De-blurring Images of Living Biological Samples

December 10, 2018|

Imaging fast moving samples such as living biological samples is challenging because the images can appear blurred if the strobe light is not fast enough. This is an issue for high-quality quantitative phase imaging, which was too slow for many samples (image on right). STROBE faculty Laura Waller from Berkeley led a team to develop a new approach to reduce this blur, that enhances the speed to match the frame rate of the detector, to enable much clearer imaging of many biological systems (image on left).

M. Chen et al., "Quantitative differential phase contrast (DPC) microscopy with computational aberration correction," Optics Express 26, 32888-32899 (2018).

Correlative 3D X-ray Fluorescence and Ptychographic Tomography of Frozen-hydrated Green Algae

November 2, 2018|

A STROBE team led by Prof. Miao, in collaboration with Argonne National Laboratory, implemented hybrid 3D X-ray microscopy by combining cryogenic hard X-ray ptychography and X-ray fluorescence microscopy. Here, STROBE’s advanced GENFIRE tomography algorithm was used to correlate high resolution ultrastructure mapping and elemental distributions in an unlabeled, frozen-hydrated green algae.

J. Deng et al., “Correlative 3D x-ray fluorescence and ptychographic tomography of frozen-hydrated green algae”, Science Advances 4, eaau4548 (2018).

Electron Imaging Reveals the Conductance Watershed Between Two Electrodes

October 29, 2018|

Traditional transmission electron microscopy (TEM) excels at determining the physical structure of a sample, but reveals little about the electronic structure. STROBE faculty Chris Regan at UCLA developed a new technique based on secondary electron emission (SE) and electron beam induced current (EBIC) to image the electronic structure of functioning devices with a TEM-like spatial resolution. He used this new SEEBIC technique to map the conductance of a nanodevice containing a thin silicon membrane (brown and green) separating two electrodes (blue).

Hubbard et al, "STEM Imaging with Beam-Induced Hole and Secondary Electron Currents," Physical Review Applied. 10, 044066 (2018).

Demonstration of Electron Ghost Imaging

September 11, 2018|

The first demonstration of computational ghost imaging with electrons has been carried out at UCLA. A digital micromirror device is used to directly modulate the photocathode drive laser to control the transverse distribution of a relativistic electron beam incident on a sample. Correlating the structured illumination pattern to the total sample transmission then retrieves the target image, avoiding need for a pixelated detector. In our example, we use a compressed sensing framework to improve the reconstruction quality and reduce the number of shots compared to raster scanning a small beam across the target. Compressed electron ghost imaging can reduce both acquisition time and sample damage in experiments for which spatially resolved detectors are unavailable (e.g. spectroscopy) or in which the experimental architecture precludes full frame direct imaging.

S. Li et al., "Electron Ghost Imaging," Phys. Rev. Lett. 121, 114801 (2018).

Super-Resolution Imaging of Clickable Graphene Nanoribbons Decorated with Fluorescent Dyes

July 5, 2018|

A STROBE team led by Ke Xu at Berkeley adapted advanced super-resolution microscopy techniques developed by the Weiss group at UCLA, to rapidly image graphene nanoribbons (GNRs) and carbon nanotubes (CNTs). These are important functional materials with great promise in nano-electronics and other applications. However, it has been a challenge to visualize and characterize them in a high-throughput manner due to their small physical dimensions. Temporal fluorescence intensity fluctuations in these samples enabled the reconstruction of SRM images through superresolution optical fluctuation imaging (SOFI) and the related superresolution radial fluctuation (SRRF) analysis methods.

D. Joshi et al., “Super-Resolution Imaging of Clickable Graphene Nanoribbons Decorated with Fluorescent Dyes,” Journal of the American Chemical Society 140, 9574 - 9580 (2018).

In Situ Coherent Diffractive Imaging

May 8, 2018|

The Miao group at UCLA developed a new coherent diffractive imaging technique for capturing fast nanoscale dynamics. The concept leveraged time-invariant spatial redundancy in the field of view as a powerful constraint in the phase retrieval process. In addition, the introduction of high scattering features in the spatially redundant region also suggests the potential for dose-reduced imaging. Boulder and UCLA are collaborating to apply this in-situ imaging to materials undergoing phase transitions.

Y.Hung Lo et al., “In situ coherent diffractive imaging”, Nature Communications 9, (2018).

Wave-front Shaping Controls Nonlinearity in Complex Media

May 7, 2018|

Wavefront shaping can enhance imaging through turbid media such as fog, or endoscopes. A CU Boulder STROBE team led by Rafael Piestun implemented a new kind of control that enables optimization of highly non-linear interactions through fibers. Tailoring the wave-front shape at the input, the system controls the generation of nonlinear phenomena known as stimulated-Raman-scattering cascades and four-wave-mixing, generating and shaping the different colors of the light pulses at the output of the fiber. This research has implications for the understanding of so-called adaptive systems, optical communications, fiber lasers, and imaging.

O. Tzang et al., “Adaptive wavefront shaping for controlling nonlinear multimode interactions in optical fibres” Nature Photonics 12, 368–374 (2018).

Sub-ångström Cryo-EM Structure of a Prion Protofibril Reveals a Polar Clasp

January 15, 2018|

Brain dysfunction can be caused by aggregated proteins such as prions. In humans, the prion protein causes an infection by changing its shape and transforming into rope like aggregates. In this way, stable prion aggregates are immune to normal processes of destruction in an organism and bring about neuronal death and ultimately disease. There is no molecular explanation for the variable efficiency of prion spread between species. To investigate this phenomenon, STROBE scientists Rodriguez and Maio used cryo electron microscopy to reveal the atomic structures of regions within prion that have a high propensity to form structured aggregates. This made it possible to take an atomic look at structural motifs that may represent the molecular basis for a prion species barrier.

M. Gallagher-Jones et al., “Sub-ångström cryo-EM structure of a prion protofibril reveals a polar clasp,” Nature Structural &amp Molecular Biology 25, 131 - 134 (2018).

Semiconductor Voltage Sensors for Neuron Imaging

January 12, 2018|

A STROBE team led by Simon Weiss implemented semiconductor-based voltage sensors as neuronal activity imaging probes. Unlike conventional voltage sensors, these nanosensors operating via the quantum confined Stark effect are highly sensitive, bright, and fast-responding. With further optimization, these nanosensors may enable single-particle detection and facilitate monitoring of neuronal signals at the nanoscale.

Kyoungwon Park et al., “Membrane insertion of—and membrane potential sensing by—semiconductor voltage nanosensors: Feasibility demonstration”, Science Advances 12 (2018).

Multiple Beam Illumination for Large Field-of-view, High Throughput, Imaging

January 1, 2018|

The ability to record large field of view images without a loss in spatial resolution is critical for many applications of imaging science. However, for most imaging techniques, an increase in field-of-view comes at the cost of decreased resolution. STROBE scientists at CU Boulder implemented a novel extension to ptychographic coherent diffractive imaging that permits simultaneous full-field imaging of multiple simultaneous locations on a sample, by illuminating it with spatially separated, interfering beams. This technique allows for large field-of-view imaging in amplitude and phase while maintaining diffraction-limited resolution, without an increase in collected data i.e. diffraction patterns acquired.

C. Bevis, “Multiple beam ptychography for large field of view, high throughput, quantitative phase contrast imaging,” Ultramicroscopy 184, 164–171 (2018).
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