been demonstrated suitable in the following cases: detection of thyroid cancer markers (25, 26), loco regional anesthesia (28, 29), optically driven drug delivery (ref), localized ultrasound diagnostics (30), optical activation of “optodrugs” and temperature control (22-24).
Accordingly, an optical fiber can be hosted inside a needle (a 26 gauge or even thinner needle is good enough) and it is possible to measure in this way the inner temperature of the body with an accuracy better than 0,1 °C. This can be easily made by inserting a temperature optical fiber sensor inside the needle. This solution allows to control the inner temperature of a body during the proposed treatment with a precision better than 0,1°C and with a very low invasiveness. In this way, a very thin needle (with a diameter smaller than one millimeter) can be used as a precise temperature sensor in order to keep under control the inner temperature of the body during the treatment thus avoiding any dangerous collateral effect.
More precisely the sensor is made by an optical fiber with its terminal part realized to be sensitive to the temperature. The termination of the fiber is provided by a temperature sensitive film or by a fiber bragg grating. Both the solutions have been showed suitable in a large variety of practical cases (REFS).
As a final remark, this approach might also be used for a fast, cheap and easy sterilization process. Nowadays sterilization involves either ultraviolet radiation or the use of a liquid disinfectants (e.g. Alcoholic solutions, quaternary ammonium derivatives). To sterilize a closed room, a simple nebulizer which injects in the room a mixture of simple water with sterilizing liquid might be proposed. Then, a small microwave source working at 2.15 Ghz (the frequency of microwave ovens) might be applied. A room with a surface of 30 m2 and a height of a 3 m has a volume of 90’ m3. In order to sterilize an environment like this about one liter of water would be needed. In SI units, cs = 1.005 + 1.82H where 1.005 kJ/kg °C is the heat capacity of dry air, 1.82 kJ/kg °C the heat capacity of water vapor, and H is the specific humidity in kg water vapor per kg dry air in the mixture To bring this water at a temperature of about 60 °C energy is needed. If the environment temperature is of about 20 °C an energy of about 40.000 cal equivalent to about 160.000 joules should be provided. If we assume a microwave source of about 500 watts (typical sources for a small microwave oven), we see that we need about 5 minutes to sterilize a room like this. The sterilization is safe because the microwave radiation is fully absorbed by the vapor and the operator is on the back of the source in a totally safe position.