Hui-jiuan Chen

Ultrasonic-aided fabrication of gold nanofluids

A novel ultrasonic-aided one-step method for the fabrication of gold nanofluids is proposed in this study. Both spherical- and plate-shaped gold nanoparticles (GNPs) in the size range of 10-300 nm are synthesized. Subsequent purification produces well-controlled nanofluids with known solid and liquid contents. The morphology and properties of the nanoparticle and nanofluids are characterized by transmission electron microscopy, scanning electron microscope, energy dispersive X-ray spectroscope, X-ray diffraction spectroscopy, and dynamic light scattering, as well as effective thermal conductivities. The ultrasonication technique is found to be a very powerful tool in engineering the size and shape of GNPs. Subsequent property measurement shows that both particle size and particle shape play significant roles in determining the effective thermal conductivity. A large increase in effective thermal conductivity can be achieved (approximately 65%) for gold nanofluids using plate-shaped particles under low particle concentrations (i.e.764 μM/L).

Radiofrequency heating of nanomaterials for cancer treatment: Progress, controversies, and future development

In recent years, the application of nanomaterials to biological and biomedicine areas has attracted intensive interest. One of the hot topics is the nanomaterial mediated radiofrequency (RF) hyperthermia or ablation, i.e., using RF fields/waves to heat tumor tissues treated with nanomaterials to destroy cancerous cells while minimizing the side-heating effect. However, there are currently many contradictive results reported concerning the heating effect of nanomaterials under a RF field. This paper provided a comprehensive review to nanomaterial mediated RF ablation from both experimental and theoretical aspects. Three heating mechanisms were discussed, i.e., laser heating, magnetic field heating, and electric field heating in RF spectrum, with the focus on the last one. The results showed that while diluted pure metallic nanoparticles could be heated significantly by a laser through the surface plasmon resonance, they cannot be easily heated by a RF electric field. Further studies are proposed focusing on nanoparticle structure and morphology, electromagnetic frequency and localized heating effect to pave the way for future development.

Conductivity and frequency dependent specific absorption rate

Recently, a number of contradicting results have been reported regarding the electromagnetic (EM) energy absorption by highly conductive materials in a liquid phase. The argument rises from the fact that higher conductive media absorb more electromagnetic energy; this however would be constrained by the localized field values that are dictated by the dielectric variations, which may reduce the absorption rate. Using salted water as an example, a systematic investigation of the mechanisms of EM absorption in the presence of highly conductive materials is conducted in this work. A theoretical model is developed, which is supported by both numerical and experimental studies. The influence of salt concentration, dielectric properties, boundary conditions, and EM frequency on the specific absorption rate (SAR) is carefully examined. The results show that the presence of salt in water modifies the dielectric properties significantly in the RF range, while the effect is less prominent in the microwave range. The...

Electromagnetic heating effect of aggregated gold nanoparticle colloids

Gold nanoparticles (GNPs) have been recently investigated intensively for potential hyperthermia treatment of malignant cancer cells in combination with radiofrequency (RF) electromagnetic (EM) fields/waves. However, many controversial results have been reported on whether GNPs can be heated by EM fields. It has been suggested that aggregated GNPs may be heated significantly by a RF field, which however has not been examined experimentally. This work proposes a novel electric treatment of mono-dispersed particles to create aggregated GNPs, and conducts an investigation of their bulk heating behavior under a 655 nm laser and a 13.56 MHz RF electric field. It is revealed that the heating rates of aggregated colloids are significantly higher than those of mono-dispersed GNPs for the 655 nm laser, whereas at 13.56 MHz, the heating effects are barely noticeable for both aggregated and mono-dispersed colloids. Various possible reasons are discussed and the negligible electric field enhancement is believed to be responsible at 13.56 MHz.

Laser heating of metallic nanoparticles for photothermal ablation applications

In order to search for a suitable frequency and material with higher photothermal efficacy for hyperthermia application in cancer treatment, a comparative study on laser heating of Au/Ag nanoparticles and Ag nanowires has been conducted. It is found that gold nanoparticles are more photothermal efficient in comparison with silver nanoparticles and silver nanowires at 450nm and 532 nm. Gold nanoparticles are more heated by 532 nm laser than 450 nm laser. In contrast, silver nanoparticles show slightly less temperature rise at 532 nm than 450 nm laser. For silver nanowires, no significant photothermal effect has been observed. Size-dependent effect study indicates that the absorption efficiency of single gold nanoparticles of larger diameter is higher than that of smaller diameter, in the diameter range of 0-50nm. A mathematical model for describing the heating profile in the heating sample has been built. The mathematical model can be utilized to predict the optimal treatment size of tumor.