Nowadays, carbon nanotubes (CNTs) are considered as perspective nanoparticles for therapeutic application including selective photo-thermolysis of living cells, photo-acoustic, and thermo-acoustic imaging. Thermo-acoustic imaging refers to irradiating the sample with electromagnetic energy in the microwave and RF range and, in particular, provides deep tissue penetration and large sampling volumes.
The main aim of our investigations is to analyze the possibility of realizing high thermal contrast CNT-based agents for medical imaging technologies at RF frequencies. We present for the first time the calculations of electromagnetic absorption cross section of a finite length electrically small multi-wall carbon nanotube (MW CNT) and a single-wall carbon nanotubes (SW CNT) covered with thin lossy dielectric (molecular) coating at RF frequency. For MW CNT having lengths of several micrometers, we found that a strong screening of the inner shells by the outmost shells leads to a small absorption of electromagnetic energy by the inner shells. This can explain experimental results showing more effective absorption of SW CNTs’ suspension as compared with MW CNTs’ suspension of the same CNT mass fraction at RF frequency.
We developed a self-consistent electro-dynamical model for finite-length SW CNTs and MW CNTs covered with thin lossy dielectric coating. On the basis of this model we calculate the absorption cross-section of coated CNTs and analyze the influence of CNT length, coating complex permittivity and coating thickness on magnitude of absorption cross-section of coated CNTs. We found that due to the strong-near-field enhancement by finite-length CNT the energy dissipation in lossy dielectric coating can be enhanced more than 102 times. As a result, in particular, the absorption cross-section of coated metallic SW CNT of length 1 m can be 100 times larger than for an uncoated SW CNT. Thus, we can conclude that CNT coating can drastically change electromagnetic energy dissipation and should be taken into account at optimization of experimental scheme for thermo-acoustic imaging and for production of thermal cytotoxicity in malignant cells.