Young scientists offer nanosized optical sensors for temperature measurements
A new paper by the Laboratory of Hybrid Optical Sensors saw light in Materials in December 2022.
This lab is one of the six new entities opened at KFU in 2022 as part of the federal Development of Human Capital Program (New Medicine topic).
Laboratory head Maksim Pudovkin explains, "One of the topical tasks of medicine is accurate temperature control in a local area of the body with characteristic linear dimensions of several micrometers, for example, in a cell. This is necessary, in particular, for hyperthermia of cancerous tumors. During this procedure, the tumor is heated by laser radiation. At the same time, the temperature inside the tumor should not exceed 40-42 degrees, since overheating can have a strong inhibitory effect on healthy tissues. At the same time, inefficient heating will not produce the proper therapeutic effect. Thus, it is necessary to strictly control the temperature inside the heated object. It's quite difficult. And since this must be done contactlessly, traditional methods of measuring temperature in this situation are ineffective."
One such solution is the use of nanosized luminophores which luminesce differently depending on temperature.
"If these sensors are introduced into the area under study, then, by analyzing the luminescence signal, information about the temperature can be obtained. For such applications, especially for hyperthermia, it is very important that optical detection be carried out in the so-called transparency window of biological tissues. It is also important to increase the temperature sensitivity of the phosphor luminescence parameters for more accurate temperature detection," says Pudovkin.
What is a 'biological window'? The scientist informs, "Biological tissues of living beings almost do not transmit ultraviolet and visible light (the penetration depth is not more than 2 millimeters), however, red and infrared radiation can penetrate the skin to a depth of 1 to 5 centimeters. These types of radiations lie in the range of 700-1,300 nanometers. This range is called the biological window. A number of optical, therapeutic and diagnostic systems operate in this window."
To increase the efficiency of sensors, a deeper understanding of physical fundamentals should be achieved, opines the team leader, "According to our previous studies, sensors based on Nd3+/Yb3+:YF3 nanoparticles have shown high performance, but the mechanism of temperature sensitivity remains unclear. The YF3 compound here is an optically inert matrix in which Nd3+ and Yb3+ activator ions are placed. The Nd3+ neodymium ion is able to absorb laser radiation at a wavelength of 790 nanometers and re-emit it as a luminescence signal, as well as transfer the energy received from laser radiation to the Yb3+ (ytterbium) ion, which, in turn, emits its own luminescence signal. The efficiency of energy exchange between activating ions depends on temperature. Thus, the luminescence parameters of sensors also depend on temperature. This phenomenon usually explains the temperature sensitivity of a number of existing sensors based on the Nd3+/Yb3+ ion pair and other matrices."
During experiments, the scholarly collective has found a number of unusual phenomena not fully explained by the abovementioned dependencies—that is, the reason may be in thermal expansion.
"When Nd3+/Yb3+:YF3 is cooled, the nanocrystals shrink and the distances between the activator ions decrease, which leads to an increase in the efficiency of their interaction. This is evidenced by a number of our experiments. At the same time, for other fluoride matrices, apparently, this effect, if present, is not very significant compared to YF3. The sensors are Nd3+, Yb3+:YF3 nanoparticles approximately 200 nm in size. For their practical application, it is necessary to develop an appropriate stationary experimental setup, which in the general case includes: a laser, detectors and a computer, and we will work on it in 2023 and 2024 in our lab," concludes Pudovkin.
Based on the obtained data, the optimal concentrations of activator ions were determined and sensors were created that have the following competitive advantages: relatively high absolute temperature sensitivity in the physiological temperature range (maximum value 0.5 percent/K); high stability (during 12 cycles of cooling to -196 degrees / heating—up to 45 degrees there is no degradation of the spectral and kinetic characteristics of Nd3+, Yb3+:YF3 nanoparticles); multifunctionality (sensors show high sensitivity values in a wide temperature range from 196 to 45 degrees, which makes them a promising material for sensors in other areas, including the space industry); the sensors function in the 'biological window'.
More information:
Nd3+, Yb3+:YF3 Optical Temperature Nanosensors Operating in the Biological Windows, www.mdpi.com/1996-1944/16/1/39#
Provided by Kazan Federal University