Two-Photon Photoluminescence and Photothermal Properties of Hollow Gold Nanospheres for Efficient Theranostic Applications

The ability to successfully pinpoint and subsequently destroy cancer cells using biologically inert material and noninvasive methods is ideal for low-risk procedures. One way to accomplish this is using plasmonic gold nanoparticles, which have two-photon photoluminescence (2PPL) and photothermal properties that can be triggered by deep-tissue-penetrable near-infrared (NIR) light (650–950 nm). Herein, the first 2PPL of hollow gold nanospheres (HGNs) is reported using multiphoton luminescence microscopy. The two-photon action cross-section of the HGNs, using gold nanorods (GNRs) as a reference, is 1.02 × 10⁶ GM at 820 nm. Additionally, the HGNs have ∼0.75 times the 2PPL quantum yield of GNRs. The larger two-photon action cross-section and lower quantum yield correspond to a higher efficiency for heat generation desired for photothermal conversion applications. To this end, the 2PPL and photothermal properties of HGNs can be applied toward simultaneous cancer cell imaging and photothermal therapy (PTT). HGNs bioconjugated with folic acid–PEG–thiol (HGN-FA) selectively bind to the overexpressed folate receptor of cervical cancer HeLa cells and the 2PPL from HGN-FA captures high-resolution cancer cell images. Subsequent power increase and laser scanning dwell time result in highly efficient photothermal destruction of cancer cells. Using femtosecond laser pulses, microseconds of laser exposure generate well-localized superheating of HGNs, yielding subcellular thermal damage and cell death

Improved Stability of Organometal Halide Perovskite Films and Solar Cells toward Humidity via Surface Passivation with Oleic Acid

Organometal halide (OMH) perovskites are highly promising for photovoltaic (PV) and other applications. However, their instability toward environmental factors such as humidity presents a major challenge in their potential commercial use. In this study, we developed a method to modify the surface of CH₃NH₃PbI₃ perovskite films by spin coating oleic acid (OA) to create a water resistant layer that results in enhanced stability and PV performance. The OA-surface passivated perovskites were studied using FT-IR spectroscopy, UV–vis absorption spectroscopy, and X-ray diffraction (XRD). The samples were aged in dark humid air at ∼76% relative humidity (RH) for 4 weeks. The surface passivated films showed minimal signs of decomposition, and the PV devices showed better performance than the unpassivated devices. A possible explanation is the carboxyl group (−COO^–) of OA binds to surface Pb²⁺ and/or CH₃NH₃⁺ to both passivate these surface defect sites, resulting in the formation of a thin layer of OA with their hydrophobic tail away from the perovskite film surface that effectively prevents water molecules from reaching the perovskite