In their review Silvio Dutz and Rudolf Hergt, from Technische Universität and the Photonic Institute in Germany, describe how thermal treatment was first identified as a medical tool 150 years ago when Busch observed the damage heat causes to tumour cells while healthy cells are unharmed. When nanoparticles are used to deploy this heat, as opposed to a water bath, microwave irradiation or other external devices, they offer the advantage of being able to navigate the intricacies of the body to the tumour site non-invasively for targeted localized thermal treatment.

How local is nanoscale energy dissipation?

So "How localized are energy dissipation processes in nanoscale interactions?" asked Sergio Santos at the Laboratory for Energy and Nanosciences, UAE, and colleagues at Universitat Politècnica de Catalunya Avenida Bases and Centre d’ Investigacío en Nanociència i Nanotecnologia in Spain, Leeds University in the UK and MIT in the US. They define a figure of merit to quantify how localised nanoscale thermal heat dissipation processes, are defined by the ratio of the area of the interaction and the density of energy dissipated.

"We have shown that neither the amount of energy dissipated in the interaction nor the phase contrast are sufficient criteria to establish whether the interaction is highly localized," they conclude. The nanoscale interactions they considered were those in an atomic force microscope system but their conclusions suggest that their results should provide an insight into energy dissipation processes in nanoscale dynamics more generally as well.

In photothermal treatments heating is achieved on account of the absorptive qualities of the nanoparticles that give rise to heat when irradiated or illuminated. Pustovalov from the Belarusian National Technical University, Astafyeva from the National Academy of Sciences of Belarus and Jean from Tübingen University in Germany modelled the optical properties and heating of gold nanoparticles and gold-silica core-shell nanoparticles in the context of photothermal medical treatments using Mie theory. The calculations supported the potential for therapeutic use of the nanoparticles and identified parameters for implementing photothermal treatment most effectively.

Finding new magnetic nanoparticle materials

Over recent years magnetic nanoparticle hyperthermia has attracted increasing interest as a tumour treatment. Here heating is deployed by the dissipation of heat through hysteresis and relaxation losses in a magnetic nanoparticle when a magnetic field is applied. The most commonly used materials are iron oxide, in particular magnetite nanoparticles, which are prepared by chemical routes. But as P&eecute;rigo and colleagues in Brazil point out in a recent paper "the possibility of obtaining nanoparticles by physical methods, even by recycling magnetic compounds, should also be considered."

They suggest that research into the viability of physical approaches would open new possibilities to obtain new materials with suitable magnetic properties compared with those currently available; and give a beneficial impact in reducing the consumption of new raw material. They demonstrate that NdFeB-based nanoparticles sintered from bulk alloy also exhibit suitable properties for magnetic nanoparticle hyperthermia.

Magnetism advances in medicine

In addition magnetic nanoparticles can be used for magnetic resonance imaging and targeting by magnetically tagging tumour cells and this has attracted a great deal of study into the development of multifunctional nanoparticles, where the magnetic characteristics are exploited for imaging and diagnostics, and targeted hyperthermal treatment. Shanta Singh and colleagues at the Indian Institute of Technology Bombay in India went a step further and successfully used the heating effect from the hyperthermia for drug release as well.

"Loss is nothing else but change, and change is Nature's delight" Marcus Aurelius, "Meditations".

In their review Dutz and Hergt provide a thorough overview of research into the mechanisms governing magnetic nanoparticle hyperthermia, preparation of the nanoparticles and their biocompatibility, administration, targeting and clinical applications. In posing the question "Is nanoparticle hyperthermia a promising tumour therapy?" Dutz and Hergt respond "Not yet!" and conclude that the main challenges now lie with biological and medical research for ensuring safe targeted administration of the nanoparticles.

But the prospects in the field look good, suggesting a life-saving application that exploits heat losses in nanomagnetic systems is not impossible. As Marcus Aurelius famously said in his Meditations, "Loss is nothing else but change, and change is Nature's delight."