RADIO-FREQUENCY ELECTROMAGNETIC CHARACTERIZATION OF BIOMATTER AND NANOPARTICLES FOR BIOMEDICAL APPLICATIONS

The influence of radio-frequency (rf) electromagnetic fields on biological tissues plays a critical role in their diagnostic and therapeutic applications. These include hyperthermia and rf ablation modalities for cancer, in which cell temperatures are increased to 41-46ºC and above 56ºC respectively. However, optimizing tumor’s obliteration efficiency and selectivity is a challenge and is accomplished by functionalized magnetic/nonmagnetic nanoparticles as rf absorption enhancers. Since there is no explicit elucidation of the nanoparticles’ heating mechanism, this dissertation focuses on the characterization of their heating efficiency. Rf losses due to the interaction of nanoparticles in aqueous media with both electric (Erf) and magnetic (Hrf) fields were investigated using a low input power hyperthermia-setup designed with a high quality factor LCR resonator to generate Erf and Hrf fields up to 100 kV/m and 50 kA/m, in 12-50 MHz frequency range. To find the specific absorption rates (SAR), measurements of temperature change versus time were done on the metallic, dielectric and superparamagnetic nanoparticles, as they constitute the multifunctional nanoconstructs. Magnetic SAR for SPIO was calculated as 4 kW/kg and electric SARs for gold, silica and SPIO were calculated as ~103, 2 and 27 kW/kg respectively. This demonstrates that at MHz frequencies SARs for nanoparticles were overestimated by previous studies, which ignored ohmic heating of the conductive dispersion medium. From the analysis of non-magnetic nanoparticles, the enhanced dipole fields on gold were found three times higher than silica. The rf loss was strongly ascribed to the interaction of dipole fields with the electrical double layer (EDL) at the particle-electrolyte interface, which was confirmed by synergistic heat enhancement through EDL modification using physiologically relevant proteins. In order to understand the nature of EDL at a charged surface, investigations of nonlinear rf responses of bio-electrolytes placed within gold electrodes of a capacitor as a part of frequency-adjustable LCR parallel-resonant circuit were reported. Measurements were done using the intermodulation distortion technique. It was confirmed that the measured intrinsic nonlinear effect originates from the electrode-electrolyte interface and is ion-concentration dependent. The third-order coefficient of the power series of the nonlinear transfer-function was related to capacitive and conductive components of the EDL’s impedance.