Enhanced Plasmonic Resonance Energy Transfer in Mesoporous Silica-Encased Gold Nanorod for Two-Photon-Activated Photodynamic Therapy

Abstract

The unique optical properties of gold nanorods (GNRs) have recently drawn considerable interest from those working in in vivo biomolecular sensing and bioimaging. Especially appealing in these applications is the plasmon-enhanced photoluminescence of GNRs induced by two-photon excitation at infrared wavelengths, owing to the significant penetration depth of infrared light in tissue. Unfortunately, many studies have also shown that often the intensity of pulsed coherent irradiation of GNRs needed results in irreversible deformation of GNRs, greatly reducing their two-photon luminescence (TPL) emission intensity. In this work we report the design, synthesis, and evaluation of mesoporous silica-encased gold nanorods (MS-GNRs) that incorporate photosensitizers (PSs) for two-photon-activated photodynamic therapy (TPA-PDT). The PSs, doped into the nano-channels of the mesoporous silica shell, can be efficiently excited via intra-particle plasmonic resonance energy transfer from the encased two-photon excited gold nanorod and further generates cytotoxic singlet oxygen for cancer eradication. In addition, due to the mechanical support provided by encapsulating mesoporous silica matrix against thermal deformation, the two-photon luminescence stability of GNRs was significantly improved; after 100 seconds of 800 nm repetitive laser pulse with the 30 times higher than average power for imaging acquisition, MS-GNR luminescence intensity exhibited ~260% better resistance to deformation than that of the uncoated gold nanorods. These results strongly suggest that MS-GNRs with embedded PSs might provide a promising photodynamic therapy for the treatment of deeply situated cancers via plasmonic resonance energy transfer.

Development of a laser-activated mesoporous silica nanocarrier delivery system for applications in molecular and genetic research

“…52 Additionally, gold nanostructures are known to irreversibly deform under even very lowenergy stimulus, resulting in a spectral shift of peak surface plasmon resonance absorption, thereby reducing the efficiency of any photon or laser-induced methods, and have also been shown to be cytotoxic in mammalian cells following laserinduced modifications. 49,53 In contrast, our present study investigated the use of MSNPs alone with IR laser treatment to increase the expression of MSNP cargo naturally via normal cellular machinery, illustrating that a heat-stimulus response can be achieved without the use of two-photon-activation using gold cores, which is highly desirable for investigations in the reproductive sciences.…”

“…For example, Volodkin et al 47 demonstrated that gold cores inside MSNP pores could be heated with NIR light to transfer heat to liposome bilayer cargo to release encapsulated dye molecules, while Mura et al 48 reported that an increase in temperature of NIR-treated gold nanoparticle cores caused a phase transition in polymers capping mesoporous silica shells, allowing leakage of a preloaded drug. Chen et al 49 further illustrated that mesoporous silica shells encapsulating gold nanorod cores provided mechanical support against thermal deformation following laser irradiation, compared to uncoated nanorods. While these reports used NIR treatment with mesoporous silica components, it was the gold particles that were responsible for thermoresponsiveness through plasmon resonance and two-photonactivated therapy of photosensitizers.…”

Beyond the Barriers of Light Penetration: Strategies, Perspectives and Possibilities for Photodynamic Therapy

“…Since TP excitation requires high incident laser intensity, the GNRs may undergo an irreversible deformation that leads to a loss of their emission properties. To prevent this type of photo-damage, Chen et al synthesized mesoporous silica-encased GNRs that incorporate a PS for TP activated PDT and showed efficient generation of 1 O 2 and cell killing 88. In addition to GNRs, QDs are potential candidates for TP mediated PS activation.…”

Photoluminescent nanoplatforms in biomedical applications

“…Au nanoparticles have also been employed to enhance the absorption of light of the PS by effect of the localized SPR. Chen et al investigated the enhanced fluorescence and ROS production of porphyrin PS molecules conjugated to silica-coated Au nanorods upon one-and two-photon excitation [165]. They attributed the observed enhancement to a combination of the local electric field amplification and increased radiative decay rates.…”

“…They attributed the observed enhancement to a combination of the local electric field amplification and increased radiative decay rates. As well, Föster Resonance Energy Transfer (FRET) has been proposed for the activation of PS to enhance the production of ROS [165,166]. Martynenko et al employed ZnSe/ZnS QDs as energy donors for chlorin-Ce6 PS molecules [167].…”