Nonlinear Excitation of Tryptophan Emission Enhanced by Silver Nanoparticles
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We measured and analyzed the behavior of the fluorescence of tryptophan water solutions with and without silver nanoparticles, excited by one, two and three photon processes. Two different colloids with silver nanoparticles with distinct diameters (0.65 nm and 9 nm) were used in the experiments. Fluorescence quenching was observed with one and two photon excitation. However, upon three-photon excitation, significant fluorescence enhancement was observed in the colloid. In this case excitation of the amino acid is assisted by the nonlinear absorption of infrared light by the silver nanoparticles. In this paper we are proposing a new way to explore metallic nanoparticles to enhance autofluorescence of biomolecules.
KeywordsTryptophan Autofluorescence Metallic nanoparticles Nonlinear excitation
The authors would like to thank C. B. de Araujo for providing us with the NPs samples. Anderson S.L. Gomes and Diego Rativa wish to thank the Brazilian Agencies CNPq and CAPES for financial support of this work, which was also carried out under support of the Millennium Institute of Nonlinear Optics, Photonics and Biophotonics, as part of the MCT/CNPq Millennium Institute program and of the Nano Photonics Network. This work was also partially supported by the US Navy Bureau of Medicine and Surgery (D.L.F).
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