A comparison of the surface nanostructure from two different types of gram-negative cells: Escherichia coli and Rhodobacter sphaeroides

Bacteria have been studied using different microscopy methods for many years. Recently, the developments of high-speed atomic force microscopy have opened the doors to study bacteria in new ways due to the fact that it uses much less force on the sample while imaging. This makes the high-speed atomic force microscope an indispensable technique for imaging the surface of living bacterial cells because it allows for the high-resolution visualization of surface proteins in their natural condition without disrupting the cell or the activity of the proteins. Previous work examining living cells of Magnetospirillum magneticum AMB-1 demonstrated that the surface of these bacteria was covered with a net-like structure that is mainly composed of porin molecules. However, it was unclear whether or not this feature was unique to other living bacteria. In this study we used the high-speed atomic force microscope to examine the surface of living cells of Escherichia coli and Rhodobacter sphaeroides to compare their structure with that of M. magneticum. Our research clearly demonstrated that both of these types of cells have an outer surface that is covered in a network of nanometer-sized holes similar to M. magneticum. The diameter of the holes was 8.0 ± 1.5 nm for E. coli and 6.6 ± 1.1 nm for R. sphaeroides. The results in this paper confirm that this type of outer surface structure exists in other types of bacteria and it is not unique to Magnetospirillum.     

Spiral MR fingerprinting at 7 T with simultaneous B1 estimation

Magnetic resonance fingerprinting is an efficient, new approach for quantitative imaging with MR. We aimed to extend this technique to cases with B1 + inhomogeneities within the imaging volume.Previous approaches have used abrupt changes in flip angles to estimate the B1 + field simultaneously with T1 and T2, using a Cartesian approach in a small-animal scanner at 4.7 T. Here, we evaluated whether a similar approach would be suitable for imaging human brains using spiral readouts with a 7 T scanner.We found that our modified scheme could significantly reduce the adverse effects of B1 + inhomogeneities even in extreme cases, reducing both the bias and the variance in T2 estimations by an order of magnitude when compared to literature methods. Acquisitions used less than 1.5 W/kg SAR and could be performed in 12 s per slice.In conclusion, our approach can be used to perform quantitative imaging of the brain at 7 T in a short time, simultaneously estimating the B1 + profile.     

Imaging of Norway spruce early somatic embryos with the ESEM,Cryo-SEM and laser scanning microscope

This article describes the surface structure of Norway spruce early somatic embryos (ESEs) as a typical culture with asynchronous development. The microstructure of extracellular matrix covering ESEs were observed using the environmental scanning electron microscope as a primary tool and using the scanning electron microscope with cryo attachment and laser electron microscope as a complementary tool allowing our results to be proven independently. The fresh samples were observed in conditions of the air environment of the environmental scanning electron microscope (ESEM) with the pressure from 550 Pa to 690 Pa and the low temperature of the sample from −18 °C to −22 °C. The samples were studied using two different types of detector to allow studying either the thin surface structure or material composition. The scanning electron microscope with cryo attachment was used for imaging frozen extracellular matrix microstructure with higher resolution. The combination of both electron microscopy methods was suitable for observation of “native” plant samples, allowing correct evaluation of our results, free of error and artifacts.     

Atomic resolution imaging of oxygen atoms close to heavy atoms by HRTEM and ED,using the superconductor SmFeAsO0.85F0.15 as an example

Imaging of light atoms has always been a challenge in high-resolution electron microscopy. Image resolution is mainly limited by lens aberrations, especially the spherical aberration of the objective lens. Image deconvolution could correct for the image distortion by lens aberrations and restore the structure projection, the resolution of which is limited by the information limit of the microscope. Electron diffraction unrestricted by lens aberrations could overcome this resolution limit. Here we show a combination of electron diffraction and image deconvolution to reveal simultaneously the atomic columns of O and considerably heavier Sm at a very close distance (1.17 Å) in iron-based superconductor SmFeAsO_0.85F_0.15 using a conventional 200 kV electron microscope. The approach used here, starting from an image and an electron diffraction pattern, has an advantage for those radiation-sensitive samples. Besides, it can be applied to simultaneously imaging light and heavy atoms, even though they have a big difference in atomic number and a much smaller atomic distance than the microscope resolution.     

Discrimination methods for biological contaminants in fresh-cut lettuce based on VNIR and NIR hyperspectral imaging

The rapid detection of biological contaminants such as worms in fresh-cut vegetables is necessary to improve the efficiency of visual inspections carried out by workers. Multispectral imaging algorithms were developed using visible-near-infrared (VNIR) and near-infrared (NIR) hyperspectral imaging (HSI) techniques to detect worms in fresh-cut lettuce. The optimal wavebands that can detect worms in fresh-cut lettuce were investigated for each type of HSI using one-way ANOVA. Worm-detection imaging algorithms for VNIR and NIR imaging exhibited prediction accuracies of 97.00% (RI_547/945) and 100.0% (RI_1064/1176, SI_1064-1176, RSI-I_{(1064-1173)/1064}, and RSI-II_{(1064-1176)/(1064+1176)})_, respectively. The two HSI techniques revealed that spectral images with a pixel size of 1 × 1 mm or 2 × 2 mm had the best classification accuracy for worms. The results demonstrate that hyperspectral reflectance imaging techniques have the potential to detect worms in fresh-cut lettuce. Future research relating to this work will focus on a real-time sorting system for lettuce that can simultaneously detect various defects such as browning, worms, and slugs.     

Chromatic aberration free liquid crystal adaptive optics for flood illuminated retinal camera

A high-resolution, flood-illumination retinal camera using liquid crystal (LC) adaptive optics (AO) is presented. The retinal camera uses light at 780 nm for ocular aberration measurement while light at 655 nm and 593 nm for retinal imaging. In order to avoid chromatic aberrations due to wavelength dependence of LC, we adopt an open-loop technique, in which dynamic correction of aberrations is applied only to the imaging light. A compensation pattern projected on the LC wavefront corrector is adjusted to provide phase wrapping of 2 π for illumination light. We confirmed feasibility of this technique by performing in vivo retinal imaging experiments. Photoreceptors were clearly revealed at both imaging light at 655 nm and 593 nm. Feasibility of the technique was also supported by comparison of the retinal images taken by the present open-loop technique with those taken by the conventional closed-loop one and by analysis of the spatial distribution of the photoreceptors.     

Modulation transfer function of QWIP and superlattice focal plane arrays

Modulation transfer function (MTF) is the ability of an imaging system to faithfully image a given object. The MTF of an imaging system quantifies the ability of the system to resolve or transfer spatial frequencies. In this paper we will discuss the detail MTF measurements of a 1024 × 1024 pixel multi-band quantum well infrared photodetector and 320 × 256 pixel long-wavelength InAs/GaSb superlattice infrared focal plane arrays.     

III–V on silicon: Observation of gallium phosphide anti-phase disorder by low-energy electron microscopy

The formation of anti-phase disorder is a major obstacle in the heteroepitaxy of III–V semiconductors on silicon. For an investigation of the anti-phase domain (APD) structure of GaP/Si(100) samples on mesoscopic length scales, we applied dark-field imaging in a low-energy electron microscope (LEEM) to thin GaP films grown on Si(100) substrates by metal organic vapor phase epitaxy (MOVPE). A contamination-free transfer of the samples from the MOVPE ambient to the ultra-high vacuum chamber of the microscope ensured that the atomically well-ordered, P-rich (2 × 2)/c(4 × 2) reconstruction of the surface was preserved. Mutually perpendicular oriented domains of the characteristic GaP(100) reconstruction identify the APDs in the GaP film at the surface and enabled us to achieve high contrast LEEM images. Striped patterns of APDs reflect the regular terrasse structure of the two-domain Si(100)(2 × 1) substrate far away from defects. APDs in the proximity of the defects have larger lateral extensions and are arranged in target pattern-like structures around the defects. In contrast to transmission electron microscopy, which was also applied in a specific dark-field mode for comparison, the characterization of anti-phase disorder by LEEM is non-destructive, does not require elaborate sample preparation, and addresses extended length scales.     

Resolution enhancement at a large convergence angle by a delta corrector with a CFEG in a low-accelerating-voltage STEM

Resolution reduction by a diffraction limit becomes severe with an increase in the wavelength of an electron at a relatively low accelerating voltage. For maintaining atomic resolution at a low accelerating voltage, a larger convergence angle with aberration correction is required. The developed aberration corrector, which compensates for higher-order aberration, can expand the uniform phase angle. Sub-angstrom imaging of a Ge [1 1 2] specimen with a narrow energy spread obtained by a cold field emission gun at 60 kV was performed using the aberration corrector. We achieved a resolution of 82 pm for a Ge–Ge dumbbell structure image by high angle annular dark-field imaging.     

Image quality of microns-thick specimens in the ultra-high voltage electron microscope

Image quality of MeV transmission electrons is an important factor for both observation and electron tomography of microns-thick specimens with the high voltage electron microscope (HVEM) and the ultra-HVEM. In this work, we have investigated image quality of a tilted thick specimen by experiment and analysis. In a 3 MV ultra-HVEM, we obtained transmission electron images in amplitude contrast of 100 nm gold particles on the top surface of a tilted 5 μm thick amorphous epoxy-resin film. From line profiles of the images, we then measured and evaluated image blurring, contrast, and the signal-to-noise ratio (SNR) under different effective thicknesses of the tilted specimen and accelerating voltages of electrons. The variation of imaging blurring was consistent with the analysis based on multiple elastic scattering. When the effective thickness almost tripled, image blurring increased from ～3 to ～20 nm at the accelerating voltage of 3 MV. For the increase of accelerating voltage from 1 to 3 MV in the condition of the 14.6 μm effective thickness, due to the reduction of multiple scattering effects, image blurring decreased from ～54 to ～20 nm, and image contrast and SNR were both obviously enhanced by a factor of ～3 to preferable values. The specimen thickness was shown to influence image quality more than the accelerating voltage. Moreover, improvement on image quality of thick specimens due to increasing the accelerating voltage would become less when it was further increased from 2 to 3 MV in this work.     

MR visible localization device for radiographic-pathologic correlation of surgical specimens

PurposeThe detection of small parenchymal hepatic lesions identified by preoperative imaging remains a challenge for traditional pathologic methods in large specimens. We developed a magnetic resonance imaging (MRI) compatible localization device for imaging of surgical specimens aimed to improve identification and localization of hepatic lesions ex vivo.Materials and methodsThe device consists of two stationary and one removable MR-visible grids lined with silicone gel, creating an orthogonal 3D matrix for lesion localization. To test the device, five specimens of swine liver with a random number of lesions created by microwave ablation were imaged on a 3 T MR scanner. Two readers independently evaluated lesion coordinates and size, which were then correlated with sectioning guided by MR imaging.ResultsAll lesions (n = 38) were detected at/very close to the expected localization. Inter-reader agreement of lesion localization was almost perfect (0.92). The lesion size estimated by MRI matched macroscopic lesion size in cut specimen (± 2 mm) in 34 and 35, respectively, out of 38 lesions.ConclusionUse of this MR compatible device for ex vivo imaging proved feasible for detection and three-dimensional localization of liver lesions, and has potential to play an important role in the ex vivo examination of surgical specimens in which pathologic correlation is clinically important.     

Classifying of Nellore cattle beef on Normal and DFD applying a non conventional technique

The aim of this study was to evaluate the accuracy in the Normal and DFD classification in Nellore beef using a bench-top hyperspectral imaging system. A hyperspectral imaging system (λ = 928–2524 nm) was used to collect hyperspectral images of the Longissimus thoracis et lumborum (n = 78) of Nellore cattle. The images were processed, being selected region of interest and extracted spectra image and were selected the wavelengths considered most important for the treats evaluated. Six linear discriminant models were developed to classify beef samples on Normal and DFD. The model using all wavelengths associated with the reflectance and absorbance spectrum transformed with the pretreatment 2nd derivative resulted in an overall accuracy of 93.6% for both pretreatments. In this configuration, the model was able to classify correctly 73 samples from a total of 78 samples. The results demonstrate that the hyperspectral imaging system may be considered a viable technology for beef classification on Normal and DFD.     

Femtosecond single-mode diode-pumped Cr:LiSAF laser mode-locked with single-walled carbon nanotubes

A low threshold Cr:LiSAF laser pumped with an inexpensive single-mode laser diode emitting 120 mW was passively mode-locked with a novel ultrafast saturable absorber mirror based on single-walled carbon nanotubes (SWCNT-SAM). Pulses as short as 122 fs were achieved, tunable across 14 nm. A second pump diode coupled in polarization allowed to shorten the pulse duration to 106 fs, with up to 24-mW output power.     

Preparation of micro-foils for TEM/STEM analysis from metallic powders

A technique has been developed which facilitates the preparation of electro-polished micro-foil transmission electron microscopy (TEM) specimens, which have previously been machined out of ≈100 μm diameter metallic powder particles using a Focussed Ion Beam (FIB) instrument. The technique can be used to create small volume TEM specimens from most metallic powder particles and bulk metal samples. This is especially useful when the matrices are ferritic steels, which are often difficult to image in the electron microscope, since the necessary aberration corrections change as the sample is tilted in the magnetic field of the objective lens.Small samples, such as powder particles, were attached to gold support grids using deposited platinum and were then ion milled to approximately 2 μm thickness in a focussed ion beam (FIB) instrument. Subsequently, the specimen assemblies were electropolished for short durations under standard conditions, to produce large (5 μm × 5 μm) electron transparent regions of material. The specimens produced by this technique were free from FIB related artefacts and facilitated atomic resolution scanning-TEM (STEM) imaging of ferritic and nickel matrices containing, for example, yttrium rich oxide nano-dispersoids.     

Wide-field imaging using a tunable terahertz free electron laser and a thermal image plate

The appearance of intense terahertz sources such as quantum cascade laser and free electron laser opens up new opportunities for 2D imaging. Though microbolometer and pyroelectric arrays are promising recorders, they are of small size and cannot be used when wide-field imaging in the longwave region is required. We applied for terahertz imaging 3″ × 3″ and 6″ × 6″ Macken Instruments Inc. “thermal image plates”, a set of thermal sensitive phosphor screens operating in a room temperature environment. The Novosibirsk free electron laser was used as a source of radiation. We have found that the response of thermal image plate is linear until the relative quenching is less than 60% of the initial luminescence intensity. The response curve follows the Seitz–Mott law. The threshold sensitivity was found to be 100 mW/cm² at 1.5 THz and 40 mW/cm² at 2.3 THz. Interferograms, holograms, and terahertz beam spatial distributions recorded in the spectral range of 1.2–2.5 THz are given as examples.     

18.2 nm Schwarzschild microscope for diagnostics of hot electron transport

Schwarzschild microscope at 18.2 nm for diagnostics of hot electron transport in femtosecond laser-plasma interaction has been developed. Based on the third-order aberration theory the microscope is designed for numerical aperture of 0.1 and magnification of 10. Mo/Si multilayer films with peak throughput at 18.2 nm is designed and deposited by magnetron sputtering method. The 24 lp/mm copper mesh is imaged via Schwarzschild microscope, and resolutions of less than 3 μm are measured in 1.2 mm field. The diagnostics experiment of hot electron transport is performed on 286 TW SILEX-I laser facilities, and the spatial distribution of radiation caused by hot electron is imaged by Schwarzschild microscope.     

Characterization of photonic nanojets in dielectric microdisks

The direct imaging of photonic nanojets in different dielectric microdisks illuminated by a laser source is reported. The SiO₂ and Si₃N₄ microdisks are of height 650 nm with diameters ranging from 3 μm to 8 μm. The finite-difference time-domain calculation is used to execute the numerical simulation for the photonic nanojets in the dielectric microdisks. The photonic nanojet measurements are performed with a scanning optical microscope system. The photonic nanojets with high intensity spots and low divergence are observed in the dielectric microdisks illuminated from the side with laser source of wavelengths 405 nm, 532 nm and 671 nm. The experimental results of key parameters are compared to the simulations and in agreement with theoretical results. Our studies show that photonic nanojets can be efficiently created by a dielectric microdisk and straightforwardly applied to nano-photonics circuit.     

Wettability,optical property of a superhydrophobic YAG film

A flame-like superhydrophobic yttrium aluminum garnet surface was obtained by a simple approach under ambient conditions. The influences of the concentration of curing agent and paraffin wax in course of the experiment were investigated. The as-prepared film shows superhydrophobicity which has a water contact angle of 158 ± 1.0°, and sliding angle of 4 ± 1.0°. Moreover, the water contact angle of the rough surface remained higher than 150°, after exposure for 10 days. Transmission electronic microscope, scanning electronic microscope, fluorescence spectrometer and atomic force microscope were also used to characterize the samples.     

Imaging quality analysis and evaluation of optical polarization imaging system with optical transfer matrix

An optical transfer matrix (OTM) is introduced and proposed to analyze the performance of optical polarization imaging systems. This 4 × 4 OTM describes the frequency transfer characteristics of the optical system for each Stokes parameter. It includes the transfer functions and the crosstalk functions. The transfer functions can be used to analyze the imaging quality of the system for each polarization component, while crosstalk functions indicate the polarization errors. We calculate the modulation transfer matrix as an example and numerically simulate the Stokes vector imaging for a polarization imaging system with a singlet and rotating polarization elements. The simulated imaging results show conformance with the analysis.     

Mid-wave QWIPs for the [3–4.2 μm] atmospheric window

We report two approaches using Quantum Well Infrared Photodetectors for detection in the [3–4.2 μm] atmospheric window. Taking advantage of the large band gap discontinuity we demonstrated a strained AlInAs/InGaAs heterostructure on InP. The optical coupling in this structure has been experimentally and numerically investigated. The results show that the coupling is mainly due to guided modes. The second approach is based on double barrier strained AlGaAs/AlAs/GaAs/InGaAs active layers on GaAs. The segregation of the elements III in these structures has been investigated using a transmission electron microscope. The results show a strong modification of the conduction band profile. We demonstrate peak wavelengths at 3.9 μm for the InP based detector and 4.0 μm for the GaAs based detector. We report a background limited peak detectivity (2π field of view, 300 K background) at 4.0 μm of about 2 × 10¹¹ cm Hz^1/2 W^?1 at 77 K, and 1.5 × 10¹¹ cm Hz^1/2 W^?1 at 100 K.