Efficient and selective excitation of lattice vibrations is central to controlling energy flow at the nanoscale, yet remains challenging under conventional optical excitation. Here, we introduce a mid-infrared-assisted phonon amplification approach, termed MIRAPA, that enables efficient energy injection directly into vibrational bonds. Using surface-enhanced resonant Raman scattering in few-layer MoS_2, we exploit strong exciton–phonon coupling to monitor phonon populations. When mid-infrared (MIR) light is introduced, it couples directly to out-of-plane lattice vibrations, leading to room-temperature phonon amplification exceeding 80%. Crucially, MIRAPA bypasses electronic excitation pathways, allowing the MIR power density to be nearly 300× lower than that required for visible excitation to achieve comparable enhancement. The resulting phonon modulation is robust, persisting over more than 2800 on/off cycles and exceeding 15 hours of continuous-wave laser illumination without degradation. Quantitative analysis yields an effective noise-equivalent power of approximately 0.3 nW/√(Hz) for MIR detection, highlighting the sensitivity of the approach. By combining vibrational selectivity, low-power operation, and long-term stability, MIRAPA provides a robust platform for probing and amplifying phonons in two-dimensional semiconductors. These results open new opportunities for nanoscale vibrational sensing, mid-infrared detection, and phonon-based coherent devices, including routes toward phonon lasing.

Förster energy transfer underpins modern photonics, yet establishing an analogous vibrational pathway in the mid-infrared (MIR) remains highly challenging, as sub-picosecond intramolecular vibrational redistribution (IVR) suppresses intermolecular coupling. Here we demonstrate vibrational donor–acceptor transfer in the MIR and subsequent upconversion to visible luminescence enabled by sub-2 nm plasmonic nanogaps. The extreme lateral field confinement in metal–molecule–metal ring cavities defined by self-assembled molecular spacers couples efficiently to in-plane molecular dipoles. Continuous-wave MIR excitation selectively populates -C≡N vibrational donors, and plasmon-enhanced near-field coupling transfers this energy to nearby electronic acceptors, generating anti-Stokes visible emission under low power densities. Upconversion efficiencies exceeding 0.3% are observed, limited by competition between the plasmon-mediated transfer rate and IVR. These results show that extreme plasmonic confinement can redirect molecular vibrational relaxation pathways, opening a route toward vibrational nanophotonics, intermolecular interactions for bioimaging, and room-temperature MIR detection based on molecular degrees of freedom.

High-refractive-index materials underpin a wide range of optical technologies, including communications, imaging, lasers, and integrated photonic systems. Here, we demonstrate a self-assembled metamaterial platform based on gold nanoparticle aggregates with nanometer-scale gaps exhibit remarkably high effective refractive indices exceeding 15 in the mid-infrared regime, while simultaneously producing gap-field enhancements of at least two-orders of magnitude. This combination of high refractive index and extreme field enhancement enables exceptionally strong light-matter interactions. We demonstrate this by designing a compact high-index metamaterial device supporting an anapole, which further enhances the nanogap field. By placing quantum emitters with terahertz transitions inside the plasmonic gaps, we show a stimulated-emission response enhanced by at least three orders of magnitude, highlighting applications in non-linear optics, frequency up-conversion and vibrational strong coupling.

Chiroptical spectroscopic techniques offer a nondestructive means of elucidating the stereochemical structures of biomolecules and have demonstrated significant applications across diverse fields, including bioscience, biomedicine, and clinical diagnosis, among others. However, the inherently weak chiroptical effects exhibited by natural chiral molecules pose a significant challenge to detection sensitivity. In this study, we demonstrate an ultrasensitive ultraviolet chiral plasmonic biosensor (CPB) that leverages a self-assembled metasurface composed of passivated aluminum chiral shells (ACSs). By meticulously optimizing the geometry and size of these shells, we achieve a uniform, large, and readily accessible superchiral field on the top surface of the ACSs, thereby enhancing their interaction with chiral biomolecules. In addition, the abundant surface lattice resonance (SLR) modes excited in the ultraviolet waveband narrow the chiroptical resonance peaks and improve the identifiability of sensor pointers. In experiments, large-area ACSs with strong chiroptical effects were realized by depositing Al on a colloidal monolayer with hexagonal order and then passivating it with ozone to improve stability. When immersed in solutions containing chiral molecules, the g-factor maxima of the ACSs exhibit a notable peak shift that correlates with both the stereochemical structures and the concentrations of the biomolecules. Notably, the consistency chiral sensor parameter U reaches 10.9095 for the null point and 0.1739 for peaks of g-factor spectra, which makes a record in the field CPBs. The systematic analysis of the SLR modes, superchiral field, and chiral sensor parameters further rationalizes the record chiral sensor performance realized in this work.

Metal nanocrystals synthesized in achiral environments usually exhibit no chiroptical effects. However, by placing nominally achiral nanocrystals 1.3 nm above gold films, we find giant chiroptical effects, reaching anisotropy factors as high as g ≈ 0.9 for single nanodecahedra placed on a gold mirror (NDoM). We show that this is a general phenomenon depending on the geometry, demonstrating it for various nanocrystal shapes. Theoretical modeling reveals that tiny chiral imperfections are strongly enhanced by edge modes in the gap, which coherently superpose with in-plane dipoles to generate strong chiroptical signatures. This phenomenon results in photonic spin Hall effects and distinctive chiral scattering patterns.

Conjugated polymers are promising material candidates for many future applications in flexible displays, organic circuits, and sensors. Their performance is strongly affected by their structural conformation including both electrical and optical anisotropy. Particularly for thin layers or close to crucial interfaces, there are few methods to track their organization and functional behaviors. Here we present a platform based on plasmonic nanogaps that can assess the chemical structure and orientation of conjugated polymers down to sub-10 nm thickness using light. We focus on a representative conjugated polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), of varying thickness (2-20 nm) while it undergoes redox in situ. This allows dynamic switching of the plasmonic gap spacer through a metal-insulator transition. Both dark-field (DF) and surface-enhanced Raman scattering (SERS) spectra track the optical anisotropy and orientation of polymer chains close to a metallic interface. Moreover, we demonstrate how this influences both optical and redox switching for nanothick PEDOT devices.

Tightly confined plasmons in metal nanogaps are highly sensitive to surface inhomogeneities and defects due to the nanoscale optical confinement, but tracking and monitoring their location is hard. Here, we probe a 1-D extended nanocavity using a plasmonic silver nanowire (AgNW) on mirror geometry. Morphological changes inside the nanocavity are induced locally using optical excitation and probed locally through simultaneous measurements of surface enhanced Raman scattering (SERS) and dark-field spectroscopy. The increasing molecular SERS intensity and corresponding redshift of cavity plasmon modes by up to 60 nm indicate atomic-scale changes inside the nanocavity. We correlate this to diffusion of silver atoms into the nanogap, which reduces the nanogap size and enhances the optical near-field, enhancing the SERS. These induced changes can be locally excited at specific locations along the length of the nanowire and remain stable and nonreversible. Polymer surface coating on the AgNW affects the power threshold for inducing atom migration and shows that strong polyvinylpyrrolidone (PVP)- Ag binding gives rise to higher power thresholds. Such extended nanogap cavities are an ideal system to provide robust SERS while withstanding high laser powers. These results provide insights into the inhomogeneities of NW nanocavities and pave the way toward spatially controlled NW lithography in ambient conditions.

The strong-coupling interaction between quantum emitters and cavities provides the archetypical platform for fundamental quantum electrodynamics. Here we show that methylene blue (MB) molecules interact coherently with subwavelength plasmonic nanocavity modes at room temperature. Experimental results show that the strong coupling can be switched on and off reversibly when MB molecules undergo redox reactions which transform them to leuco-methylene blue molecules. In simulations we demonstrate the strong coupling between the second excited plasmonic cavity mode and resonant emitters. However, we also show that other detuned modes simultaneously couple efficiently to the molecular transitions, creating unusual cascades of mode spectral shifts and polariton formation. This is possible due to the relatively large plasmonic particle size resulting in reduced mode splittings. The results open significant potential for device applications utilizing active control of strong coupling.

A single light-emitting dye molecule precisely placed within the tiny gap of a metal nanodimer boosts light-matter coupling - a step closer to the development of quantum devices operating at room temperature.

Plasmonic nanoantennas can focus light at nanometer length scales providing intense field enhancements. For the tightest optical confinements (0.5-5 nm) achieved in plasmonic gaps, the gap spacing, refractive index, and facet width play a dominant role in determining the optical properties making tuning through antenna shape challenging. We show here that controlling the surrounding refractive index instead allows both efficient frequency tuning and enhanced in-/output coupling through retardation matching as this allows dark modes to become optically active, improving widespread functionalities.

Organophosphates and their derivatives are deadly compounds owing to their ability to disrupt key regulators of biological activity and neuronal transmission. As such, typical uses for synthetic and natural organophosphates include nerve agents and toxic pesticides. Organophosphate pesticides alone are estimated to make up around 3-10 % of the international pesticide poisoning deaths, or approximately 5-15,000 deaths annually. Mechanistically, they irreversibly bind to acetylcholinesterase, a crucial enzyme dealing with motor control that has minimal structural differences across all walks of life explaining the universal toxicity of organophosphates. In this study, we present the fabrication of a nanoparticle-based detection method to detect two commonly used organophosphates: dimethyl methylphosphonate (DMMP) which is used as the starting material for many chemical warfare agent syntheses, and dimethyl chlorophosphate (DMCP) which is a potent acetylcholinesterase inhibitor and readily harmful to the body through dermal absorption or ingestion. We further demonstrate accurate and precise micromolar detection of these organophosphates with a simple portable Raman spectrometer, and additionally demonstrate the ability to easily detect and distinguish between both analytes in a heterogenous solution using this methodology. The nanoparticle-based detection relies on a method of Surface-enhanced Raman spectroscopy (SERS) in liquid phase. Throughout the duration of the experiment, liquid solutions and a portable Raman spectrometer were utilized to demonstrate efficacy of the detection method even with instruments and conditions that would be typically seen in the environment of organophosphate use, such as in a less technology developed warfare or rural setting. Through this detection method, we found a reliable finger-print peak for DMMP (710.63 cm(-1)) with a limit of detection (LOD) of 9.11 mM and a limit of quantitation (LOQ) of 27.6 mM, with 1.5 +/- 0.11 SERS. Similarly, for DMCP (755.97 cm(-1)), a LOD of 17.79 mM, a LOQ of 53.90 mM, and 1.3 +/- 0.01 SERS enhancement were observed. Our theoretical studies predict possible SERS enhancement of >10(4), with significantly stronger signal compared with spherical nanoparticles. Time and pH studies show that our detection method is both fast and facile, without any required field modifications for baseline detection.

Room-temperature detection of molecular vibrations in the mid-infrared (MIR, λ = 3–30 µm) has numerous applications, including real-time gas sensing, medical imaging and quantum communication. However, existing technologies rely on cooled semiconductor detectors because of thermal noise limitations. One way to overcome this challenge is to upconvert the low-energy MIR photons into high-energy visible wavelengths ( λ = 500–800 nm) where detection of single photons is easily achieved using silicon technologies. This process suffers from weak cross-sections and the MIR-to-visible wavelength mismatch, limiting its efficiency. Here we exploit molecular emitters possessing both MIR and visible transitions from molecular vibrations and electronic states, coupled through Franck–Condon factors. By assembling molecules into a plasmonic nanocavity resonant at both MIR and visible wavelengths, and optically pumping them below the electronic absorption band, we show transduction of MIR light. The upconverted signal is observed as enhanced visible luminescence. Combining Purcell-enhanced visible luminescence with enhanced rates of vibrational pumping gives transduction efficiencies of >10%. MIR frequency-dependent upconversion gives the vibrational signatures of molecules assembled in the nanocavity. Transient picocavity formation further confines MIR light down to the single-molecule level. This allows us to demonstrate single-molecule MIR detection and spectroscopy that is inaccessible to any previous detector.

Strong coupling of molecular vibrations with light creates polariton states, enabling control over many optical and chemical properties. However, the near-field signatures of strong coupling are difficult to map as most cavities are closed systems. Surface-enhanced Raman microscopy of open metallic gratings under vibrational strong coupling enables the observation of spatial polariton localization in the grating near field, without the need for scanning probe microscopies. The lower polariton is localized at the grating slots, displays a strongly asymmetric line shape, and gives greater plasmon-vibration coupling strength than measured in the far field. Within these slots, the local field strength pushes the system into the ultrastrong coupling regime. Models of strong coupling which explicitly include the spatial distribution of emitters can account for these effects. Such gratings enable exploration of the rich physics of polaritons, its impact on polariton chemistry under flow conditions, and the interplay between near- and far-field properties through vibrational polariton-enhanced Raman scattering.

Developing highly enhanced plasmonic nanocavities allows direct observation of light-matter interactions at the nanoscale. With DNA origami, the ability to precisely nanoposition single-quantum emitters in ultranarrow plasmonic gaps enables detailed study of their modified light emission. By developing protocols for creating nanoparticle-on-mirror constructs in which DNA nanostructures act as reliable and customizable spacers for nanoparticle binding, we reveal that the simple picture of Purcell-enhanced molecular dye emission is misleading. Instead, we show that the enhanced dipolar dye polarizability greatly amplifies optical forces acting on the facet Au atoms, leading to their rapid destabilization. Using different dyes, we find that emission spectra are dominated by inelastic (Raman) scattering from molecules and metals, instead of fluorescence, with molecular bleaching also not evident despite the large structural rearrangements. This implies that the competition between recombination pathways demands a rethink of routes to quantum optics using plasmonics.

Chiral metamaterials (CMs) composed by artificial chiral resonators have attracted great attentions in the recent decades due to their strong chiroptical resonance and identifiable interaction with chiral materials, facilitating practical applications in chiral biosensing, chiral emission, and display technology. However, the complex geometry of CMs improves the fabrication difficulty and hinders their scalable fabrication for practical applications, especially in the visible and ultraviolet wavelengths. One potential strategy is the colloidal lithography that enables parallel fabrication for scalable and various planar structures. Here, we demonstrate a stepwise colloidal lithography technique that uses sequential deposition from multiple CMs and expand their variety and complexity. The geometry and optical chirality of building blocks from single deposition are systematically investigated, and their combination enables a significant extension of the range of chiral patterns by multiple-step depositions. This approach resulted in a myriad of complex designs with different characteristic sizes, compositions, and shapes, which are particularly beneficial for the development of nanophotonic materials. In addition, we designed a flexible chiral device based on PDMS, which exhibits a good CD value and excellent stability even after multiple inward and outward bendings. The excellent compatibility to various substrates makes the planar CMs more flexible in practical applications in microfluidic biosensing.

In recent years, it has become evident that Systemic Lupus Erythematosus (SLE) is a disease characterized by an array of autoantibodies directed against the native nucleosome, its DNA component and/or its histone component. Nuclear antigens are generated and released in vivo during apoptosis. A hallmark of apoptosis is the cleavage of chromatin by caspase-activated DNase. This fragmentation occurs at the internucleosomal level and leads to DNA ladder formation classically associated with apoptosis. Thus, dysregulation of DNA fragmentation might be directly linked to the induction of autoimmunity in SLE. In our studies, activated human lymphoblasts contain high amounts of core histones in their cell lysates after apoptosis induction. This accumulation correlated highly with markers of early apoptosis (Annexin V positive, propidium iodide negative), but not with markers of late apoptosis or necrosis. Interestingly, accumulation of core histones or nucleosomes in cell lysates was detected as early as 30 or 60 min after UV irradiation, whereas phosphatidylserine externalization occurred 2 hr after apoptosis induction. Our results suggest that extranuclear accumulation of core histones is a very early event in apoptosis, preceding the externalization of phagocytosis signals on the outer membrane surface of apoptotically dying lymphoblasts. The following review will discuss these results in a broader perspective which includes our hypothesis of how apoptosis dysregulation during early phases may contribute to the induction of autoimmunity against nuclear autoantigens as seen in SLE.

Low-cost and large-area chiral metamaterials (CMs) are highly desirable for practical applications in chiral biosensors, nanophotonic chiral emitters, and beyond. A promising fabrication method takes advantage of self-assembled colloidal particles, onto which metal patches with defined orientation are created using glancing angle deposition (GLAD). However, using this method to make uniform and well-defined CMs over macroscopic areas is challenging. Here, we fabricate a uniform large-area colloidal particle array by interface-mediated self-assembly and precisely control the structural handedness of chiral plasmonic shells (CPSs) using GLAD. Strong chiroptical signals arise from twisted currents at the main, corner, and edge of CPSs, allowing a balance between strong chiroptical and high transmittance properties. Our shell-like chiral geometry shows excellent sensor performance in detecting chiral molecules due to the formation of uniform superchiral fields. Systematic investigations optimize the interplay between peak and null point resonances in different CPSs and result in a record consistency chiral sensor parameter U, i.e., 3.77 for null points and 0.0867 for peaks, which are about 54 and 1.257 times larger than the highest value (0.068) of previously reported CMs. The geometrical chirality, surface plasmonic resonance, chiral surface lattice resonance, and chiral sensor performance evidence the chiroptical effect and the excellent chiral sensor performance.