Two-photon Luminescence Intensity Research Articles

Rhenium disulfide nanosheets as a promising probe for intracellular two-photon luminescence imaging

Near-infrared (NIR) light-mediated two-photon microscopy has become a promising tool for early cancer therapy. However, exploring novel two-photon probe with high biocompatibility and high photostability to resist photobleaching, remains a key challenge for performing in vivo bioimaging. Herein, a novel two-photon luminescence (TPL) probe named two-dimensional rhenium disulfide (ReS2) nanosheets was firstly reported for performing intracellular bioimaging. Under the illumination of low power NIR femtosecond laser, the prepared ReS2 nanosheets exhibited strong NIR photon absorption, generating a strong TPL band at 640 nm. In addition, in vitro TPL imaging showed that, ReS2 nanosheets possessed excellent photostability, enabling to resist photobleaching. More importantly, ReS2 nanosheets functionalized by polyethylene glycol (PEG) showed negligible cytotoxicity, suitable to perform intracellular TPL imaging. With prolonged 6-hour incubation time, the TPL intensity of PEG-ReS2 nanosheets in three kinds of living cells such as esophageal cancer cells (KYSE150), pancreatic cancer cells (4T1) and HeLa cells, were significantly enhanced by almost 4, 11, and 17 times, respectively. In view of their photothermal effects, the PEG-ReS2 nanosheets could work as an excellent TPL probe for monitoring photothermal therapy and evaluating therapeutic outcomes. This study highlights great potential of PEG-ReS2 nanosheets as a TPL biosensor for intracellular optical imaging and cancer therapy.

Probing electron transport in plasmonic molecular junctions with two-photon luminescence spectroscopy

Abstract Plasmonic core–molecule–shell (CMS) nanojunctions provide a versatile platform for studying electron transport through conductive molecules under light excitation. In general, the impact of electron transport on the near-field response of CMS nanojunctions is more prominent than on the far-field property. In this work, we use two-photon luminescence (TPL) spectroscopy to probe the effect of electron transport on the plasmonic properties of gold CMS nanojunctions. Theoretical calculations show that the TPL response of such nanojunctions is closely related to the near-field enhancement inside the metal regions, and can be strongly affected by the electron transport through the embedded molecules. TPL excitation spectroscopy results for three CMS nanojunctions (0.7, 0.9 and 1.5 nm junction widths) reveal no perceivable contribution from their low-energy plasmon modes. This observation can be well explained by a quantum-corrected model, assuming significant conductance for the molecular layers and thus efficient charge transport through the junctions. Furthermore, we explore the charge transport mechanism by investigating the junction width dependent TPL intensity under a given excitation wavelength. Our study contributes to the field of molecular electronic plasmonics through opening up a new avenue for studying quantum charge transport in molecular junctions by non-linear optical spectroscopy.

Site-Selective, Two-Photon Plasmonic Nanofocusing on a Single Quantum Dot for Near-Room-Temperature Operation

Although the study of single quantum dot (QD) properties without the background noise and dephasing processes caused by surrounding carriers is a crucial issue, the spatial-selective excitation of a single QD is still challenging, due to the diffraction nature of light. Here, we demonstrate a deep subwavelength excitation of a single QD using two-photon plasmonic nanofocusing. Self-aligned plasmonic nanofocusing on a single QD was achieved using metal coated nanopyramid structures. The highly enhanced local electric field generated by the plasmonic nanofocusing gives rise to a large increase in the optical nonlinear effect (i.e., two-photon excitation). As a result of the enhanced field enhancement on the metal-pyramid hybrid structure, the two-photon luminescence intensity was enhanced by a factor of 5000, and the selective excitation of a single QD enabled us to observe InGaN QD emission at near room temperature, due to the large suppression of the background emission. Our approach opens promising persp...

A Two-Photon Luminescent Dye-Loaded Metal-Organic Framework for Physiological Temperature Sensing within Biological Windows.

Luminescent temperature sensing in biological windows is uniquely superior compared to traditional temperature sensing methods because the scattering and absorption by skin, tissue and blood is minimal. In this study, the two-photon luminescence from dyes loaded into a metal-organic framework was utilised to achieve physiological temperature sensing within two biological windows. A composite was prepared that can be excited at 1064 nm to emit at 650 nm, well within the two biological windows. The two-photon luminescence intensity at 650 nm has a linear relationship with temperature over the range 20 to 60 °C. In addition, the stability and quantum efficiency were significantly improved after loading into the MOF and, with high temperature resolution, excellent repeatability and low biological toxicity, measurements with this composite has great potential to be applied to physiological temperature sensing in cells or tissues.

Hybrid Theranostic Platform for Second Near-IR Window Light Triggered Selective Two-Photon Imaging and Photothermal Killing of Targeted Melanoma Cells.

Despite advances in the medical field, even in the 21st century cancer is one of the leading causes of death for men and women in the world. Since the second near-infrared (NIR) biological window light between 950 and 1350 nm offers highly efficient tissue penetration, the current article reports the development of hybrid theranostic platform using anti-GD2 antibody attached gold nanoparticle (GNP) conjugated, single-wall carbon nanotube (SWCNT) for second near-IR light triggered selective imaging and efficient photothermal therapy of human melanoma cancer cell. Reported results demonstrate that due to strong plasmon-coupling, two-photon luminescence (TPL) intensity from theranostic GNP attached SWCNT materials is 6 orders of magnitude higher than GNP or SWCNT alone. Experimental and FDTD simulation data indicate that the huge enhancement of TPL intensity is mainly due to strong resonance enhancement coupled with the stronger electric field enhancement. Due to plasmon coupling, the theranostic material serves as a local nanoantennae to enhance the photothermal capability via strong optical energy absorption. Reported data show that theranostic SWCNT can be used for selective two-photon imaging of melanoma UACC903 cell using 1100 nm light. Photothermal killing experiment with 1.0 W/cm(2) 980 nm laser light demonstrates that 100% of melanoma UACC903 cells can be killed using theranostic SWCNT bind melanoma cells after just 8 min of exposure. These results demonstrate that due to plasmon coupling, the theranostic GNP attached SWCNT material serves as a two-photon imaging and photothermal source for cancer cells in biological window II.

Multifunctional superparamagnetic nanoshells: combining two-photon luminescence imaging, surface-enhanced Raman scattering and magnetic separation.

With the increasing need for multi-purpose analysis in the biomedical field, traditional single diagnosis methods cannot meet the requirements. Therefore new multifunctional technologies and materials for the integration of sample collection, sensing and imaging are in great demand. Core-shell nanoparticles offer a unique platform to combine multifunctions in a single particle. In this work, we have constructed a novel type of core-shell superparamagnetic nanoshell (Fe₃O₄@SiO₂@Au), composed of a Fe₃O₄ cluster core, a thin Au shell and a SiO₂ layer in between. The obtained multifunctional nanoparticles combine the magnetic properties and plasmonic optical properties effectively, which were well investigated by a number of experimental characterization methods and theoretical simulations. We have demonstrated that Fe₃O₄@SiO₂@Au nanoparticles can be utilized for two-photon luminescence (TPL) imaging, near-infrared surface-enhanced Raman scattering (NIR SERS) and cell collection by magnetic separation. The TPL intensity could be further greatly enhanced through the plasmon coupling effect in the self-assembled nanoparticle chains, which were triggered by an external magnetic field. In addition, Fe₃O₄@SiO₂@Au nanoparticles may have great potential applications such as enhanced magnetic resonance imaging (MRI) and photo-thermotherapy. Successful combination of multifunctions including magnetic response, biosensing and bioimaging in single nanoparticles allows further manipulation, real-time tracking, and intracellular molecule analysis of live cells at a single-cell level.

Two-photon luminescence properties of gold nanorods

Gold nanorods can be internalized by macrophages (an important early cellular marker in atherosclerosis and cancer) and used as an imaging contrast agent for macrophage targeting. Objective of this study is to compare two-photon luminescence (TPL) properties of four aspect ratios of gold nanorods with surface plasmon resonance at 700, 756, 844 and 1060 nm respectively. TPL from single nanorods and Rhodamine 6G particles was measured using a laser-scanning TPL microscope. Nanorod TPL emission spectrum was recorded by a spectrometer. Quadratic dependence of luminescence intensity on excitation power (confirming a TPL process) was observed below a threshold (e.g., <1.6 mW), followed by photobleaching at higher power levels. Dependence of nanorod TPL intensity on excitation wavelength indicated that the two-photon action cross section (TPACS) is plasmon-enhanced. Largest TPACS of a single nanorod (12271 GM) was substantially larger than a single Rhodamine 6G particle (25 GM) at 760 nm excitation. Characteristics of nanorod TPL emission spectrum can be explained by plasmon-enhanced interband transition of gold. Comparison results of TPL brightness, TPACS and emission spectrum of nanorods can guide selection of optimal contrast agent for selected imaging applications.

Tailoring and imaging the plasmonic local density of states in crystalline nanoprisms

Surface plasmon (SP) technologies exploit the spectral and spatial properties of collective electronic oscillations in noble metals placed in an incident optical field. Yet the SP local density of states (LDOS), which rule the energy transducing phenomena between the SP and the electromagnetic field, is much less exploited. Here, we use two-photon luminescence (TPL) microscopy to reveal the SP-LDOS in thin single-crystalline triangular gold nanoprisms produced by a quantitative one-pot synthesis at room temperature. Variations of the polarization and the wavelength of the incident light redistribute the TPL intensity into two-dimensional plasmonic resonator patterns that are faithfully reproduced by theoretical simulations. We demonstrate that experimental TPL maps can be considered as the convolution of the SP-LDOS with the diffraction-limited Gaussian light beam. Finally, the SP modal distribution is tuned by the spatial coupling of nanoprisms, thus allowing a new modal design of plasmonic information processing devices.

Solution-dispersible Au nanocube dimers with greatly enhanced two-photon luminescence and SERS

We report the synthesis of 43-nm diameter Au nanocube dimers by using Ag(+) ions as competitive ligands to freeze L-cysteine-induced assembly process of the nanocubes to a desirable stage. Ascribed to the resonant interparticle coupling with an newly arising plasmon band at 710 nm and local field enhancement, the two-photon luminescence intensity of the Au nanocube dimers in solution was over 20 times stronger than that of the monomers in the wavelength range 555-620 nm. Furthermore, by coupling Raman tags onto the nanocube surface, a solution-based surface-enhanced Raman scattering (SERS) of the nanocube dimers had an enhancement factor of over 10 times compared to the isolated nanocubes. To sum up, with high stability in solution and attractive optical properties, the Au nanocube dimers have potential applications in in vivo bio-imaging and solution-based SERS.

Spatially Modulated Two-Photon Luminescence from Si−Au Core−Shell Nanowires

Si−Au core−shell nanowires were synthesized with a two-step strategy combining chemical vapor deposition and wet chemistry methods. Si core diameter, Au shell thickness, and wire length were controlled during synthesis. Under a far-field two-photon excitation scanning microscope, spatially modulated two-photon luminescence (TPL) was observed from the core−shell nanowires prepared with several micrometers in length. The mode spacing scales linearly with the length of nanowires for samples with 15 and 40 nm Au shells. The spatial modulation pattern was found to be independent of the excitation wavelength. The TPL intensity displayed a cos2 dependence on the excitation field polarization, indicating a sequential two-photon excitation process enhanced by the longitudinal plasmon field. The spatially modulated TPL is interpreted by a standing wave model of surface plasmon polaritons along the core−shell nanowire which acts as a Fabry−Perot resonator. These results suggest TPL imaging of Si−Au core−shell nanowi...

Photoinduced phase transition in strongly correlated TTTA crystals probed with two-photon luminescence

Two-photon processes are used for studying photoinduced phase transition (PIPT) from diamagnetic low-temperature phase to paramagnetic high-temperature phase in strongly correlated organic radical 1,3,5-trithia-2,4,6-triazapentalenyl (TTTA) crystals. We have measured the Raman and luminescence spectra in the low-temperature phase after two-photon excitation with various excitation photon densities. After correction of re-absorption of the luminescence, the shape of the two-photon luminescence spectrum is in good agreement with that of the one-photon luminescence spectrum, which strongly suggests that the initial states of the two-photon luminescence are the same as those of the one-photon luminescence and are self-trapped excitons (STEs). As increasing the excitation photon density, PIPT to the high-temperature phase takes place with a threshold behavior as a sudden decrease of the two-photon luminescence intensity. This result suggests that STEs are the precursors of the PIPT and the two-photon luminescence can be a useful probe of whole PIPT dynamics from the microscopic lattice distortion to the macroscopic phase transition.

Two-Photon Luminescence Imaging of Cancer Cells Using Molecularly Targeted Gold Nanorods

We demonstrate the use of gold nanorods as bright contrast agents for two-photon luminescence (TPL) imaging of cancer cells in a three-dimensional tissue phantom down to 75 mum deep. The TPL intensity from gold-nanorod-labeled cancer cells is 3 orders of magnitude brighter than the two-photon autofluorescence (TPAF) emission intensity from unlabeled cancer cells at 760 nm excitation light. Their strong signal, resistance to photobleaching, chemical stability, ease of synthesis, simplicity of conjugation chemistry, and biocompatibility make gold nanorods an attractive contrast agent for two-photon imaging of epithelial cancer.

Photochromism and two-photon luminescence of Ag-TiO_2 granular composite films activated by near infrared ps/fs pulses

We reported photochromism and largely enhanced visible two-photon luminescence (TPL) of Ag-TiO(2) granular composite films by using ps/fs laser at the wavelength of 800 nm. Three types of photochromism spectra were observed when the Ag atom fraction are less than, comparable to and larger than the percolation threshold. The strong surface-plasmon-resonance enhanced visible TPL emissions near Ag(2)O transition band from the photoactivated Ag-TiO(2) samples were also observed. Furthermore, we found that the TPL intensity saturatedly increased while the absorbance at 800 nm exponentially decreased with the same rate as the increasing of photoactivation time, which means that both photochromism and TPL of Ag-TiO(2) composite films are originated from the photo-oxidation of Ag to Ag(+). These observations exhibit the multifunctional features of Ag nanoparticle materials.