In a groundbreaking advancement poised to revolutionize photodynamic therapy, researchers at Tsinghua University, China, have unveiled a novel approach to rapidly produce singlet oxygen with unprecedented efficiency and precision. This achievement stems from integrating the principles of bound states in the continuum (BIC) into meticulously engineered metasurfaces, marking a significant leap beyond the limitations that have hampered traditional molecular photosensitizers for decades.

Singlet oxygen, the excited state of molecular oxygen with formidable cytotoxic capabilities, has long been a cornerstone in targeting tumor cells via photodynamic therapy. Conventional production methods rely heavily on molecular photosensitizers, which suffer from inherent drawbacks such as photobleaching, limited wavelength selectivity, and biocompatibility issues. Metallic and semiconductor nanostructures emerged as alternatives due to their photostability; however, their quantum yields for singlet-oxygen generation remained too low to enable rapid, localized therapeutic outcomes under clinically viable low-dose illumination.

The breakthrough by Prof. Xing Fu and Prof. Qiang Liu’s team transcends these constraints by leveraging quasi-bound states in the continuum within an innovative Au–TiO₂ metasurface design. This architecture comprises elliptical TiO₂ nanopillars capped with an ultrathin 7 nm gold layer, engineered with subtle symmetry breaking that transforms a theoretically non-radiative BIC into a radiative quasi-BIC resonance. This purposeful symmetry perturbation dramatically enhances visible-light absorption at 532 nm, achieving an impressive 45% absorption within an optical path mere hundreds of nanometers thick. Such efficiency in light capture is vital to triggering the subsequent photochemical processes.

Under continuous-wave laser excitation, the metasurface’s enhanced near-field intensities lead to a marked elevation of the electronic temperature in the gold layer. This phenomenon facilitates the generation of energetic “hot carriers,” electrons that possess sufficient energy to inject into the conduction band of TiO₂. These injected electrons then catalyze interfacial redox reactions with the surrounding oxygen molecules, converting the triplet ground state into the highly reactive singlet oxygen species. The geometric design ensures that this reaction zone is tightly confined adjacent to the metasurface, enabling a concentrated and narrowly localized reactive oxygen environment.

Critically, the researchers have circumvented a prevailing issue in photocatalysis: the trade-off between metal loading and carrier lifetime. Typically, increasing metallic content amplifies light absorption but simultaneously accelerates carrier recombination, thus hindering catalytic efficiency. By maintaining an ultra-thin gold layer and leveraging the quasi-BIC resonance, the team achieved robust absorption with minimal metal volume, preserving extended carrier lifetimes and promoting efficient charge transfer.

One of the most remarkable outcomes of this advancement is the striking enhancement in singlet-oxygen quantum yield—surpassing conventional methods by an astonishing six orders of magnitude. This rapid, molar-level production occurs within mere seconds of illumination at continuous-wave operation, signifying a quantum leap in both speed and scale of reactive oxygen species generation suitable for therapeutic and chemical applications.

Beyond sheer efficiency, the metasurface’s resonant properties offer programmable selectivity. By geometrically scaling the nanopillar array, the resonance wavelength can be precisely tuned, enabling selective activation at desired illumination wavelengths. This spectral addressability facilitates spatially resolved cytotoxic effects, with demonstrated pixel-wise control over tumor-cell apoptosis guided by patterned illumination. Notably, this approach obviates the need for molecular photosensitizers, thereby sidestepping associated stability and compatibility issues.

The interplay of plasmonic and dielectric components within the metasurface underpins these photochemical innovations. While gold nanoparticles have historically served as hot-carrier generators in photocatalytic systems, coupling with TiO₂ elliptical nanopillars tuned near their BIC transitions magnifies the near-field enhancement and modulates charge dynamics. This synergy represents a paradigm shift in designing photocatalytic interfaces tailored for high-efficiency photon-to-chemical conversions.

Moreover, the localized generation of singlet oxygen holds significant promise for clinical applications beyond photodynamic cancer therapy. The capacity for rapid, spatially precise reactive species generation could impact selective oxidation reactions in chemical synthesis, environmental remediation, and microfluidic reactor technologies. The ability to deploy low doses of light while achieving targeted chemical effects is a profound advantage in reducing collateral damage and enhancing process efficiency.

The concept of engineering quasi-BIC states in metasurfaces to facilitate photocatalysis exemplifies the convergence of photonics and catalysis, leveraging wave-matter interactions for chemical control at the nanoscale. By translating this fundamental physics insight into a practical device architecture, the Tsinghua team has established a versatile platform that could be extended to diverse catalytic and sensing applications demanding high spatiotemporal precision.

In sum, the research showcases a compelling instance where advanced materials design, nanophotonics, and surface chemistry intersect to address longstanding challenges in reactive oxygen species generation. The quasi-BIC metasurface paradigm not only provides a robust solution for the rapid generation of singlet oxygen at therapeutic scales but also introduces a new dimension of control and efficiency that could redefine the capabilities of photodynamic therapy and beyond.

The publication in Light: Science & Applications stands as a testament to these interdisciplinary achievements. As the authors highlight, “BIC-engineered metasurfaces offer a generalizable route for efficient photon-to-chemical conversion at solid–liquid interfaces, unlocking immediate opportunities in photodynamic therapy, selective oxidation, and microreactor technologies where both low light dose and geometric precision are paramount.”

This pioneering work opens the door to further exploration of BIC and quasi-BIC states in nanophotonic structures tailored for catalytic applications, signaling a shift towards engineered nanoscale systems that harness light with exquisite control for biomedical and chemical innovations.

Subject of Research: Nanoscale photonics, photocatalysis, and photodynamic therapy.

Article Title: Quasi-BIC metasurfaces enable rapid, localized singlet-oxygen generation

News Publication Date: 2026 (exact date not specified)

Web References: DOI 10.1038/s41377-026-02267-9

Image Credits: Xing Fu et al.

Deep within our planet lies a critical interface known as the core–mantle boundary (CMB), a region where extreme temperatures and dynamic processes converge to shape Earth’s thermal and magnetic evolution. Recent research has illuminated the intricate behaviors of heat flow at this boundary, revealing how variations here influence the geodynamo—the mechanism responsible for Earth’s magnetic field. A groundbreaking study now explores how distinctive structures in the lowermost mantle can actually reverse the expected direction of heat transfer, fundamentally altering our understanding of how the deep Earth operates.

The core’s heat output and the mantle’s behavior are intimately linked, but spatial and temporal variations in heat flux at the CMB complicate this relationship. Heat flow from the core into the mantle typically fuels convective currents in the liquid outer core, driving the geodynamo process that sustains Earth’s magnetic shield. However, recent sophisticated simulations suggest that beneath certain geological features in the mantle, heat might instead flow back toward the core, a phenomenon previously unconfirmed and challenging conventional geophysical assumptions.

Central to this discovery are large low-shear-wave-velocity provinces (LLSVPs), massive structures located at the base of the mantle. These provinces are identifiable by their diminished seismic wave speeds, which geophysicists interpret as reservoirs of anomalously hot, chemically distinct materials. The new study models these LLSVPs with enhanced thermal conductivity adjustments and accounts for excess internal heating, simulating how these features interact dynamically with heat flow near the CMB.

The simulations reveal a striking phenomenon: heat flux directly beneath LLSVPs can be locally negative. This means, counterintuitively, that heat is being transferred from the mantle back into the core. This unexpected reversal challenges prior models which generally assumed a consistent outward flow of heat from core to mantle. Such negative fluxes have profound implications not only for the thermal balance of the Earth’s interior but also for the longevity and variability of its magnetic field.

Moreover, the research underscores that throughout the base of the mantle piles associated with LLSVPs, the heat flux remains lower than the adiabatic heat flux of the core. This thermal configuration suggests a degree of regional stratification at the top of the core, potentially explaining discrepancies observed in seismic and geomagnetic data. In other words, the topmost layer of the core may be thermally segregated in ways that we had not confirmed previously.

Interestingly, the study also explores the impact of subducted slabs—denser fragments of oceanic lithosphere—that eventually reach the CMB. The arrival of these slabs triggers pronounced spikes in heat flux, dramatically increasing the heterogeneity of lateral heat flow along the core–mantle boundary. This dynamic enhances the complexity of heat exchange patterns and further influences the geodynamo’s behavior, potentially affecting geomagnetic activity on geological timescales.

A significant implication of these findings relates to so-called “superchrons,” intervals lasting tens of millions of years during which Earth’s magnetic field remains stable without reversals. The occurrence of locally negative heat flux beneath the LLSVPs might explain these long periods of geomagnetic quiescence. When heat flows reversely into the core, it can alter convection patterns in ways that suppress the typical polarity flip mechanism, shedding new light on the origin and cessation of superchrons.

The study’s approach involved advanced mantle thermochemical convection modeling that incorporates temperature-dependent thermal conductivity and internal radiogenic heating within dense mantle piles. This methodological innovation provides a more realistic representation of the mantle’s behavior at extreme conditions than previous models, enabling researchers to capture subtle but critical feedbacks influencing heat fluxes at depth.

By reconciling seismic data, which reveals complex structures in the lowermost mantle, with geomagnetic observations that hint at temporal variability in the geodynamo, this research bridges a vital gap in Earth sciences. The correspondence between the spatial extents of LLSVPs and anomalies in the geomagnetic field suggests a coupling mechanism mediated through heat flux variations being directly tied to mantle dynamics.

The nuanced understanding of heat flow gleaned from this work also carries implications for the planet’s thermal evolution over geologic time. How heat migrates across the CMB influences the cooling rate of the core, the crystallization of the solid inner core, and consequently the lifecycle of the geodynamo. The discovery that heat transfer is not unidirectional, but can locally reverse in space and time, necessitates revisiting models of Earth’s deep thermal history and magnetic field generation.

This revelation also lays groundwork for interpreting seismic tomography results with a new lens, appreciating that chemical and thermal heterogeneity in LLSVPs exerts a tangible impact on core processes. The presence of chemically distinct reservoirs affects not only the mantle’s physical properties but also its thermal gradient with direct knock-on effects for core convection patterns and magnetic field intensity.

Such interconnectedness across Earth’s deep interior underscores the planetary-scale complexity of thermal and compositional interactions driving Earth’s long-term stability. The core-mantle boundary emerges not simply as a static physical barrier but as a dynamic interface where thermal regimes, chemical signatures, and fluid motion all coalesce to modulate our planet’s magnetic heartbeat.

Future research building on these findings may sharpen our forecasts for geomagnetic field behavior, including its reversals and excursions, by incorporating the interplay of mantle structures and heat flux heterogeneity shown in this study. Understanding these processes is not merely academic; Earth’s magnetic field shields life on the surface from charged solar particles, making geomagnetic stability crucial for habitability.

In conclusion, the discovery of negative heat flux beneath LLSVPs represents a paradigm shift in understanding Earth’s deep thermal dynamics. It opens fresh avenues into interpreting Earth’s magnetic field history and its deep interior’s energy budget, challenging geoscientists to refine their models of the planet’s evolving mantle and core mechanisms. The study invites a reconsideration of how internal heat governs the interplay between mantle convection and geomagnetic phenomena, securing a pivotal advance in the geophysical sciences.

As our planet continues its ceaseless churn beneath the crust, these findings remind us that Earth’s interior is a realm of profound complexity and subtle interactions. The dance of heat and composition at the core-mantle boundary not only choreographs magnetic field generation but ultimately shapes the environment that sustains life above ground. Unlocking its secrets brings us closer to comprehending the planet’s past, present, and future in extraordinary detail.

Subject of Research: Core–Mantle Boundary Heat Flux Variations and Their Impact on Mantle Dynamics and Geodynamo Behavior

Article Title: Negative core–mantle boundary heat flux beneath low-shear-wave-velocity provinces

Article References:
Deschamps, F., Guerrero, J.M., Amit, H. et al. Negative core–mantle boundary heat flux beneath low-shear-wave-velocity provinces. Nat. Geosci. (2026). https://doi.org/10.1038/s41561-026-02018-w

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41561-026-02018-w

In a remarkable advancement that promises to redefine materials science, researchers have developed an extraordinary crystal exhibiting isotropic zero thermal expansion (ZTE) across an unprecedentedly wide temperature range. This pioneering work focuses on a sodalite-structured compound, Cd4Al6O12SO4, abbreviated as CASO, which maintains near-perfect dimensional stability from cryogenic temperatures as low as 11 K up to an exceptional 893 K. Such a feat addresses one of the most persistent challenges in materials engineering—achieving consistent, isotropic ZTE behavior over a broad thermal window, well beyond the typical operating limit of 400 K commonly found in existing materials.

Thermal expansion, the tendency of materials to expand or contract in response to temperature changes, significantly influences the reliability and precision of components in advanced technological systems. This is particularly critical in optics, aerospace, and microelectronics, where slight dimensional deviations can lead to catastrophic failures or degraded performance. Traditionally, materials exhibiting zero or near-zero thermal expansion either operate within narrow temperature bands or display anisotropic expansion, complicating their practical application. CASO emerges as a groundbreaking solution by combining flexibility and robustness within a closed-framework sodalite structure, a geometry celebrated for its remarkable stability.

What sets CASO apart is the ingenious incorporation of flexible interstitial groups realized via fractionally occupied atoms nestled within the sodalite framework. This strategic design introduces subtle positional disorder among ligand atoms, a feature that amplifies transverse atomic vibrations responsible for generating negative thermal expansion. These enhanced transverse vibrations effectively counterbalance the intrinsic positive thermal expansion that arises from atomic lattice expansion at elevated temperatures. As a result, CASO achieves a finely tuned, cancellatory interplay between positive and negative thermal expansion mechanisms, yielding an overall coefficient of thermal expansion measured at a negligible 0.21(23) × 10^−6 K^−1.

The research team’s exploration of CASO’s structural integrity under rigorous thermal cycling reveals impressive resilience, with the material maintaining its crystalline structure up to 1,100 K. This high thermal threshold expands the operational capacity of ZTE materials into regimes previously inaccessible, paving the way for applications in extreme thermal environments such as space exploration technologies and high-temperature sensor systems. Importantly, the integrity of CASO at such elevated temperatures also suggests potential advancements in engineering components that must endure thermal shocks without suffering deformation or failure.

Beyond mechanical stability, CASO exhibits a solar-blind ultraviolet (UV) transparency window extending down to 275 nm. This optical property signifies that the material can transmit UV light within this range without absorption, rendering it valuable for specialized UV optics and photonics applications. Devices requiring minimal optical noise and high stability, such as spaceborne UV detectors and precision laser optics, stand to benefit from CASO’s unique optical-transparency combined with its unparalleled thermal stability.

Optical materials are notoriously susceptible to thermal fluctuations, which induce refractive index changes and distort beam paths, complicating precision measurements and laser operations. CASO’s thermally induced optical fluctuations are at least twice as low as those found in conventional optical media, an achievement that underscores its potential to revolutionize precision optics. This property not only enhances the performance of existing systems but also reduces the need for complex compensatory mechanisms, simplifying designs and improving reliability in challenging thermal environments.

Substantially, CASO’s isotropic ZTE capacity challenges and expands the conventional understanding of thermomechanical behavior in framework materials. The sodalite structure itself provides a three-dimensional network that constrains thermal responses isotropically, a feature critical for applications demanding uniform response in all spatial directions. The partial occupation and flexibility of interstitial species suggest new dimensions of control over lattice dynamics and open pathways for tailored ZTE behavior through chemical modification and structural engineering.

The discovery underscores the significance of lattice dynamics modulation via controlled disorder—a concept that holds promise far beyond ZTE materials. Manipulating atomic vibrational modes through fractional occupancy and positional disorder reshapes how scientists can exploit negative thermal expansion while mitigating positive expansion, with implications for diverse fields from thermal barrier coatings to quantum materials.

Moreover, the work by Liu, Jiang, Molokeev, and colleagues establishes a universal strategy for engineering ZTE materials, thus serving as a blueprint for future crystal design. Rather than relying on complex composites or layered heterostructures, this approach leverages the intrinsic vibrational characteristics and flexibility within single-phase crystals. Such simplicity in design may accelerate industrial adoption and reduce costs associated with fabricating advanced thermal-stable materials.

The implications of this discovery are profound for the electronics and precision engineering industries. Components fabricated from CASO could maintain micron-scale tolerances across vast thermal gradients, thereby improving the longevity and performance of microelectromechanical systems (MEMS), precision optics, and high-frequency electronic devices. The broad temperature stability and isotropy also alleviate challenges associated with thermal mismatch and interface stresses in multilayered devices.

In addition to immediate technological applications, CASO’s unique properties may spur new scientific inquiries into the fundamental physics of thermal expansion. Investigating how flexible ligand atoms interact within complex frameworks provides insights into phonon dynamics, anharmonic lattice vibrations, and thermodynamic stability. This research advances theoretical models and computational simulations aiming to predict and control thermal properties at the atomic scale.

As society increasingly demands materials that withstand extreme environmental conditions without compromising structural or optical performance, CASO stands as a beacon of hope and innovation. Its extended temperature operational window combines mechanical robustness, optical transparency, and thermal stability into a single crystalline phase—attributes that are rarely coexistent. This convergence could lead to breakthroughs in harsh-environment sensors, satellite optics, and next-generation aerospace components.

Furthermore, the concept of embedding fractionally occupied flexible groups within stable frameworks could be extrapolated to customize other physical properties such as thermal conductivity, dielectric constants, and even magneto-thermal behavior. This multifunctionality potential situates CASO not just as a material of the present, but as a foundation for multifunctional crystals engineered at the atomic level for bespoke applications.

In conclusion, CASO embodies a paradigm shift in thermal expansion control, marrying structural ingenuity with atomic-scale dynamism. Its validation as an isotropic zero thermal expansion material from cryogenic to near-1100 K temperatures resolves a longstanding challenge and invites a new era of functional materials science. This elegant interplay of lattice architecture and vibrational physics heralds a future where materials no longer passively endure thermal fluctuations but actively neutralize them, ushering in unprecedented precision and resilience in advanced technologies.

Such groundbreaking discoveries, as reported by Liu and colleagues in Nature Chemistry, showcase the transformative power of crystal engineering and vibrational control. The research propels us beyond incremental advances to a realm where materials can be custom-tuned for the harshest and most demanding environments known to science and industry, reshaping what is possible across technological frontiers.

Subject of Research: Isotropic zero thermal expansion properties in a sodalite-structured crystal (Cd4Al6O12SO4, CASO) across an exceptional temperature range.

Article Title: Isotropic zero thermal expansion in sodalite crystals from 11 to 893 K.

Article References:
Liu, Y., Jiang, X., Molokeev, M.S. et al. Isotropic zero thermal expansion in sodalite crystals from 11 to 893 K. Nat. Chem. (2026). https://doi.org/10.1038/s41557-026-02174-x

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41557-026-02174-x