We report on an investigation aimed to increase the efficiency of photodynamic therapy (PDT) through the influence of
localized surface plasmon resonances (LSPR's) in metal nanoparticles. PDT is based on photosensitizers that generate
singlet oxygen at the tumour site upon exposure to visible light. Although PDT is a well-established treatment for skin
cancer, a major drawback is the low quantum yield for singlet-oxygen production. This motivates the development of
novel methods that enhance singlet oxygen generation during treatment. In this context, we study the photodynamic
effect on cultured human skin cells in the presence or absence of gold nanoparticles with well established LSPR and
field-enhancement properties. The cultured skin cells were exposed to protoporphyrin IX and gold nanoparticles and
subsequently illuminated with red light. We investigated the differences in cell viability by tuning different parameters,
such as incubation time and light dose. In order to find optimal parameters for specific targeting of tumour cells, we
compared normal human epidermal keratinocytes with a human squamous skin cancer cell line. The study indicates
significantly enhanced cell death in the presence of nanoparticles and important differences in treatment efficiency
between normal and tumour cells. These results are thus promising and clearly motivate further development of
nanoparticle enhanced clinical PDT treatment.
We report experimental and theoretical results on the effect of electromagnetic coupling between metal particles in surface-enhanced Raman scattering (SERS). Model calculations of the near-field optical properties of Ag and Au nanoparticle-aggregates show that the electromagnetic surface-enhancement factor can reach 11 orders-of-magnitude in gaps between nearly touching particles. Single particles exhibit a much weaker enhancement, unless the particles contain extremely sharp surface protrusions. Data on spectral fluctuations in single-molecule SERS and measurements on the efficiency of nanofabricated SERS substrates give experimental support for the idea that an efficient interparticle coupling is a necessary requirement for an ultra-high surface-enhancement. We suggest a route for biorecognition induced coupling of metal particles for use in biosensing applications.