GIPO newsletter

The application of Plasmonic infrared thermal emitters in cancer therapy

Professor Si-Chen Lee

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

Infrared technologies have wide applications in silicon photonics, biotechnology, cancer therapy, night vision, communication and environmental protection. We developed narrow bandwidth plasmonic and waveguide thermal emitters achieved by Au/SiO₂/Au tri-layer structures. Manipulate the blackbody radiation spectra of the heated device to obtain a narrow bandwidth infrared light source by controlling the period or metal width of top metallic layer to select emission wavelength. Fig. 1(a) shows a typical metal-dielectric-metal structure. There are two major kinds of infrared thermal emitters, including plasmonic thermal emitter (PTE) and waveguide thermal emitter (WTE). The thermal emission spectra of PTE and WTE are shown in Fig.1(c)-(d), respectively. Furthermore, we demonstrate dual-wavelength LSP thermal emitters by using double tri-layer Au/SiO₂/Au structures with different SiO₂ thickness, as shown in Fig.1 (e). Fig. 1(f) shows the waveguide type dual-wavelength thermal emitters. We use a metallic grating embedded in the central dielectric layer of a waveguide thermal emitter as a beam splitter, dividing the device into two waveguide structures for TE and TM polarizations. We can use a polarizer to select the wavelength we need. Fig.2 shows the effect of MIR exposure on the actin filaments and focal adhesions of MDA-MB-231 breast cancer cells. We found that mid-infrared (3~5 μm region) exposure inhibited breast cancer cell proliferation, induced morphological changes by altering the cellular distribution of cytoskeletal components, as shown in Fig. 2(a)-(b). It has potential to be used in the breast cancer therapy in the future.

Fig. 1 (a) The scheme of MIM structure. (b) Dispersion diagram of PTE with SP and LSP modes. (c)(d) is the emission spectra of PTE and WTE. The emission spectra of (e) dual-wavelength LSP thermal emitters by using double tri-layer Au/SiO₂/Au structures with different SiO₂ thickness and (f) the waveguide type dual-wavelength thermal emitters with different polarizations.

Fig. 2. (a) Three breast cancer cells. (b) Effect of MIR exposure on the actin filaments and focal adhesions of MDA-MB-231 cells.

Extending resonant wavelengths of contour bowtie nano-antennas with fixed footprint size

Professor Hung-chun Chang

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

Properly designed plasmonic bowtie antennas (BAs) are known to produce “hot spots” in the antenna gap and have been extensively investigated in the visible and infrared wavelength range both theoretically and experimentally. The dependence of the field enhancement and confinement in the gap and the resonant wavelength, λ_res, on various parameters of the BA geometry has been widely studied. It has been known that λ_res is proportional to the antenna length. Several designs have been proposed to redshift the resonance of the nano-antenna over a wide wavelength range while maintaining the antenna size the same. A simple one proposed by Sederberg et al. [Opt. Express 19, 15532 (2011)] is contour bowtie antennas (CBAs) involving air holes with the antenna response tuned by varying the contour thickness. Fig. 1(a) depicts the three-dimensional (3D) structure of an isolated gold BA under a plane-wave illumination from the air side and Fig. 1(b) shows the gold contour of the CBA. In recent research, we have proposed a modified CBA (MCBA) structure, as shown in Fig. 1(c) to further red-shift the spectral response under the same CBA footprint size.

With our in-house developed 3D finite-difference time-domain (FDTD) method, we first simulated and compared the spectra of the conventional solid BA, the CBA, and our proposed MCBA. Referring to Figs. 1(a)–1(c), the gap area is 30 nm x 30 nm, the gold film thickness is d = 36 nm, the contour width is t = 30 nm, the relative permittivity of the silica substrate is 2.25, and the dielectric function of gold is described by the Drude model with ε_∞ = 1, ω_p = 11500 (THz), and γ_p = 92 (THz). Figure 1(d) shows the gap enhancement factor versus the wavelength for the solid BA (θ = 90°), the CBA (θ = 90°), and the MCBA with different flare angles θ from 110° to 170° with 20° increment. The original resonance of the solid BA occurs at λ_res = 1.34 μm, and its corresponding electric field enhancement in the gap is 22.5. For the CBA, λ_res redshifts to 2.22 μm and the field enhancement increases to 37.7. For the MCBA, a further redshift trend occurs with increasing θ. The resonance reaches to 2.66 μm as θ = 170°, and its corresponding field enhancement is 31.4, which is still better than that of BA. We are working on extending the resonant paths by utilizing the hollow spaces of the MCBA to further broaden the resonant spectral range under the same antenna footprint size. (Hui-Hsin Hsiao, Shian-Min Chiou, Yu-Ping Chang, and Hung-chun Chang, to appear in META’15 Abstracts.)

Figure 1 (a) The 3D structure of an isolated BA under a plane-wave illumination from the air side. (b) The schematic view of the BA. (b) That of the CBA. (c) That of the MCBA. (d) Gap enhancement spectra for the BA, the CBA (θ = 90°), and the MCBA (θ = 110°, 130°, 150°, 170°).

Cancer Cell Uptake Behavior of Au Nanoring and Its Localized Surface Plasmon Resonance Induced Cell Inactivation

Professor C. C. (Chih-Chung) Yang

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

Au nanorings (NRIs), which have the localized surface plasmon resonance (LSPR) wavelength around 1058 nm, either with or without linked antibodies, are applied to SAS oral cancer cells for cell inactivation through the LSPR-induced photothermal effect when they are illuminated by a laser of 1065 nm in wavelength. Different incubation times of cells with Au NRIs are considered for observing the variations of cell uptake efficiency of Au NRI and the threshold laser intensity for cell inactivation. In each case of incubation time, cell sample is washed for evaluating the total Au NRI number per cell adsorbed and internalized by the cells based on inductively coupled plasma mass spectrometry measurement. Also, the Au NRIs remaining on cell membrane are etched with KI/I₂ solution to evaluate the internalized Au NRI number per cell. The threshold laser intensities for cell inactivation before washout, after washout, and after KI/I₂ etching are calibrated from the circular area sizes of inactivated cells around the illuminated laser spot center with various laser power levels. By using Au NRIs with antibodies (NRI-AB), the internalized Au NRI number per cell increases monotonically with incubation time up to 24 hrs. However, the number of Au NRI remaining on cell membrane reaches a maximum at 12 hrs in incubation time. The cell uptake behavior of an Au NRI without antibodies (NRI-control) is similar to that with antibodies except that the uptake NRI number is significantly smaller and the incubation time for the maximum NRI number remaining on cell membrane is delayed to 20 hrs. By comparing the threshold laser intensities before and after KI/I₂ etching, it is found that the Au NRIs remaining on cell membrane cause more effective cancer cell inactivation, when compared with the internalized Au NRIs.

Fig. 1 Normalized extinction spectrum of the fabricated Au NRIs in PBS. The inset shows the SEM image of the Au NRIs before liftoff.

Fig. 2 (a)-(d): Microscopic images of cells after laser illumination with the laser powers of 230, 200, 200, and 180 mW, respectively, under the pre-washout condition when NRI-AB is applied to the cells and the incubation time is 16 hrs. (e)-(h) and (i)-(l): Corresponding microscopic images under the post-washout and after-etching conditions, respectively.

Fig. 3 Threshold laser intensities under the pre-washout, post-washout, and after-etching conditions for various incubation times when NRI-AB is applied to the cells.

Fig. 4 Threshold laser intensities similar to those in Fig.3 when NRI-control is applied to the cells.

Enhancements of the emission and light extraction of a radiating dipole coupled with localized surface plasmon induced on a surface metal nanoparticle in a light-emitting device

Professor Y. W. Kiang’s Laboratory

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

The radiated power enhancement and more congregated radiation of a radiating dipole within a GaN material when it is coupled with the localized surface plasmon (LSP) resonance modes induced on a surface Ag nanoparticle (NP) are numerically demonstrated. The numerical study is based on an algorithm including the induction of LSP resonance on the Ag NP by the source dipole and the feedback effect of the LSP resonance field on the source dipole behavior. The spectral peaks of radiated power enhancement correspond to the substrate LSP resonance modes with mode fields mainly distributed around the bottom of the Ag NP such that the coupling system radiates mainly into the GaN half-space. By moving the radiating dipole laterally away from the bottom of the Ag NP, the spectral peaks of radiated power enhancement red shift and their levels diminish with increasing lateral distance. The radiation patterns in the GaN half-space show more congregated radiation around the vertical direction, indicating that the light extraction efficiency can be enhanced in an LSP-coupled light-emitting device with surface metal NPs.

Fig. 1 Demonstration of the problem geometry, in which an Ag NP is placed on the surface of a thick GaN layer with an embedded thin QW layer at the depth of d. A radiating dipole, which is represented by a thick (red) arrow, is located in the QW layer.

Fig. 2 Normalized downward radiated powers of the NP-dipole coupling system as functions of wavelength for d = 30, 50, 70, 90, and 120 nm when the dipole is located exactly below the Ag NP, i.e., at x = 0. The Ag NP is surrounded by air in the upper-half-space. For comparison, the result in the case of no Ag NP at the air/GaN interface with d = 70 nm is also plotted as the dashed curve.

Ordering InGaP epilayer directly grown on Ge substrate

Professor Hao-Hsiung Lin

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

Ternary InGaP lattice-matched to GaAs has been well studied for decades and found applications to several important photonic and electronic devices, such as heterojunction bipolar transistors, laser diodes, and so on. Recently, the ternary has been deposited on Ge substrates as one of the subcell of the InGaP/InGaAs/Ge triple-junction tandem solar cells for high concentration photovoltaic. In this application, although the lattice constant of InGaP has been constrained to that of Ge substrate, one still can adjust the energy gap of InGaP by controlling the ordering of the ternary. The growth of the ternary semiconductor under certain conditions has a tendency towards atomic ordering due to the differences of the atomic size and the binding energy, which can spontaneously adopt a CuPt-type ordered structure. Fig. 1(a), indicates a good InGaP/Ge interface. Note that the miscut of the Ge substrate is towards direction. Steps resulting from the miscut are expected to be observed in the lattice image of the plane. However, as shown in Fig. 1(b), we did not observe the expected steps. The TED patterns with and zone axes are shown in Fig. 2(a) and (b), respectively. As can be seen, only superstructure spots … along direction are observed. For growth plane, there are four planes possible for Cu-Pt ordering. In Fig. 3(a), a sharp peak at 354 cm^-1 is observed. The peak has been previous reported in the literature, and was attributed to the trigonal cationic arrangement with LO symmetry. In order to understand the behavior of this mode, the normalized Raman spectra are plotted in Fig. 3(b). According to the C_3v selection rule, the 354 cm^-1 mode is only forbidden in configuration.

Fig. 1 High resolution cross-sectional TEM images of the InGaP/Ge interfaces. (a) on plane and (b) on plane.

Fig. 2 TED patterns of InGaP epilayer. (a) Zone axis is and (b) zone axis is .

Fig. 3 Room-temperature Raman spectra of the ordering InGaP with eight different polarization configurations. The eight configurations are , , , , , , and . (a) Full spectra with the eight configurations. The orientations of the polarizations are also shown in the inset. (b) Normalized spectra showing the peak at 354 cm^-1, which is relevant to the CuPt-B ordering phase.