Single-shot differential phase contrast microscopy using ring-shaped polarisation multiplexing illumination.

We propose a differential phase contrast microscopy that enables single-shot phase imaging for unstained biological samples. The proposed approach employs a ring-shaped LED array for polarisation multiplexing illumination and a polarisation camera for image acquisition. As such, multiple images of different polarisation angles can be simultaneously captured with a single shot. Through polarisation demultiplexing, the sample phase can therefore be recovered from the single-shot measurement. Both simulations and experiments demonstrate the effectiveness of the approach. We also demonstrate that ring-shaped illumination enables higher contrast and lower-distortion imaging results than disk-shaped illumination does. The proposed single-shot approach potentially enables phase contrast imaging for live cell samples in vitro. Lay Description: We propose a microscopy that enables imaging of transparent samples, unstained cells, etc. We demonstrate that the proposed method enables higher contrast and lower-distortion imaging results than conventional methods, and significantly improves imaging efficiency. The proposed method potentially enables dynamic imaging for live cell samples in vitro.

Contrast-enhanced, single-shot LED array microscopy based on Fourier ptychographic algorithm and deep learning.

LED array microscopes have the advantages of miniaturisation and low cost. It has been demonstrated that LED array microscopes outperform Köhler illumination microscopes in some applications. A LED array allows for a large numerical aperture of illumination. The larger numerical aperture of illumination brings the higher spatial resolution, but the lower image contrast as well. Therefore, there is a tradeoff between resolution and contrast for LED array microscopes. The Fourier ptychographic algorithm can overcome this tradeoff by increasing image contrast without sacrificing spatial resolution. However, the Fourier ptychographic algorithm requires acquisition of multiple images, which is time-consuming and results in live sample imaging challenging. To solve this problem, we develop contrast-enhanced, single-shot LED array microscopy based on the Fourier ptychographic algorithm and deep learning. The sample to be imaged is under illumination by all LEDs of the array simultaneously. The image captured is fed to several trained convolutional neural networks to generate the same number of images that are required by the Fourier ptychographic algorithm. We experimentally present that the image contrast of the final reconstruction is remarkably improved in comparison with the image captured. The proposed method can also produce chromatic-aberration-free results, even when an objective without aberration correction is used. We believe the method might provide live sample imaging with a low-cost approach.

Image-free classification of fast-moving objects using "learned" structured illumination and single-pixel detection.

Object classification generally relies on image acquisition and subsequent analysis. Real-time classification of fast-moving objects is a challenging task. Here we propose an approach for real-time classification of fast-moving objects without image acquisition. The key to the approach is to use structured illumination and single-pixel detection to acquire the object features directly. A convolutional neural network (CNN) is trained to learn the object features. The "learned" object features are then used as structured patterns for structured illumination. Object classification can be achieved by picking up the resulting light signals by a single-pixel detector and feeding the single-pixel measurements to the trained CNN. In our experiments, we show that accurate and real-time classification of fast-moving objects can be achieved. Potential applications of the proposed approach include rapid classification of flowing cells, assembly-line inspection, and aircraft classification in defense applications. Benefiting from the use of a single-pixel detector, the approach might be applicable for hidden moving object classification.

Full-color light-field microscopy via single-pixel imaging.

Light-field microscopy is a scanless volumetric imaging technique. Conventional color light microscope employs a micro-lens array at the image plane and samples the spatial, angular, and color information by a pixelated two-dimensional (2D) sensor (such as CCD). However, the space bandwidth product of the pixelated 2D sensor is a fixed value determined by its parameters, leading to the trade-offs between the spatial, angular, and color resolutions. In addition, the inherent chromatic aberration of the micro-lens array also reduces the viewing quality. Here we propose full-color light-field microscopy via single-pixel imaging that can distribute the sampling tasks of the spatial, angular, and color information to both illumination and detection sides, rather than condense on the detection side. Therefore, the space bandwidth product of the light-field microscope is increased and the spatial resolution of the reconstructed light-field can be improved. In addition, the proposed method can reconstruct full-color light-field without using a micro-lens array, thereby the chromatic aberration induced by the micro-lens array is avoided. Because distributing the three sampling tasks to both the illumination and detection sides has different possible sampling schemes, we present two sampling schemes and compare their advantages and disadvantages via several experiments. Our work provides insight for developing a high-resolution full-color light-field microscope. It may find potential applications in the biomedical and material sciences.

Reflection light-field microscope with a digitally tunable aperture by single-pixel imaging.

Reflected light microscope is a tool for imaging opaque specimens. However, most of the existing reflected light microscopes can only obtain the two-dimensional image of the specimen. Here we demonstrate that with the help of single-pixel imaging, we can develop a reflection light-field microscopy for volumetric imaging. Importantly, using single-pixel imaging, we can digitally adjust the size of the aperture diaphragm of the proposed reflection light-field microscope for changing the depth of field and for achieving three-dimensional differential phase-contrast imaging in an arbitrary direction, without a hardware change. Our approach may benefit various reflective specimens with wide depth information in the semiconductor industry and material science.

Spatially-incoherent annular illumination microscopy for bright-field optical sectioning.

Numerous advanced microscopic imaging techniques have been proposed for optical sectioning, but they generally employ a complex and costly optical system. Here we report a microscopy termed spatially-incoherent annular illumination microscopy (SAIM). It allows for simple, effective, non-fluorescence, and bright-field optical sectioning. The proposed technique is implemented by installing an annular array of light emitting diodes (LEDs) on a standard bright-field microscope for illumination. The LED array produces distinctive illumination, that is, each LED provides coherent, large-angle oblique illumination while all LEDs generate spatially-incoherent annular illumination. Such a distinctive illumination can improve both lateral resolution and axial resolution. The improvement of lateral resolution is due to the coherent and large-angle oblique illumination. The spatially-incoherent annular illumination can improve the axial resolution. It is because, for defocused structures, each LED results in a blurred image with a different lateral shift and all LEDs result in an incoherent stagger superposition of the defocused images. The superposition looks much more blurred, which improves the contrast of the in-focus image remarkably. We experimentally demonstrate that SAIM is able to provide bright-field optical sections with 600-nm axial resolution and 150-nm lateral half-pitch resolution by using a 525-nm wavelength LED array and an objective with 100X, numerical aperture (NA) 1.25.

Secured single-pixel broadcast imaging.

Active single-pixel imaging (also known as illumination-modulated single-pixel imaging) employs a spatial light modulator to illuminate a scene with structured patterns. The scheme of active single-pixel imaging is similar to a wireless broadcast system, allowing that multiple receivers use a single-pixel detector to capture an image simultaneously from a different place. The use of basis patterns allows for high-quality reconstructions and an efficient sampling process, but the public knowledge of the basis patterns is not a favorable feature for security applications. In order to develop a secured broadcast single-pixel imaging system, we propose to employ block-permutated Hadamard basis patterns for illumination. The randomness in permutation operations introduces strong security characteristics for the system. Both simulation and experimental results demonstrate our proposed scheme has satisfactory imaging quality and efficiency. This work generates a new insight for the application of single-pixel imaging and provides a solution for developing a secured imaging system for non-visible wavebands.

Micro-tomography via single-pixel imaging.

Tomographic imaging allows for the cross-sectional imaging of specimen, whereas single-pixel imaging can produce image only with a spatial non-resolved detector. Here we propose a compact tomographic imaging system combining single-pixel imaging. This approach uses a digital micromirror device (DMD) to encode the spatial information of specimen and employs an array of single-pixel detectors to record the light signals from different directions. For each single-pixel detector, we can retrieve an image of the specimen from a unique perspective angle. Based on the retrieved images, we can realize tomographic imaging, such as intensity images refocusing and three-dimensional (3D) differential-phase-contrast imaging, without mechanically scanning the specimen. Experimental results also demonstrate that the micro-tomographic images with 384×384 pixels can be simultaneously realized only with an array of 5×6 single-pixel detectors. Furthermore, due to the broad operational spectrum of the single-pixel detector, the proposed method is a good candidate to realize tomographic imaging with the non-visible light wavebands, such as terahertz and x-ray, thus it would open up opportunities in many life science and engineering fields.

Overexpression of the halophyte Kalidium foliatum H⁺-pyrophosphatase gene confers salt and drought tolerance in Arabidopsis thaliana.

According to sequences of H(+)-pyrophosphatase genes from GenBank, a new H(+)-pyrophosphatase gene (KfVP1) from the halophyte Kalidium foliatum, a very salt-tolerant shrub that is highly succulent, was obtained by using reverse transcription PCR and rapid amplification of cDNA ends methods. The obtained KfVP1 cDNA contained a 2295 bp ORF and a 242 bp 3'-untranslated region. It encoded 764 amino acids with a calculated molecular mass of 79.78 kDa. The deduced amino acid sequence showed high identity to those of H(+)-PPase of some Chenopodiaceae plant species. Semi-quantitative PCR results revealed that transcription of KfVP1 in K. foliatum was induced by NaCl, ABA and PEG stress. Transgenic lines of A. thaliana with 35S::KfVP1 were generated. Three transgenic lines grew more vigorous than the wild type (ecotype Col-0) under salt and drought stress. Moreover, the transgenic plants accumulated more Na(+) in the leaves compared to wild type plants. These results demonstrated that KfVP1 from K. foliatum may be a functional tonoplast H(+)-pyrophosphatase in contributing to salt and drought tolerance.