1 research outputs found
Nonlinear Optical Properties of Thiolate-Protected Gold Clusters
Thiolate-protected gold clusters
are promising candidates for imaging
applications due to their interesting, size-dependent properties.
Their high stability and the ability to functionalize the clusters
with biocompatible ligands render the clusters interesting for various
imaging techniques such as fluorescence microscopy or second-harmonic
generation microscopy. The latter nonlinear optical effect has not
yet been observed on this type of ultrasmall nanoparticle. We hereby
present second- and third-harmonic generation and multiphoton fluorescence
of two thiolate-protected gold clusters: Au<sub>25</sub>(SCH<sub>2</sub>CH<sub>2</sub>Ph)<sub>18</sub> and Au<sub>38</sub>(SCH<sub>2</sub>CH<sub>2</sub>Ph)<sub>24</sub>. At a fundamental wavelength of 800
nm, the Au<sub>38</sub>(SCH<sub>2</sub>CH<sub>2</sub>Ph)<sub>24</sub> cluster is active. In contrast, Au<sub>25</sub>(SCH<sub>2</sub>CH<sub>2</sub>Ph)<sub>18</sub> does not yield significant SHG signal. We
ascribe this to the center of inversion in the Au<sub>25</sub> cluster.
Measurements on chiral Au<sub>25</sub>(capt)<sub>18</sub> (capt: captopril)
gave an SHG response, supporting this interpretation. We also observed
third-harmonic generation at a fundamental wavelength of 1200 nm.
At 800 and 1100 nm, the clusters decompose after short illumination
time but are stable at illumination at 1200 nm. This may be exploited
in combined deep tissue imaging and photothermal heating for theranostics
applications