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 X 10(6) GM at 820 nm. Additionally, the HGNs have similar to 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.