## Materials and Methods  
### Experimental Setup  
The radiofrequency ablation setup consisting of an RF (radiofrequency) generator, Micron Optics, 16-element array FBG optical fiber, and commercially purchased porcine liver is schematically depicted in Figure 1 with the photographic view of the experimental setup in Figure 2. The customized hybrid radiofrequency ablation (RFA)/Microwaveablation (MWA) generator for research purposes (LEANFA S.r.L, Ruvo di Puglia, Italy, Hybrid RFA/MWA module) coupled with the RF or MW applicator depending on the application was used as a thermal ablation source. This study employed the RF module with a radiofrequency applicator ending with the conical in shape and 0.5 cm in length with an active electrode (AE) at the tip. The dimensions of the applicator are 0.3 cm in diameter and 16 cm in length. The passive electrode (PE) is a metallic plate positioned underneath the tissue. The porcine liver used for ablation purposes was commercially purchased from the butchery shop and utilized according to the European protocol of \"Three Rs\" [10]. The phantom was adjusted to room temperature at 22-25 \({}^{\circ}\)C for several hours before use to obtain the conditions close to the body temperature. The initial temperature was measured employing the contact thermocouple IKA ETS-D5. The porcine liver was exposed to the radiofrequency ablation (RFTA) using an applicator connected to an RF generator with the operating frequency of 450 kHz and at the power of 50 W maintained in the same conditions for all sets of trials. The RF generator was maintained at a'safe mode on' state that allowed to automatically terminate the power while reaching the set tissue impedance of 800 \(\Omega\) controlled by the impedance meter, included within the RF applicator. Figure 1: Schematic representation of the radiofrequency ablation setup of the porcine liver using a 16-element array fiber Bragg grating (FBG) temperature sensing system. The setup consisted of: (1) an RFA generator; (2) Micron Optics; (3) computer; (4) porcine liver; (5) 16-element FBG array. Figure 2: The photographic view of the experimental setup of the radiofrequency ablation mediated with iron oxide nanoparticles. The 16-element array FBG is placed in x-direction on the surface of the porcine liver phantom. The numberings of the equipment, porcine liver and optical fiber are located and marked as in Figure 1.  
The 20 nm iron oxide nanoparticles at different concentrations were introduced ex vivo on the tissue surface. Thermal ablation experimental trials were repeated at 10 replicates for each set of concentrations starting from 1 mg/mL to 10 mg/mL for both agarose and chitosan solvents. Two types of solvents, such as 0.2% agarose solvent and 0.5 wt. % chitosan solvent, were exploited to derive experimentally the best performing solvent and investigate the heating mechanism. The stock solvents for each concentration were prepared and finally, 100 \(\upmu\)L of the nanoparticle solvents were injected on the porcine liver surface using a syringe. The experiments lasted for 120 s for all trials. The temperature sensing system consists of 16-element array FBGs attached alongside with applicator and its tip in close proximity in x-direction as shown in Figure 2 to observe the temperature change. The whole distance between the first and the last FBGs was 7.61 cm, which can be considered as the sensing area of the experiment. The measuring fiber was analyzed using an optical sensing interrogator (si255, Micron Optics) at the continuous measurement conditions (1 kHz speed). The interrogator was set to monitor 16 peaks on the measured spectrum, using fast-tracking polynomial fitting over a spectral threshold [20]. The time step between each measurement was equal to 1 millisecond. After converting the spectral shifts of each peak to thermal data, it was possible to reconstruct the temperatures of the FBGs along the length of the fiber during the heating procedure.