▲ Prof. Young Keun Kim’s research team (from left, Prof. Young Keun Kim, Yu Jin Kim, and Bum Chul Park)

A research team led by Prof. Young Keun Kim from Korea University developed new technology using fluorescence detected in the cellular system and the photothermal effects of Fe3O4 nanoparticles (NPs).

* Photothermal therapy: A therapy that embeds nanoparticles into tumors and uses heat generated by near infrared (NIR) laser irradiation to kill cancer cells. The therapy has drawn attention as an alternative cancer treatment with lower adverse effects, such as hair loss or vomiting, than surgical operation or other existing therapies. 
* Photothermal agent: An agent to generate heat by the application of external photonic stimuli.

Au NPs have mainly been focused on for photothermal therapy, for they can easily generate heat by absorbing visible and NIR light. However, exposure to low doses of irradiation lessens the effects of Au NPs, and a low-temperature phase transformation weakens their structural stability. As a result, Fe3O4 NPs have recently attracted attention as a photothermal agent that could replace Au.

The research team induced the photothermal effect of Fe3O4 NPs by irradiating an NIR laser. The heat generated during the process formed π-conjugated chains, inducing fluorescence through a series of main and side-chain cleavage reactions of polymers with the aliphatic chain.

▲ The photonic reactions of Fe3O4 NPs and polymer composites leading to π-conjugated chains and fluorescence

* π-conjugated system: An electron structure with alternating π-bonds of molecular orbits when two atoms or more form an electron pair and form a molecule by sharing electrons (sharing bonds).
* Conjugated polymer system: A polymer with alternating single and double bonds that form π-conjugated chains. Low band gap conjugated polymers have the properties of semiconductors, emitting light in the visible range.

Fluorescence also occurred when NPs were introduced into the cellular system because organic materials worked as polymers and changed the cells into π-conjugated chains. In addition, fluorescence emission changed in tandem with the intensity of the laser and size of Fe3O4 NPs with a stronger intensity observed in large-sized NPs.

▲ Fluorescence emission from the cells by the photonic reaction of Fe3O4 NPs by size

“Our findings imply that when Fe3O4 NPs are applied to photothermal therapy, we can monitor whether the therapy is properly performed. The technology promises a new possibility for photothermal therapy,” said Prof. Young Keun Kim.

This research received financial support from the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education. Their findings were published in the international journal Small on July 27 (corresponding authors: Kim Yeong Geun & Yu Jin Kim; First author: Bum Chul Park).