Professor Paul Chu Kim-ho

Breakthroughs in combating cancer and saving energy

By : Michael Gibb, Cathy Lau

At CityU, a team of multidisciplinary collaborative scientists has shared its recent contributions to this vital area of medical and materials science. Professor Paul Chu Kim-ho, Chair Professor in the Department of Physics and the Department of Materials Science and Engineering, and the team that he leads are developing breakthrough technologies for effective cancer treatment.

Trojan horse

The method is based on the study of photoluminescence and light scattering mechanisms, as well as the plasmonic properties of micro-nanostructures. Essentially this refers to the application of intense heat triggered by a photothermal process, i.e. electromagnetic radiation, to ablate cancer cells.

A schematic illustration of photothermal therapy shows macrophages loaded with Bi₂Se₃ nanosheets destroying cancer cells under near-infrared radiation.“Photothermal therapy is an emerging cancer treatment,” said Professor Chu. “It involves the targeted delivery of photothermal agents to tumours, and subsequent light irradiation to produce a high local temperature that can destroy tumour cells.”

The key innovation developed by Professor Chu and his team is the discovery of two effective types of carriers of photothermal agents: Bi₂Se₃- laden-macrophages and Nile blue dye with black phosphorus.

(a) Infrared thermal images of the mice
(b) Curves of tumour temperature versus time
(c) Tumour growth curves of different groups of mice Macrophage is a kind of good-guy white cell that tackles errant material in the body that has the potential to cause harm, while Nile blue dye is a well-known agent that can differentiate between, say, fatty acids and lipids by staining with colour.

The agents are delivered rather like the huge wooden horse that transported armed Greeks into the unsuspecting city of Troy: into the body where they can bomb potential cellular threats.

“When the ‘bombs’ interact with near-infrared light, the temperature rapidly increases, killing the tumours,” said Professor Chu.

Minimising cancer recurrence

Photothermal therapy was a highly promising means of tackling cancer, Professor Chu added, for three main reasons: it was minimally invasive, fast-acting, and easily combined with other therapeutic approaches. In addition, it appears to help to abate recurrence. This is highly significant since once a course of cancer treatment has been completed, doctors have to watch out that malignant cells don’t reappear at a later stage.

But in vitro trials run by Professor Chu and his team suggest that the possibility of the cancerous cells returning could be minimised using this technology.

“In trials, the tumours in mice were completely destroyed and removed, and there was no recurrence until the end of the experiment,” explained Professor Chu.

Controlling heat transmission

The photoluminescence, light scattering mechanisms and the plasmonic properties of micro-nanostructure techniques used to take on cancer have potential in different fields, too. One significant application is in thermochromic smart coating.

The VO₂ / TiN coating blocking infrared (IR) light shows strong illumination at 28^oC but is IR transparent under weak irradiation conditions or at a low temperature of 20^oC.Thermochromic refers to an acute sensitivity to temperature, i.e. change of colours when heat is applied or reduced. One of the best examples from daily life that most of us are familiar with is when the light on an electric kettle changes to red to indicate that the water has boiled.

So smart coating works basically as a transparent blind to control heat transmission and minimise the need for air conditioning or heating.

“What we have done at CityU is to combine the properties of TiN [titanium nitride] nanoparticles and VO₂ [vanadium dioxide]. TiN nanoparticles absorb light quickly and increase the local temperature, while VO₂ changes its phases depending on different temperatures in order to block heat or allow heat to pass through,” Professor Chu said.

The smart coating blocks heat under strong illumination at 28ºC, but are heat transparent in weak irradiation conditions or at a temperature of 20ºC or lower.

Possible applications are coating windows in buildings or vehicles with the combined TiN nanoparticles and VO₂ properties as a means to save energy, which is of course a crucial matter in this era of sustainability and conservation.

Working in partnership

The collaborative aspect of these areas of research conducted by Professor Chu and his team into photoluminescence, light scattering mechanisms and plasmonic properties of micro-nanostructures is hugely rewarding, he said. The composition of his team highlights the highly collaborative aspects of research at CityU and the rich fruit from partnerships with scientists in mainland China and Germany.