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When gold is shining even brighter

Gold nanoparticles have attracted much attention in ex vivo and in vivo biological imaging due to surface-enhanced Raman scattering of attached molecules and the superior properties of gold for bio-labelling. However, gold has been treated as non-luminescent for a long time, thus inhibiting it’s use as a luminescence marker like fluorescent semiconductor nanoparticles. But this restriction could be no longer valid. Chemists and physicists at Humboldt University and Free University of Berlin could show that gold nanoparticles exhibit a bright luminescence with multiphoton near-infrared excitation.|1S&L~w
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Maik Eichelbaum et al. report in Nanotechnology that monodispersed gold nanoparticles can be embedded and stabilized in 350 nm thin silicate-titanate films prepared by a sol-gel spin-coating technique and subsequent annealing at 300 °C or, alternatively, near-infrared (NIR) femtosecond laser irradiation. The particle size ranges between 5 and 100 nm and can be tuned by changing the gold concentration. Excitation of films with the 795 nm fundamental of a Ti:sapphire femtosecond laser produces a strong white luminescence. The analysis of the laser power dependence indicates that the gold nanoparticle emission is induced by the absorption of three NIR laser photons. Electron microscopy investigations further show that the nanoparticles are not only embedded within the glassy nanolayer but are also located on the film surface. Hence, the particles are accessible to analyte molecules. $c5h@t)lk2Mk5a
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TEM imageBecause of the transparency and reduced cell damage to human and animal tissues in the NIR spectral range, the multiphoton-induced photoluminescence of gold nanoparticles could become a powerful alternative to organic and semiconducting fluorophores in biological imaging. Furthermore, the writing of gold nanoparticles containing structures in thin films by NIR laser irradiation and the readout of the luminescence could become very promising for optical memory applications.

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