06 May Temperature Sensing in liquid samples
As it is well known, magnetic hyperthermia is based on magnetic material heating by the application of an alternating magnetic field (AMF) due to the energy absorption which is transformed into heat. Then, the heat induces an increment in the sample’s temperature which has to be recorded to determine the specific power absorption (SPA), also known as Specific Absorption Rate (SAR).
The temperature sensing system is not a trivial issue working in the presence of an AMF for magnetic hyperthermia applications. Sensors as lab thermometers or thermopars cannot be used since they will be heated when the AMF is activated. However, optical temperature sensors are designed to be able to work in a radio frequency (RF) environment without interference in their measurements.
Our device uses Neoptix T1 optical temperature probes with a small optical fiber diameter allowing their use in small volumes. This probe has a response time of less than 500 milliseconds, and it has an outer protective jacket made of PTFE Teflon™ with a diameter of 1.15 mm. This sensor operates in a temperature range from -270 to 250 ºC and its uncalibrated accuracy is ±1 ºC.
This probe is commonly used with the Calorimetry CoilSet which is prepared to place inside 1.5 mL vials as can be observed in Image 1. The sample holder column with fiber optic probe provides 5% homogeneity across the sample and thermal insulation. The holder is prepared to analyze different volumes of fluid; mean field distribution across the sample can differ, given that while field distribution regarding the sample holder is steady, sample distribution across the sample holder is not. It is really important to place the sample in the homogeneous field area to avoid this source of measurement errors. For this purpose, an accessory is available to center the sample respect to the field distribution. This accessory contains a set of rings of different heights to adjust the sample position for a specific volume of sample.
The optical temperature probe is connected with MaNIaC, the software which allows the execution of experiments and the measurement of temperature, as shown in Image 2.