Comparison of complex permittivities of isotonic colloids containing single‐wall carbon nanotubes of varying chirality

Abstract

The application of bio-compatible, conductive nanoparticles in combination with radiofrequency (RF) irradiation to raise tissue temperatures between 40 and 60 °C for hyperthermia and ablation spurred interest in the complex permittivities of isotonic nanoparticle-based colloids. Nanoparticles with large aspect ratios and high permittivities increase the bulk permittivity of the colloid and RF losses at the macroscopic scale. The complex permittivities of isotonic colloids with and without single-wall carbon nanotubes (SWCNTs) containing either metallic, semiconducting, or mixed chiralities were measured from 20 MHz to 1 GHz at room temperature. The colloids were made with one of three different isotonic solvents: phosphate buffered saline (PBS), and Dulbecco's modified eagle medium (DMEM) with and without 0.5% weight/volume bovine serum albumin to simulate cytosol and blood, respectively. The concentration of elemental carbon from the SWCNTs in the colloids ranged from 16 to 17 mM. The permittivities were corrected for electrode polarization effects by fitting the data to the Cole-Cole relaxation model with a constant phase angle element. The presence of SWCNTs increased both the real and imaginary components of the permittivities of the colloids. For all three solvents, the direct current (DC) components of the real and imaginary permittivities were greatest for the colloids containing the mixed chirality SWCNTs, followed by the colloids with semiconducting SWCNTs, and then metallic SWCNTs.

Observation of the microwave near-field enhancement effect in suspensions comprising single-walled carbon nanotubes

“…As shown in figure 2(a), the effective permittivity of the m-CNT suspension satisfies (6) for infinitely conductive nanoparticles. In figure 2(b), the value Im[ε ef f ] for the s-CNT based suspension decreases as frequency grows, in accordance with (17). The strong difference between the EM response of m-and s-CNTs is caused by the different mechanisms of EM interaction: s-CNTs are slightly polarized and strongly absorb energy by itself, while m-CNTs are strongly polarized and induce a strong near-field that results in absorption enhancement in the surrounding host medium [2].…”

“…We have neglected the real part of the permittivity Re[ε s ] in (17) as it is much less than both Re[ε h ] and Im[ε s ], and practically does not contribute to the suspension permittivity (see figure 2(b) below).…”

“…Since its theoretical prediction, the near-field enhancement effect has been observed in the infrared range (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30) via absorption enhancement of biomolecules absorbed on single-walled carbon nanotubes [6]. The aim of the present work is to specify conditions for the near-field enhancement effect in the microwave range.…”

“…Currently there are several obstacles which prevent the wide application of microwave spectroscopy to the study of CNTs: (i) only small CNT densities (< 1 mg/ml) can be achieved in well-dispersed suspensions [14] resulting in small differences between the electromagnetic response of liquid media with and without CNTs [15,16,17,18,19,20]; (ii) dispersion of CNTs in the solvent is accompanied by CNT length reduction [21]; and (iii) at present there is a lack of understanding and difficulties in the interpretation of the data from microwave measurements.…”

Technical Note: T1 and T2 and complex permittivities of mineral oil, silicone oil, and glycerol at 0.35, 1.5, and 3 T

“…Temperature corrections in the complex permittivity measurements are required since there were small variations in temperature between the samples. We estimate the temperature corrections would be <2% for all samples . We expect the measured permittivities should be within 6% of the actual value based on the probe accuracy and measurement repeatability.…”