Cell death detection by quantitative three-dimensional single-cell tomography

Integration of cellular-resolution optical coherence tomography and Raman spectroscopy for discrimination of skin cancer cells with machine learning

Significance

An integrated cellular-resolution optical coherence tomography (OCT) module with near-infrared Raman spectroscopy was developed on the discrimination of various skin cancer cells and normal cells. Micron-level three-dimensional (3D) spatial resolution and the spectroscopic capability on chemical component determination can be obtained simultaneously.

Aim

We experimentally verified the effectiveness of morphology, intensity, and spectroscopy features for discriminating skin cells.

Approach

Both spatial and spectroscopic features were employed for the discrimination of five types of skin cells, including keratinocytes (HaCaT), the cell line of squamous cell carcinoma (A431), the cell line of basal cell carcinoma (BCC-1/KMC), primary melanocytes, and the cell line of melanoma (A375). The cell volume, compactness, surface roughness, average intensity, and internal intensity standard deviation were extracted from the 3D OCT images. After removing the fluorescence components from the acquired Raman spectra, the entire spectra (600 to 2100    cm - 1 ) were used.

Results

An accuracy of 85% in classifying five types of skin cells was achieved. The cellular-resolution OCT images effectively differentiate cancer and normal cells, whereas Raman spectroscopy can distinguish the cancer cells with nearly 100% accuracy.

Conclusions

Among the OCT image features, cell surface roughness, internal average intensity, and standard deviation of internal intensity distribution effectively differentiate the cancerous and normal cells. The three features also worked well in sorting the keratinocyte and melanocyte. Using the full Raman spectra, the melanoma and keratinocyte-based cell carcinoma cancer cells can be discriminated effectively.

Optical coherence tomography modeling incorporating scattering, absorption, and multiple reflections

A direct scattering optical coherence tomography forward model was developed to simulate A-scans for both idealized and real light sources on an arbitrary given sample structure. Previous models neglected absorption, scattering, and multiple reflections at interfacial layers, and so two extended models were developed to investigate the impact of these processes. The first model uses the Beer-Lambert law to incorporate both absorption and scattering optical processes, and the second model uses a recursive form to model multiple reflections. These models were tested on a structure representative of a multilayered skin sample. The results show that the absorption and scattering processes have significant impact on the height of the peaks in the simulated A-scans. Conversely, the incorporation of multiple reflections has very little impact on the height of these peaks. Neither of the above processes has any impact on the locations of the A-scan peaks, which are associated with the sample interfaces between layers.

Segmentation of nucleus and cytoplasm of a single cell in three-dimensional tomogram using optical coherence tomography

A random rayburst sampling (RRBS) framework was developed to detect the nucleus and cell membrane boundaries in three-dimensional (3-D) space. Raw images were acquired through a full-field optical coherence tomography system with submicron resolution—i.e., 0.8 ?? ? m in lateral and 0.9 ?? ? m in axial directions. The near-isometric resolution enables 3-D segmentation of a nucleus and cell membrane for determining the volumetric nuclear-to-cytoplasmic (N/C) ratio of a single cell. The RRBS framework was insensitive to the selection of seeds and image pixel noise. The robustness of the RRBS framework was verified through the convergence of the N/C ratio searching algorithm. The relative standard deviation of the N/C ratio between different randomly selected seed sets was only 2%. This technique is useful for various in vitro assays on single-cell analyses.

Ligand-Driven and Full-Color-Tunable Fiber Source: Toward Next-Generation Clinic Fiber-Endoscope Tomography with Cellular Resolution

In many biomedical applications, broad full-color emission is important, especially for wavelengths below 450 nm, which are difficult to cover via supercontinuum generation. Single-crystalline-core sapphires with defect-driven emissions have potential roles in the development of next-generation broadband light sources because their defect centers demonstrate multiple emission bands with tailored ligand fields. However, the inability to realize high quantum yields with high crystallinity by conventional methods hinders the applicability of ultra-broadband emissions. Here, we present how an effective one-step fiber-drawing process, followed by a simple and controllable thermal treatment, enables a low-loss, full-color, and crystal fiber-based generation with substantial color variability. The broad spectrum extends from 330 nm, which is over 50 nm further into the UV region than that in previously reported results. The predicted submicrometer spatial resolutions demonstrate that the defect-ligand fields are potentially beneficial for achieving in vivo cellular tomography. It is also noteworthy that the efficiency of the milliwatt-level full-color generation, with an optical-to-optical efficiency of nearly 5%, is the highest among that of the existing active waveguide schemes. In addition, direct evidence from high-resolution transmission electron microscopy together with electron energy loss spectroscopy and crystal-field ligands reveals an excellent crystalline core, atomically defined core/cladding interfacial roughness, and significant enhancements in new laser-induced electronic defect levels. Our work suggests an inexpensive, facile, and highly scalable route toward achieving cellular-resolution tomographic imaging and represents an important step in the development of endoscope-compatible diagnostic devices.

Assesment of apoptosis induced changes in scattering using optical coherence tomography

The aim of this study is to identify changes in scattering with optical coherence tomography (OCT) and relate these measurements with mitochondrial changes during the initiation of apoptosis. Human retinal pigment epithelial cells were cultured and apoptosis was induced using 10% alcohol. Using the attenuation coefficient and backscattering, changes were measured during cell death in a cell-pellet and monolayer respectively. To confirm apoptosis, fluorescent activated cell sorting was used. Mitochondrial activity during apoptosis was assessed using an oxidative stress assay and fluorescent confocal microscopy. Pelleted apoptotic cells measured with OCT showed a clear rise while untreated cells showed a very small increase in attenuation coefficient. Monolayered apoptotic cells displayed a distinct increase, while untreated cells showed a small increase in the backscattering. Apoptosis was confirmed by FACS experiments. Mitochondrial changes during the onset of apoptosis were also measured. The results demonstrate that apoptotic cell death could be monitored in real-time by OCT. Changes in the scattering after induction of apoptosis are likely to be related to changes in the intracellular morphology. Oxidative stress-induced mitochondrial swelling could be responsible for the initial increase, while cell blebbing and secondary necrosis subsequently for the observed decrease in scattering.

Broadband Ce/Cr-doped crystal fibers for high axial resolution OCT light source

The fabrication and characteristics of Ce/Cr-doped crystal fibers employing drawing tower technique are reported. The fluorescence spectrum of the Ce/Cr fibers at the core diameter ranging from 10 to 21 µm exhibited a 200-nm near-Gaussian broadband emission which enabled to provide an axial resolution of 1.8-μm and a power density of 79.1 nW/nm. The proposed broadband Ce/Cr-doped crystal fibers may be provided as a high-resolution light source for the use in optical coherence tomography system as well as industrial inspection and biomedical imaging applications.

The substrate matters in the Raman spectroscopy analysis of cells

Raman spectroscopy is a powerful analytical method that allows deposited and/or immobilized cells to be evaluated without complex sample preparation or labeling. However, a main limitation of Raman spectroscopy in cell analysis is the extremely weak Raman intensity that results in low signal to noise ratios. Therefore, it is important to seize any opportunity that increases the intensity of the Raman signal and to understand whether and how the signal enhancement changes with respect to the substrate used. Our experimental results show clear differences in the spectroscopic response from cells on different surfaces. This result is partly due to the difference in spatial distribution of electric field at the substrate/cell interface as shown by numerical simulations. We found that the substrate also changes the spatial location of maximum field enhancement around the cells. Moreover, beyond conventional flat surfaces, we introduce an efficient nanostructured silver substrate that largely enhances the Raman signal intensity from a single yeast cell. This work contributes to the field of vibrational spectroscopy analysis by providing a fresh look at the significance of the substrate for Raman investigations in cell research.

Longitudinal label-free tracking of cell death dynamics in living engineered human skin tissue with a multimodal microscope

We demonstrate real-time, longitudinal, label-free tracking of apoptotic and necrotic cells in living tissue using a multimodal microscope. The integrated imaging platform combines multi-photon microscopy (MPM, based on two-photon excitation fluorescence), optical coherence microscopy (OCM), and fluorescence lifetime imaging microscopy (FLIM). Three-dimensional (3-D) co-registered images are captured that carry comprehensive information of the sample, including structural, molecular, and metabolic properties, based on light scattering, autofluorescence intensity, and autofluorescence lifetime, respectively. Different cell death processes, namely, apoptosis and necrosis, of keratinocytes from different epidermal layers are longitudinally monitored and investigated. Differentiation of the two cell death processes in a complex living tissue environment is enabled by quantitative image analysis and high-confidence classification processing based on the multidimensional, cross-validating imaging data. These results suggest that despite the limitations of each individual label-free modality, this multimodal imaging approach holds the promise for studies of different cell death processes in living tissue and in vivo organs.

Simple and efficient defect-tailored fiber-based UV-VIS broadband white light generation

We propose and demonstrate a facile approach for ultraviolet-visible broadband generation from a sapphire crystal core-borosilicate glass cladding hybrid fiber using a laser-heated pedestal growth technique. Considerable formation of F- and F(2)-type color emitters is effectively facilitated by Ti(4+) ions and Al(3+) vacancies, retaining efficient luminescence and high crystallinity of the sapphire core. These color centers intensify the ultraviolet, blue, and green emissions at 370, 450, and 540 nm, whereas the 650-nm red emission is contributed by Cr(3+) in the octahedral sites of the corundum structure. Over 1-mW white light with an optical-to-optical efficiency of up to nearly 5% and 1931 Commission International de l'Eclairage chromaticity coordinate of (0.287, 0.333) is achieved under 325-nm excitation.