Procedures for cryogenic X-ray ptychographic imaging of biological samples

X-ray Ptychography Imaging of Human Chromosomes After Low-dose Irradiation

Studies of the structural and functional role of chromosomes in cytogenetics have spanned more than 10 decades. In this work, we take advantage of the coherent X-rays available at the latest synchrotron sources to extract the individual masses of all 46 chromosomes of metaphase human B and T cells using hard X-ray ptychography. We have produced ‘X-ray karyotypes’ of both heavy metal–stained and unstained spreads to determine the gain or loss of genetic material upon low-level X-ray irradiation doses due to radiation damage. The experiments were performed at the I-13 beamline, Diamond Light Source, Didcot, UK, using the phase-sensitive X-ray ptychography method.

Cryo-nanoscale chromosome imaging-future prospects

The high-order structure of mitotic chromosomes remains to be fully elucidated. How nucleosomes compact at various structural levels into a condensed mitotic chromosome is unclear. Cryogenic preservation and imaging have been applied for over three decades, keeping biological structures close to the native in vivo state. Despite being extensively utilized, this field is still wide open for mitotic chromosome research. In this review, we focus specifically on cryogenic efforts for determining the mitotic nanoscale chromatin structures. We describe vitrification methods, current status, and applications of advanced cryo-microscopy including future tools required for resolving the native architecture of these fascinating structures that hold the instructions to life.

Cells Undergo Major Changes in the Quantity of Cytoplasmic Organelles after Uptake of Gold Nanoparticles with Biologically Relevant Surface Coatings

Here, we use cryo soft X-ray tomography (cryo-SXT), which delivers 3D ultrastructural volumes of intact cells without chemical fixation or staining, to gain insight about nanoparticle uptake for nanomedicine. We initially used dendritic polyglycerol sulfate (dPGS) with potential diagnostic and therapeutic applications in inflammation. Although dPGS-coated gold nanoparticle (dPGS-AuNP) uptake followed a conventional endocytic/degradative pathway in human lung epithelial cell lines (A549), with cryo-SXT, we detected ∼5% of dPGS-AuNPs in the cytoplasm, a level undetectable by confocal light microscopy. We also observed ∼5% of dPGS-AuNPs in a rarely identified subcellular site, namely, lipid droplets, which are important for cellular energy metabolism. Finally, we also found substantial changes in the quantity of cytoplasmic organelles upon dPGS-AuNP uptake over the 1-6 h incubation period; the number of small vesicles and mitochondria significantly increased, and the number of multivesicular bodies and the number and volume of lipid droplets significantly decreased. Although nearly all organelle numbers at 6 h were still significantly different from controls, most appeared to be returning to normal levels. To test for generality, we also examined cells after uptake of gold nanoparticles coated with a different agent, polyethylenimine (PEI), used for nucleic acid delivery. PEI nanoparticles did not enter lipid droplets, but they induced similar, albeit less pronounced, changes in the quantity of cytoplasmic organelles. We confirmed these changes in organelle quantities for both nanoparticle coatings by confocal fluorescence microscopy. We suggest this cytoplasmic remodeling could reflect a more common cellular response to coated gold nanoparticle uptake.

Super-resolution near-field ptychography

Compared to far-field ptychography, near-field ptychography can reduce the requirement on the detector dynamic range, while it is able to cover a larger field of view with a fewer number of sample scans. However, its spatial resolution is limited by the detector pixel size. Here, we utilize a pixel-super-resolved approach to overcome this limitation. The method has been applied to four types of experiment configurations using planar and divergent illuminations together with two different cameras with highly contrast specifications. The proposed method works effectively for up-sampling up to 6 times. Meanwhile, it can achieve ∼5.9-fold and ∼3.1-fold resolution improvement over the 6.5-μm and 2.4-μm detector pixel size. We also demonstrate the precisely quantitative phase imaging capability of the method by using a phase resolution target. The presented method is believed to have great potential in X-ray tomography and on-chip flow cytometry.

Use of 3D imaging for providing insights into high-order structure of mitotic chromosomes

The high-order structure of metaphase chromosomes remains still under investigation, especially the 30-nm structure that is still controversial. Advanced 3D imaging has provided useful information for our understanding of this detailed structure. It is evident that new technologies together with improved sample preparations and image analyses should be adequately combined. This mini review highlights 3D imaging used for chromosome analysis so far with future imaging directions also highlighted.

X-ray diffraction imaging of cardiac cells and tissue

With the development of advanced focusing optics for x-rays, we can now use x-ray beams with spot sizes in the micro- or nanometer range to scan cells and large areas of tissues and continuously record the diffraction signals. From this data, x-ray scattering maps or so-called x-ray darkfield images are computed showing how different types of cells or regions of tissues differ in their diffraction intensity. At the same time a diffraction pattern is available for each scan point which encodes the local nanostructure, averaged over many contributing constituents illuminated by the beam. In this work we have exploited these new capabilities of scanning x-ray diffraction to investigate cardiac muscle cells as well as cardiac tissue. We give examples of how cardiac cells, especially living, cultured cells, can be prepared to be compatible with the instrumentation constraints of nano- or micro-diffraction instruments. Furthermore, we show how the developmental stage, ranging from neonatal to adult cells, as well as the final preparation state of the cardiomyocytes influences the recorded scattering signal and how these diffraction signals compare to the structure of a fully developed cardiac muscle.