Single-beam multimodal nonlinear-optical imaging of structurally complex events in cell-cycle dynamics

Multimodal label-free imaging of murine hepatocellular carcinoma with a subcellular resolution

We demonstrate label-free imaging of genetically induced hepatocellular carcinoma (HCC) in a murine model provided by two- and three-photon fluorescence microscopy of endogenous fluorophores excited at the central wavelengths of 790, 980 and 1250 nm and reinforced by second and third harmonic generation microscopy. We show, that autofluorescence imaging presents abundant information about cell arrangement and lipid accumulation in hepatocytes and hepatic stellate cells (HSCs), harmonics generation microscopy provides a versatile tool for fibrogenesis and steatosis study. Multimodal images may be performed by a single ultrafast laser source at 1250 nm falling in tissue transparency window. Various grades of HCC are examined revealing fibrosis, steatosis, liver cell dysplasia, activation of HSCs and hepatocyte necrosis, that shows a great ability of multimodal label-free microscopy to intravital visualization of liver pathology development.

Thermal and Quantum Barrier Passage as Potential-Driven Markovian Dynamics

Rapidly progressing laser technologies provide powerful tools to study potential barrier-passage dynamics in physical, chemical, and biological systems with unprecedented temporal and spatial resolution and a remarkable chemical and structural specificity. The available theories of barrier passage, however, operate with equations, potentials, and parameters that are best suited for a specific area of research and a specific class of systems and processes. Making connections among these theories is often anything but easy. Here, we address this problem by presenting a unified framework for the description of a vast variety of classical and quantum barrier-passage phenomena, revealing an innate connection between various types of barrier-passage dynamics and providing closed-form equations showing how the signature exponentials in classical and quantum barrier-passage rates relate to and translate into each other. In this framework, the Arrhenius-law kinetics, the emergence of the Gibbs distribution, Hund's molecular wave-packet well-to-well oscillatory dynamics, Keldysh photoionization, and Kramers' escape over a potential barrier are all understood as manifestations of a potential-driven Markovian dynamics whereby a system evolves from a state of local stability. Key to the irreducibility of quantum tunneling to thermally activated barrier passage is the difference in the ways the diffusion-driving potentials emerge in these two tunneling settings, giving rise to stationary states with a distinctly different structure.

First passage time of laser-driven tunneling

The notion of the first passage time is shown to offer a meaningful extension to quantum tunneling, providing a closed-integral-form analytical unification of the tunneling rate and the tunneling passage time. We demonstrate that, in suitable potential settings, the quantum first passage time, found as a solution to the Fokker-Planck and backward Kolmogorov's equations for the quantum probability density, recovers the hallmark results for the Kramers escape rate, the lifetime of tunneling quasi-stationary wave packets, leads to a classical, distance-over-speed passage time for a free-particle wave function, and offers useful insights into Keldysh's intimation on the electron barrier-traversal time in field-induced ionization.

Real-time fiber-optic recording of acute-ischemic-stroke signatures

We present an experimental framework and methodology for in vivo studies on rat stroke models that enable a real-time fiber-optic recording of stroke-induced hydrogen peroxide and pH transients in ischemia-affected brain areas. Arrays of reconnectable implantable fiber probes combined with advanced optogenetic fluorescent protein sensors are shown to enable a quantitative multisite time-resolved study of oxidative-stress and acidosis buildup dynamics as the key markers, correlates and possible drivers of ischemic stroke. The fiber probes designed for this work provide a wavelength-multiplex forward-propagation channel for a spatially localized, dual-pathway excitation of genetically encoded fluorescence-protein sensors along with a back-propagation channel for the fluorescence return from optically driven fluorescence sensors. We show that the spectral analysis of the fiber-probe-collected fluorescence return provides means for a high-fidelity autofluorescence background subtraction, thus enhancing the sensitivity of real-time detection of stroke-induced transients and significantly reducing measurement uncertainties in in vivo acute-stroke studies as inherently statistical experiments operating with outcomes of multiply repeated measurements on large populations of individually variable animal stroke models.

Imaging approaches for monitoring three-dimensional cell and tissue culture systems

The past decade has seen an increasing demand for more complex, reproducible and physiologically relevant tissue cultures that can mimic the structural and biological features of living tissues. Monitoring the viability, development and responses of such tissues in real-time are challenging due to the complexities of cell culture physical characteristics and the environments in which these cultures need to be maintained in. Significant developments in optics, such as optical manipulation, improved detection and data analysis, have made optical imaging a preferred choice for many three-dimensional (3D) cell culture monitoring applications. The aim of this review is to discuss the challenges associated with imaging and monitoring 3D tissues and cell culture, and highlight topical label-free imaging tools that enable bioengineers and biophysicists to non-invasively characterise engineered living tissues.

Imaging through a scattering medium: the Fisher information and the generalized Abbe limit

Enhanced-resolution imaging in complex scattering media is revisited from a parameter estimation perspective. A suitably defined Fisher information is shown to offer useful insights into the limiting precision of parameter estimation in a scattering environment and, hence, into the limiting spatial resolution that can be achieved in imaging-through-scattering settings. The Fisher information that defines this resolution limit via the Cramér-Rao lower bound is shown to scale with the number of adaptively controlled space-time modes of the probe field, suggesting a physically intuitive generalization of the Abbe limit to the spatial resolution attainable for complex scattering systems. In a conventional, direct-imaging microscopy setting, this bound is shown to converge to the canonical Abbe limit.