Plasmon Resonant Two-Photon Luminescence Inducing Photosensitization and Nonlinear Optical Microscopy In Vivo by Near-Infrared Excitation of Au Nanopeanuts

Photodynamic therapy (PDT) provides a potential therapeutic approach for killing malignant cell/solid tumors, but currently approved photosensitizers (PSs) are generally excited by visible light, limiting the penetration depth in tissues. It is necessary to develop a near-infrared (NIR) responsive photodynamic platform, providing maximum tissue penetration. Here, we present a gold nanopeanut platform exhibiting dual functions of NIR PDT and two-photon luminescence imaging. The nanopeanut with a size less than 100 nm exhibits two distinct NIR surface plasmon absorption bands at approximately 1110 and 1300 nm. To perform PDT, we conjugated commercial toluidine blue O (TBO) PS on the surface of the nanopeanuts. With spectral overlap, the 1230-nm femtosecond Cr: forsterite laser can excite the surface plasmons of nanopeanuts, transfer energy to TBO, and generate singlet oxygen to kill cells. Moreover, the plasmon resonance-enhanced two-photon luminescence of nanopeanuts can be used to map their delivery in vivo. These results demonstrate that the PS-conjugated gold nanopeanut is an effective theranostic system for NIR PDT.

Nonlinear imaging of whispering gallery modes in GaN microwires

In this work non-scanning far-field nonlinear optical microscopy is employed to study the whispering gallery modes in tapered GaN microwire resonators. We demonstrate the confinement of whispering gallery modes under near-infrared excitation with the photon energy close to half of GaN bandgap. Our results indicate the enhancement of yellow-green luminescence by whispering gallery modes in GaN microwires.

Characterization of medieval-like glass alteration layers by laser spectroscopy and nonlinear optical microscopy

Historical glass-based objects undergo, since the time of their manufacture, different degradation phenomena that are related to their composition and to the environment to which they were exposed. Three-dimensional (3D) structural and chemical characterization of the degradation layers is important to select the most adequate conservation strategies for glass objects. Optical microscopy (OM) is the most frequently used non-destructive method to examine the surface of historical glasses; however, the 3D structural assessment of alteration layers requires applying the destructive modality of this technique to conduct a cross-sectional study. In this work, a different approach for structural and compositional characterization of alteration layers on model medieval-like glasses is presented, based on the combination of the laser spectroscopies of laser-induced breakdown spectroscopy (LIBS), laser-induced fluorescence (LIF) and FT-Raman, and the emerging, cutting edge technique of nonlinear optical microscopy (NLOM) in the modality of multiphoton excitation fluorescence (MPEF). The results obtained through this multi-analytical photonic approach were compared with those retrieved by examination of the surface and cross sections of the samples by OM and scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM–EDS). While the combination of LIBS, LIF and FT-Raman served to assess the composition of the various alteration layers, the use of MPEF microscopy allowed the non-destructive determination of the thicknesses of these layers, showing for both thickness and composition a good agreement with the OM and SEM–EDS results. Thus, the proposed approach, which avoids sample preparation, illustrates the capability of non-destructive, or micro-destructive in the case of LIBS, laser spectroscopies and microscopies for the in situ study of glass objects of historic or/and artistic value. Graphic Abstract