2011-Pos Board B741 Spectroscopic Properties of Intrinsic Proteins in Collagen Samples by using Gold-Nanoparticles and Two-Photon Excited Fluorescence Microscopy Manuela Gabriel 1 , Enrico Gratton 2 , Laura Cecilia Estrada 1,3 . Quantum Electronics Lab, Physics Department, University of Buenos Aires, Buenos Aires, Argentina, 2 Laboratory for Fluorescence Dynamics, Department of Biomedical Engineering, University of California, Irvine, CA, USA, 3 National Council of Scientific and Technical Research (CONICET), Buenos Aires, Argentina. Multiphoton microscopy provides optical sectioning for high-resolution imag- ing. In biological systems, most multiphoton microscopy studies have relied on two-photon excited fluorescence (TPEF) to produce images. In particular, TPEF from structural proteins has emerged as an invaluable tool for 3D imag- ing. However, depending on the fluorophores involved, the TPEF could be extremely weak, limiting TPEF use for thick-tissue applications. The physics and optical properties of noble-metal nanoparticles (NPs) is currently attracting much attention. The signal enhancement of molecules near a metal surface arises from the interaction with surface plasmon (SP) modes. These interactions also result in the shortening of the excited-state life- time improving the molecules’ photo-stability. The optical properties of the environment near a metallic NP are affected by the near-field electromag- netic-field. In the case of fluorescent molecules located at very short distances from a metallic surface, non-radiative energy transfer to SPs in the metal takes place; however, emission enhancement due to SP coupling still occurs at optimal distances from the NP. In this study, we use a broad range of excitation wavelengths (~800-900 nm) to demonstrate that absorption enhancement can also be achieved in unstained samples by using a combination of gold-NPs and a TPEF. The TPEF images of gold-NPs/collagen samples were used to determine the collagen absorption spectra and confirm enhancement factors >100, which provide promising new applications in fields such as tissue imaging, and fluorescence-engineering based on surface-enhancement effects. Our results suggest that even weakly intrinsic signals from structural proteins can be extremely-enhanced due to SPs coupling. The use of metallic NPs and TPEF in combination provides complementary in- formation that allows noninvasive, spatially localized, in-vivo characterization in unstained samples and tissues. Work supported by NIH grants P50GM076516 and P41GM103540, PICT0457- 2010 and UbaCyT20020100100719.