Glacial lake outburst floods threaten China-Nepal connectivity: Synergistic study of remote sensing, GIS and hydrodynamic modeling with regional implications.

Holistic study of glacial lakes and glacial lake outburst floods (GLOFs) in the strategically important China-Nepal transportation corridors is imperative for regional connectivity and disaster risk reduction. This study focuses on four China-Nepal transportation corridors, namely Chentang-Kimathanka, Zhangmu-Kodari, Keyrung-Kathmandu and Taklakot-Hilsa from east to west in the Himalayan region. Within a remote integrated framework, we present the latest high-resolution inventory of glacial lakes, assess their decadal spatio-temporal changes (1992-2022), identify potentially dangerous glacial lakes, and apply hydrodynamic model to assess downstream impacts of possible GLOFs along the study area.

Surpassing the resolution limitation of structured illumination microscopy by an untrained neural network.

Structured illumination microscopy (SIM), as a flexible tool, has been widely applied to observing subcellular dynamics in live cells. It is noted, however, that SIM still encounters a problem with theoretical resolution limitation being only twice over wide-field microscopy, where imaging of finer biological structures and dynamics are significantly constrained. To surpass the resolution limitation of SIM, we developed an image postprocessing method to further improve the lateral resolution of SIM by an untrained neural network, i.

A Phase-Shifted Surface Plasmon Resonance Sensor for Simultaneous Photoacoustic Volumetric Imaging and Spectroscopic Analysis.

For biomedical photoacoustic applications, an ongoing challenge in simultaneous volumetric imaging and spectroscopic analysis arises from ultrasonic detectors lacking high sensitivity to pressure transients over a broad spectral bandwidth. Photoacoustic impulses can be measured on the basis of the ultrafast temporal dynamics and highly sensitive response of surface plasmon polaritons to the refractive index changes. Taking advantage of the ultra-sensitive phase shift of surface plasmons caused by ultrasonic perturbations instead of the reflectivity change [as is the case for traditional surface plasmon resonance (SPR) sensors], a novel SPR sensor based on phase-shifted interrogation was developed for the broadband measurement of photoacoustically induced pressure transients with improved detection sensitivity.

Ultrasonic signal detection based on Fabry-Perot cavity sensor.

Acoustic/ultrasonic sensors are devices that can convert mechanical energy into electrical signals. The Fabry-Perot cavity is processed on the end face of the double-clad fiber by a two-photon three-dimensional lithography machine. In this study, the outer diameter of the core cladding was 250 μm, the diameter of the core was 9 μm, and the microcavity sensing unit was only 30 μm.

High-performance imaging of cell-substrate contacts using refractive index quantification microscopy.

Non-invasive imaging of living cells is an advanced technique that is widely used in the life sciences and medical research. We demonstrate a refractive index quantification microscopy (RIQM) that enables label-free studies of glioma cell-substrate contacts involving cell adhesion molecules and the extracellular matrix. This microscopy takes advantage of the smallest available spot created when an azimuthally polarized perfect optical vortex beam (POV) is tightly focused with a first-order spiral phase, which results in a relatively high imaging resolution among biosensors.

Graphene-Based Confocal Refractive Index Microscopy for Label-Free Differentiation of Living Epithelial and Mesenchymal Cells.

Label-free imaging and investigation of living cells are significant for many biomedical studies. It has been challenging to detect the epithelial-mesenchymal transition of cells in situ without affecting cellular activity. Here, we present a common-path differential confocal microscope based on the polarization-sensitive absorption of graphene to realize high-performance refractive index imaging and differentiation of living colorectal cancer cells (HCT116) with large detecting depth (1.

Refractive index sensing and imaging based on polarization-sensitive graphene.

Graphene exhibits extraordinary opto-electronic properties due to its unique dynamic conductivity, bringing great value in optical sensing, surface plasmon modulation and photonic devices. Based on the polarization-sensitive absorption of graphene working at near infrared to ultraviolet wavelengths, we theoretically investigate the refractive index sensing and imaging mechanism under oblique and tight focusing incidences of light respectively. We demonstrate that such graphene-based methods can provide ultrahigh refractive index resolution (∼2.

In Vivo Reflection-Mode Photoacoustic Microscopy Enhanced by Plasmonic Sensing with an Acoustic Cavity.

Relying on high-sensitivity refractive index sensing and a highly constrained evanescent field of surface plasmon resonance (SPR), broadband photoacoustic (PA) pressure transients were measured using an SPR sensor instead of routinely used piezoelectric ultrasonic transducers. An acoustic cavity made from stainless steel and having a designed ellipsoidal inner surface redirected laser-induced PA waves from the PA excitation spot to the SPR sensor. By incorporating the SPR sensor with the acoustic cavity, we developed optical-resolution photoacoustic microscopy (OR-PAM) with multiple advantages, including reflection-mode signal capture, improved PA detection sensitivity, increased PA spectral bandwidth as broad as ∼98 MHz, and micrometer-scale lateral resolution.

Isometrically Resolved Photoacoustic Microscopy Based on Broadband Surface Plasmon Resonance Ultrasound Sensing.

Photoacoustic microscopy (PAM) can measure optical absorption-based molecular specificities within tissues. Despite the diffraction-limited lateral resolution in optical-resolution photoacoustic microscopy (OR-PAM), the ongoing challenge is poor axial resolution because of an insufficient ultrasound detection bandwidth, which hampers PAM volumetric imaging. We propose polarization-differential surface plasmon resonance (SPR) sensing for broadband and high-sensitivity photoacoustic (PA) detection, allowing OR-PAM with comparable resolution along lateral and axial directions.

Low-loss metal-dielectric waveguide mode enabled structured illumination microscopy with 0.18λ resolution.

Structured illumination microscopy (SIM) is a powerful super-resolved imaging technique which enables to perform fast and in vivo imaging of bio-samples. In order to achieve a better resolution of a SIM system, evanescent waves with larger in-plane wave-vector are preferred for SIM, among which the total internal reflection (TIRF-SIM) and the plasmonic SIM (pSIM) configurations are widely studied. Here, we demonstrated a metal-dielectric waveguide (MDW) based SIM system - termed as MDW-SIM, which can achieve a good compromise between TIRF-SIM and pSIM.

Broadband graphene-based photoacoustic microscopy with high sensitivity.

Photoacoustic microscopy (PAM) enables the measurement of properties associated with optical absorption within tissues and complements sophisticated technologies employing optical microscopy. An inadequate frequency response as determined by a piezoelectric ultrasonic transducer results, however, in poor depth resolution and inaccurate measurements of the coefficients of optical absorption. We developed a PAM system configured as an attenuated total reflectance sensor with a ten-layer graphene film sandwiched between a prism and water (the coupling medium) for photoacoustic (PA) wave detection.

Real-time subcellular imaging based on graphene biosensors.

Non-invasive living cell microscopy in real time is essential for a wide variety of biomedical research. Here, we present a subcellular refractive index imaging technique for living cells based on a graphene biosensor system. Owing to the optical reflectivity differences of graphene to s- and p-polarizations, a 45° generalized-cylindrical-vector-polarized laser beam is employed to demodulate the reflected cylindrical vector beam for differential detecting.

Sub-100nm resolution PSIM by utilizing modified optical vortices with fractional topological charges for precise phase shifting.

We demonstrate an all-optical plasmonic structured illumination microscopy (PSIM) technique. A set of plasmonic standing-wave patterns is excited by amplitude-modified optical vortices (OVs), which have fractional topological charges for precise phase shift of {-2π/3, 0, 2π/3}. A specially designed optical aperture is introduced to modify the OVs in order to improve the uniformity of interference patterns.

Phase-stepping technique for highly sensitive microscopic surface plasmon resonance biosensor.

In this paper, the phase-stepping technique is applied to improve a phase-sensitive surface plasmon resonance biosensor based on differential interferometry between focused radially polarized and azimuthally polarized cylindrical vector beams. Detailed analysis is presented for the phase-stepping method, and the least squares unwrapping algorithm is employed to detect the phase distribution in correspondence to the refractive index of sample. Benefiting from the phase-stepping technique, both the measurement speed and sensitivity are improved significantly.

Plasmonic petal-shaped beam for microscopic phase-sensitive SPR biosensor with ultrahigh sensitivity.

Differential phase measurement between radially polarized (RP) and azimuthally polarized (AP) beams is an important technique in microscopic surface plasmon resonance (SPR) biosensors as reported in our earlier works [Opt. Lett.37, 2091 (2012); Appl.

Focused cylindrical vector beam assisted microscopic pSPR biosensor with an ultra wide dynamic range.

A novel phase-sensitive surface plasmon resonance (pSPR) biosensor based on differential phase measurement between two cylindrical vector beams, namely radially polarized and azmuthally polarized beams, is proposed and studied in an inverted microscope. Different from a fixed angle or a relatively small angular range for SPR excitation in the attenuated total reflection (ATR) configuration, the signal beam focused by a total internal reflection fluorescence microscopic objective contains the entire angular range from 0 to the maximum angle given by the numerical aperture, leading to a dynamic range of 0.41 RIU which is over seven times wider than the best result of the ATR pSPR sensor.