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Photonics, Volume 4, Issue 3 (September 2017) – 5 articles

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2144 KiB

Open AccessArticle

Design Rules For a Nano-Opto-Mechanical Actuator Based on Suspended Slot Waveguides

by Francesco De Leonardis, Martino De Carlo and Vittorio M. N. Passaro

Photonics 2017, 4(3), 43; https://doi.org/10.3390/photonics4030043 - 1 Sep 2017

Cited by 6 | Viewed by 4875

Abstract

In this paper, physical modeling including optical and Casimir forces is adopted in order to analyze a nano-opto-mechanical actuator based on silicon-on-insulator suspended slot waveguides. Numerical simulations based on the finite element method and systematic design rules are presented. Moreover, parametric investigations on [...] Read more.

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1359 KiB

Open AccessArticle

Totally Vacuum-Free Processed Crystalline Silicon Solar Cells over 17.5% Conversion Efficiency

by Abdullah Uzum, Hiroyuki Kanda, Hidehito Fukui, Taichiro Izumi, Tomitaro Harada and Seigo Ito

Photonics 2017, 4(3), 42; https://doi.org/10.3390/photonics4030042 - 26 Aug 2017

Cited by 7 | Viewed by 5494

Abstract

In this work, we introduce a totally vacuum-free cost-efficient crystalline silicon solar cells. Solar cells were fabricated based on low-cost techniques including spin coating, spray pyrolysis, and screen-printing. A best efficiency of 17.51% was achieved by non-vacuum process with a basic structure of <AI/p+/p−Si/n+/SiO₂/TiO₂/Ag> CZ-Si p-type solar cells. Short circuit current density (J_SC) and open circuit voltage (V_OC) of the best cell were measured as 38.1 mA·cm⁻² and 596.2 mV, respectively with fill factor (FF) of 77.1%. Suns-Voc measurements were carried out and the detrimental effect of the series resistance on the performance was revealed. It is concluded that higher efficiencies are achievable by the improvements of the contacts and by utilizing good quality starting wafers. Full article

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Figure 1
Schematics of solar cell structures fabricated with non-vacuum process techniques with various surface structures and with various ARC films, (a) <AI/p+/p−Si/n+/Ag> with flat surface, (b) <AI/p+/p−Si/n+/Ag> with textured surface, (c) <AI/p+/p−Si/n+/TiO2/AI2O3/Ag> with flat surface, (d) <AI/p+/p−Si/n+/TiO2/AI2O3/Ag> with textured surface, (e) <AI/p+/p−Si/n+/TiO2/Ag> with textured surface, (f) <AI/p+/p−Si/n+/TiO2/ZrO2/Ag> with textured surface, (g) <AI/p+/p−Si/n+/SiO2/TiO2/Ag> with textured surface. Full article ">Figure 2
I–V curve of the fabricated solar cells by each vacuum-less process. Full article ">Figure 3
Measured I–V curve of the best cell compared with the pseudo I–V curve measured by Suns-Voc. Full article ">

3570 KiB

Open AccessArticle

Exploring the Potential of Airyscan Microscopy for Live Cell Imaging

by Kseniya Korobchevskaya, B. Christoffer Lagerholm, Huw Colin-York and Marco Fritzsche

Photonics 2017, 4(3), 41; https://doi.org/10.3390/photonics4030041 - 7 Jul 2017

Cited by 63 | Viewed by 27070

Abstract

Biological research increasingly demands the use of non-invasive and ultra-sensitive imaging techniques. The Airyscan technology was recently developed to bridge the gap between conventional confocal and super-resolution microscopy. This technique combines confocal imaging with a 0.2 Airy Unit pinhole, deconvolution and the pixel-reassignment principle in order to enhance both the spatial resolution and signal-to-noise-ratio without increasing the excitation power and acquisition time. Here, we present a detailed study evaluating the performance of Airyscan as compared to confocal microscopy by imaging a variety of reference samples and biological specimens with different acquisition and processing parameters. We found that the processed Airyscan images at default deconvolution settings have a spatial resolution similar to that of conventional confocal imaging with a pinhole setting of 0.2 Airy Units, but with a significantly improved signal-to-noise-ratio. Further gains in the spatial resolution could be achieved by the use of enhanced deconvolution filter settings, but at a steady loss in the signal-to-noise ratio, which at more extreme settings resulted in significant data loss and image distortion. Full article

(This article belongs to the Special Issue Superresolution Optical Microscopy)

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Figure 1
Airyscan microscope principle and configuration: (a) scheme of confocal and Airyscan detection paths; (b) 32 detection element arrangement in the Airyscan detector design; (c) representative images of a 200-nm TetraSpeck fluorescent bead aggregate acquired at 488-nm excitation for all four conditions: confocal 0.2 AU; Channel 1 of Airyscan detector; sum of the 32 channels of Airyscan detector; and Airyscan processed. Scale bar is 1 μm. Full article ">Figure 2
Quantitative evaluation of the lateral spatial resolution by imaging fluorescent beads. (a) Representative images of the 23-nm fluorescent GATTA-Beads (OG488) in the lateral (left panel) and axial direction (right; corresponding projections along the line indicated with white triangles) acquired at 488-nm excitation, displaying all four imaging conditions: confocal using a pinhole diameter of 0.2 AU and Airyscan processed with AF4, AF6 and AF8. Scale bar is 1 μm. (b) Graph showing that the FWHM of the PSF for Atto647N GATTA-Beads imaged at 633 nm for the reconstructed Airy Sum image (open circle) and the image from Channel 1 of the Airyscan detector (open diamond) are closely equivalent to confocal images at 1 AU (open triangle) and 0.2 AU (open square), respectively. The graph further shows the strong dependence of the FWHM of the PSF on the strength of the automatically-determined default Wiener filter setting (blue diamonds) relative to the much weaker dependence (orange box) on the image acquisition settings in terms of either the excitation power (orange triangle, green diamond) or the use of line averaging (red circle, pink triangle). (c) Graph showing the FWHM of PSF vs. Airyscan filter strengths for 200 nm TetraSpeck beads (open points) imaged at different excitation powers 2, 4, 6 and 8% laser power (red, blue, black and green dots and line, respectively) and 23-nm GATTA-Beads acquired at 633-nm (black) and 488-nm (purple) excitation with 2% excitation power. Orange boxes indicate default AF settings. Full article ">Figure 3
Qualitative evaluation of the lateral spatial resolution of Argo-SIM slide using 488-nm excitation. (a,b) Representative images of focal plane of z-stack image set of the lateral resolution test pattern on an Argo-SIM slide containing central pairs of lines with spacing gradually increased from 0 to 390 nm in steps of 30 nm from left to right. Scale bar in is 1 μm. (a) Conventional confocal image with pinhole setting of 1 Airyscan Unit (AU); and (b) processed Airyscan data at the default Airyscan Filtering (AF5.9). (c–f) ROIs (red rectangles) from (a,b) of the test pattern with specified central line spacing from left to right of 60, 90, 120, 150 and 180 nm and representative intensity line profiles from rectangular ROIs (green rectangles) with a line height of 10 pixels. (c) ROI and representative intensity line profile for confocal image at 1 AU. (d) ROI and representative intensity line profile for raw Airyscan data from Channel 1. (f) ROI and representative intensity line profile from the reconstructed sum of the raw Airyscan data. (f–j) ROIs and representative intensity line profiles for processed Airyscan data at the default Wiener filter setting of 5.9; (e) Airy sum: the sum of all 32 channels (f); and at increased Wiener filter settings of 6.5 (g), 7.0 (h), 8.0 (i) and 9.0 (j). Representative intensity line profiles in (c–j) are ROIs (blue rectangles) emphasizing the increased noise level in the case of the data from Channel 1 of the Airyscan detector only (d); and successive increase if noise level with increasing Wiener filter setting (f–j) as is also apparent in the image data in (d) and (f–j). Full article ">Figure 4
Quantitative evaluation of lateral spatial resolution by imaging of the Argo-SIM slide. (a) Results from the analysis relative intensity drop, ΔI/Ipeak, for all four imaging conditions and increasing AFs as shown in <a href="#photonics-04-00041-f003" class="html-fig">Figure 3</a>. Error bars are standard error of the mean. Also shown is the condition for the size of the intensity dip for the Rayleigh criteria for a circular aperture of ΔI/Ipeak ≈ 0.265. (b) Quantitative analysis of the SNR for all four imaging conditions and increasing AFs as shown in <a href="#photonics-04-00041-f003" class="html-fig">Figure 3</a>. Error bars are the standard error of the mean. Full article ">Figure 5
Quantitative evaluation of lateral spatial resolution in biological specimen. (a) Representative image of Airy scan processed (AF6) nuclear pores complexes in fixed HeLa cell labelled by an antibody to Nup153. Scale bar is 5 μm. (b) Mean FWHM of individual NPC vs. different strengths of the Wiener filter in the reconstruction of the processed Airy scan image. The orange area shows the default filter settings; the red line shows the value for confocal 0.2 AU with the error bar (standard deviation, pink). (c) Direct comparison of the Region of Interest area (ROI; red rectangle in (a)) between confocal 0.2 AU and Airy processed images with Wiener Filters 4, 6 and 8, respectively. Scale bar is 1 μm. Full article ">Figure 6
Time-lapse images of activating Rat Basophilic Leukaemia (RBL) cell. (a) Comparison of 1.25 AU confocal and Airyscan processed AF6.7 images. Scale bar is 10 μm. (b) Direct comparison of Region of Interest area (ROI; red rectangle in (a)) between confocal 1.25 AU and Airy processed images with AF4, AF6 and AF7, respectively. Scale bar is 5 μm. (c) Time-lapse of activating RBL cell at 0, 60 and 120 s, respectively. Green LifeAct-citrine (excitation at 488 nm), red SNAP-tag (excitation at 561 nm). (d) Intensity profiles from 1.25 AU (grey filled), AF7 (blue dots) and AF8 (red) images along the line indicated by white arrows in (b). Arrows indicate peaks from two separate actin fibres, which are only distinguishable at high AF strength and are not resolved at 1.25 AU. Full article ">

1556 KiB

Open AccessArticle

Mapping Molecular Function to Biological Nanostructure: Combining Structured Illumination Microscopy with Fluorescence Lifetime Imaging (SIM + FLIM)

by Frederik Görlitz, David S. Corcoran, Edwin A. Garcia Castano, Birgit Leitinger, Mark A. A. Neil, Christopher Dunsby and Paul M. W. French

Photonics 2017, 4(3), 40; https://doi.org/10.3390/photonics4030040 - 7 Jul 2017

Cited by 14 | Viewed by 6522

Abstract

We present a new microscope integrating super-resolved imaging using structured illumination microscopy (SIM) with wide-field optically sectioned fluorescence lifetime imaging (FLIM) to provide optical mapping of molecular function and its correlation with biological nanostructure below the conventional diffraction limit. We illustrate this SIM + FLIM capability to map FRET readouts applied to the aggregation of discoidin domain receptor 1 (DDR1) in Cos 7 cells following ligand stimulation and to the compaction of DNA during the cell cycle. Full article

(This article belongs to the Special Issue Superresolution Optical Microscopy)

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Figure 1
Experimental configuration for SIM and FLIM applied to the same field of view. Full article ">Figure 2
Fluorescence intensity and intensity-weighted lifetime images of the DDR1 receptor expressed in Cos7 cells and labelled stochastically with SNAP-tag-Alexa-488 or SNAP-tag-Alexa-546 and stimulated with collagen. (a,b) shows the SIM images of Alexa-488 (a) and Alexa-546 (b) labelled DDR1 receptors while (c) shows the optically sectioned Alexa488 fluorescence lifetime map and (d) shows the corresponding intensity-weighted fluorescence lifetime image. (e) shows the intensity-weighted Alexa488 fluorescence lifetime image added to the SIM intensity image of (a) and (f–h) presents sub-regions of (e) magnified to show nanostructure with corresponding intensity-weighted lifetime histograms and the intensity-weighted mean fluorescence lifetime values inset (STD can be found in <a href="#photonics-04-00040-t001" class="html-table">Table 1</a>). (Scale bar: 6 µm). Full article ">Figure 3
SIM and intensity-weighted fluorescence lifetime images of NIH3T3 cells incorporating EdU that has been stochastically labelled with Alexa 594 or Alexa 647 using click-chemistry. (a–e) and (f–j) show cells in S-phase with different degrees of chromatin compaction. (a,f) show the Alexa594 SIM images, (b,g) show the intensity-weighted Alexa594 fluorescence lifetime images, (c,h) show the SIM + FLIM images, (d,i) show the corresponding intensity-weighted fluorescence lifetime histograms with intensity-weighted mean lifetime values inset (STD can be found in <a href="#photonics-04-00040-t001" class="html-table">Table 1</a>), and (e,j) show 2D histograms of Alexa594 intensity versus lifetime. (Scale bar: 6 µm). Full article ">

1127 KiB

Open AccessArticle

Phase Mask-Based Multimodal Superresolution Microscopy

by Ryan Beams, Jeremiah W. Woodcock, Jeffrey W. Gilman and Stephan J. Stranick

Photonics 2017, 4(3), 39; https://doi.org/10.3390/photonics4030039 - 6 Jul 2017

Cited by 10 | Viewed by 6225

Abstract

We demonstrate a multimodal superresolution microscopy technique based on a phase masked excitation beam in combination with spatially filtered detection. The theoretical foundation for calculating the focus from a non-paraxial beam with an arbitrary azimuthally symmetric phase mask is presented for linear and two-photon excitation processes as well as the theoretical resolution limitations. Experimentally this technique is demonstrated using two-photon luminescence from 80 nm gold particle as well as two-photon fluorescence lifetime imaging of fluorescent polystyrene beads. Finally to illustrate the versatility of this technique we acquire two-photon fluorescence lifetime, two-photon luminescence, and second harmonic images of a mixture of fluorescent molecules and 80 nm gold particles with <120 nm resolution (

λ

/7). Since this approach exclusively relies on engineering the excitation and collection volumes, it is suitable for a wide range of scanning-based microscopies. Full article

(This article belongs to the Special Issue Superresolution Optical Microscopy)

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