The role of hot electrons in photothermal therapy


Photothermal therapy (PTT) is a treatment modality for cancer which is currently in clinical trials. In PTT, gold-based nanoparticles convert near-infrared light into heat due to the energy release of “hot” electrons upon irradiation. Excessive heat causes cell-death. However, recent work from photovoltaic research demonstrates that hot electrons can instead be extracted and used to drive redox chemistry. It is highly plausible that these hot electrons also play a significant role in PTT, through damaging redox reactions with various biomolecules and production of reactive oxygen species (ROS). However, the possibility for hot-electrons contributing to cell-death has thus far been ignored. It is therefore important to re-evaluate our understanding of the underlying mechanisms of PTT in the process of developing next-generation phototherapies.
In order to fill this knowledge gap, this proposal focusses on preparing water-soluble nanoparticles based on zirconium nitride (ZrN) and hafnium nitride (HfN). These materials are optically similar to gold, but the hot electrons live for up to 1000× longer. These extended lifetimes significantly enhance the rate of hot-electrons reactions at the expense of heat generation, thereby shifting the balance towards redox-based cell death. Water-soluble and biocompatible ZrN/HfN nanoparticles will be synthesized and their interaction with biology will be studied. Through a combination of systematic photophysical and photobiological studies, the electron transfer reaction and the individual contributions of heat and redox chemistry will be examined in order to get insight into the biological relevance of the hot electron. The research will contribute valuable knowledge to the research fields of photopharmacology and nanomedicine. From an application viewpoint, a combination of heat and redox chemistry in ZrN and HfN nanoparticles is expected to synergistically enhance the therapeutic efficacy, and lead to a next-generation phototherapeutic nanodevice.


Project number


Main applicant

Dr. S.H.C. Askes

Affiliated with

NWO-institutenorganisatie, AMOLF, Nanoscale Solar Cells

Team members

Dr. S.H.C. Askes


01/09/2019 to 31/07/2022