Tartrazine clears live cells while preserving viability at high refractive indices and osmolality

bioRxiv (Cold Spring Harbor Laboratory) · 2026-04-13

Abstract Tissue-clearing techniques have transformed optical imaging of fixed specimens, yet their application to living systems remains limited by toxicity and removal of key tissue components. We recently demonstrated that absorbing molecules such as tartrazine can reversibly render live mouse skin transparent. Subsequently, it was reported that isotonic protein solutions can achieve ex vivo and in vivo cellular clearing. However, discrepancies remain regarding the optimal refractive index (RI) for live-cell clearing and the impact of elevated osmolality on cell viability. Here, using cultured mammalian cells, we systematically examine the dependence of optical contrast on medium RI and the effects of hyperosmolality. We find that, contrary to the recent report of an optimal RI of 1.36∼1.37 for suspended cells, densely-packed adherent cells exhibit a monotonic decrease in phase contrast up to an RI of 1.41 with tartrazine. Moreover, even under highly hyperosmotic conditions (∼1200 mOsm/kg), cultured cells exhibit minimal deformation and negligible loss of viability for up to 30 min in the clearing solution. These results demonstrate that tartrazine enables effective live-cell clearing at RI up to 1.41 while preserving viability under elevated osmolality, and motivate future studies to define optimal conditions for in vivo optical clearing. Graphical Abstract

Soft photonic skins with dynamic texture and colour control

Nature · 2026-01-07 · 5 citations

Direct probing of ultrafast hot-carrier injection and photo-induced degradation at Au/WS₂ interfaces using time-domain THz emission spectroscopy

2026-03-04

We investigate interfacial charge carrier dynamics and photo-induced degradation in monolayer WS₂ on gold (Au) and fused silica (SiO₂) substrates using time-domain THz emission spectroscopy, with a focus on the role of interface morphology. For excitation with photon energies above the band gap of WS₂, we observe a stronger net transient photocurrent — dominated by hole transfer from WS₂ to Au — in samples with a rugged, discontinuous van der Waals (vdW) interface. This counterintuitive result arises from asymmetric charge flow across the tunneling barrier, whereas smoother, uniform interfaces facilitate balanced electron–hole transfer, which cancels the net current. Inefficient charge separation in WS₂ on insulating SiO₂ is further linked to rapid photo-induced degradation under ambient conditions, attributed to exciton recombination at defect sites, which in turn can initiate surface chemical reactions. This study highlights the critical importance of metal–semiconductor interface morphology in governing both the dynamics of photo-generated charge carriers and sample stability of 2D material-based devices.

Interfacial control of hot-carrier extraction and photostability in two-dimensional materials

ArXiv.org · 2026-05-08

Two-dimensional transition metal dichalcogenides (TMDCs) are promising materials for next-generation optoelectronic devices, yet their implementation is hindered by limited sample stability and challenges in forming reliable electrical contacts. Here, by utilizing time-domain THz emission spectroscopy we directly probe charge carrier dynamics in monolayer WS2 on gold (Au) and fused silica (SiO2) as a function of interface morphology. For laser excitation above the band gap of WS2, we independently extract effective transport times for both electrons and holes and find that discontinuous WS2 contacts on rough Au generate larger net photocurrents than uniform, strongly coupled interfaces - a counterintuitive observation attributed to imbalanced electron and hole transfer from WS2 to Au. Crucially, we demonstrate that ultrafast charge extraction and separation suppress recombination-driven energy release and thereby prevent photo-induced degradation under ambient conditions, eliminating the need for encapsulation. These findings redefine interfacial design as a central control parameter for both performance and stability in 2D optoelectronic devices.

Hybrid-2D Excitonic Metasurfaces for Complex Amplitude Modulation

arXiv (Cornell University) · 2026-04-08

Dynamic control of visible light is crucial for technologies such as holographic displays and adaptive optics. Passive metasurfaces can shape wavefronts at the subwavelength scale and active metasurfaces promise to extend this functionality into the temporal domain. However, existing metasurfaces for dynamic phase manipulation typically cannot deliver phase modulation across a broad range without causing variations in the scattering amplitude. Here, we use an inverse-design pipeline to numerically demonstrate a hybrid-2D excitonic metasurface platform offering independent amplitude and phase control in the visible regime. Harnessing the gate-tunable excitonic response of monolayer WS2 retrieved from experiments, we design a pi-phase modulator with a uniform amplitude profile. Adding a second tunable monolayer, we achieve independent control of the amplitude and phase over the full 0-2pi phase range, which we leverage for a reconfigurable beam-steering metadevice. Our results demonstrate how hybrid-2D excitonic metasurfaces enable electrically tunable wavefront shaping in the visible regime.

Interfacial control of hot-carrier extraction and photostability in two-dimensional materials

arXiv (Cornell University) · 2026-05-08

Two-dimensional transition metal dichalcogenides (TMDCs) are promising materials for next-generation optoelectronic devices, yet their implementation is hindered by limited sample stability and challenges in forming reliable electrical contacts. Here, by utilizing time-domain THz emission spectroscopy we directly probe charge carrier dynamics in monolayer WS2 on gold (Au) and fused silica (SiO2) as a function of interface morphology. For laser excitation above the band gap of WS2, we independently extract effective transport times for both electrons and holes and find that discontinuous WS2 contacts on rough Au generate larger net photocurrents than uniform, strongly coupled interfaces - a counterintuitive observation attributed to imbalanced electron and hole transfer from WS2 to Au. Crucially, we demonstrate that ultrafast charge extraction and separation suppress recombination-driven energy release and thereby prevent photo-induced degradation under ambient conditions, eliminating the need for encapsulation. These findings redefine interfacial design as a central control parameter for both performance and stability in 2D optoelectronic devices.

Metasurface-enhanced Momentum-resolved Circular Dichroism Spectroscopy

ChemRxiv · 2026-03-29

Nanophotonic resonators can amplify weak molecular circular dichroism (CD) signals, but the structural chirality from angle-dependent photoexcitation or collection may mask intrinsic, molecular chiroptical features. Here, we develop an achiral nanodisk array and angle-resolved spectral measurement approach which deconvolves chiral molecular and substrate signals and enables artifact-free chiral-optical enhancement. Circular polarization-resolved momentum-space spectroscopy maps chiroptical response across wavelength and collection angle in a single measurement, simultaneously reporting intrinsic, molecularly-linked CD and extrinsic, nanostructure-induced signals in distinct optical channels. As a model system, we design silicon nitride nanodisks that overlap spectrally with thiocamphor’s CD features with a simulated ~150 fold, uniform-sign enhancement in the volume-averaged density of optical chirality within the analyte-accessible region. We validate the enhancement of otherwise weak CD signals with the predicted spectral and angular sensitivity in a thiocamphor solution and measure its enantiomeric excesses. Thiocamphor concentrations down to 0.1 mM are detected with robust quantification established at 1 mM, supporting at least one order of magnitude limit of detection improvement relative to a conventional measurement at comparable path length. Additionally, this enhanced CD response demonstrates a monotonically increasing dose–response behavior across enantiomeric excesses ranging from 1% to 25%, consistent with a linear trend across the measured range. Our approach demonstrates momentum-resolved, metasurface-enhanced CD spectroscopy as a promising path to reliable and sensitive detection of molecular chirality and enantiomeric purity.

Hybrid-2D Excitonic Metasurfaces for Complex Amplitude Modulation

Nano Letters · 2026-04-30

retrieved from experiments, we design a π-phase modulator with a uniform amplitude profile. Adding a second tunable monolayer, we achieve independent control of the amplitude and phase over the full 0-2π phase range, which we leverage for a reconfigurable beam-steering metadevice. Our results demonstrate how hybrid-2D excitonic metasurfaces enable electrically tunable wavefront shaping in the visible regime.

Hybrid-2D Excitonic Metasurfaces for Complex Amplitude Modulation

arXiv (Cornell University) · 2026-04-08

Dynamic control of visible light is crucial for technologies such as holographic displays and adaptive optics. Passive metasurfaces can shape wavefronts at the subwavelength scale and active metasurfaces promise to extend this functionality into the temporal domain. However, existing metasurfaces for dynamic phase manipulation typically cannot deliver phase modulation across a broad range without causing variations in the scattering amplitude. Here, we use an inverse-design pipeline to numerically demonstrate a hybrid-2D excitonic metasurface platform offering independent amplitude and phase control in the visible regime. Harnessing the gate-tunable excitonic response of monolayer WS2 retrieved from experiments, we design a pi-phase modulator with a uniform amplitude profile. Adding a second tunable monolayer, we achieve independent control of the amplitude and phase over the full 0-2pi phase range, which we leverage for a reconfigurable beam-steering metadevice. Our results demonstrate how hybrid-2D excitonic metasurfaces enable electrically tunable wavefront shaping in the visible regime.

Dynamic Excitonic Beam Switching with Atomically‐Thin Binary Blazed Gratings

Advanced Optical Materials · 2025-05-01 · 2 citations

Abstract Beam steering metasurfaces are ultra‐compact optical coatings that offer on‐demand redirection of optical power to specific diffraction orders. To achieve this, spatial gradients are commonly introduced in the phase of light scattered by plasmon or Mie resonant nanoparticles within the metasurface grating's unit cell. However, these phase gradients are oftentimes difficult to tune post‐fabrication. Recently, excitons in monolayer 2D semiconductors have emerged as a new metasurface building block, due to their strong and electrically‐tunable resonant light‐matter interaction. These 2D excitonic metasurfaces offer the tantalizing prospect of beam switching within a single monolayer. Here, it is demonstrated how the 2D analog of binary blazed gratings enables such beam switching by mere nanopatterning of a large monolayer WS 2 , even though nanoscale ribbons of WS 2 do not support geometrical resonances. By introducing a gradient in the nanoribbon width within the metasurface unit cell, an amplitude gradient combined with a small phase gradient in the scattered fields results in asymmetric diffraction efficiencies. Using a scattered‐field analysis, it is shown that these gradients can be further engineered via interference effects with the substrate reflection. Finally, the electrical tunability of the exciton resonance is leveraged to achieve selective and dynamic beam switching with an atomically‐thin metasurface.