Recently, Quzhou Aurantii Fructus Extract (QAFE) was reported to exert anti-inflammatory effects on different types of respiratory diseases; however, it is yet to be determined whether it is effective in patients with idiopathic pulmonary fibrosis (IPF). The purpose of this study is to explore the capacity of QAFE to fight fibrotic disease, in particular how it works in relation to the regulation of the nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase 1 (HO-1) pathway. QAFE was made with Quzhou Fructus Aurantii (QAF), and the content of four flavonoids in the samples prepared was analyzed by high-performance liquid chromatography (HPLC). The therapeutic effect of QAFE was experimented by establishing IPF models in mice and in cells. Identification of the mechanism of QAFE in IPF through knockout or knockdown of the Nrf2 gene. The experiments suggest that QAFE has the potential to prevent IPF-induced inflammation, collagen deposition, oxidative stress, and apoptosis of cells. Silencing Nrf2 by knockdown or knockout is enough to prevent the capacity of QAFE to inhibit the process of inflammation, oxidative stress, and collagen deposition to cause more serious lung injury and HO-1 expression downregulation. QAFE is a potential new antifibrotic drug in IPF with an effect on the Nrf2/HO-1 pathway that reduces inflammation and oxidative stress.

Chirality, the absence of mirror symmetry, defines matter interactions and properties at all scales, with significant implications in fields spanning nanotechnology, pharmaceuticals, and agrochemicals. Circular dichroism (CD), the differential absorption of circularly polarized light of different handedness in chiral media, characterizes chirality. Here, we apply a photo-acoustic spectroscopy (PAS) as a scattering-free method for characterizing absorption and CD. We investigate asymmetric silver-based metasurface in a broad spectral range; we show CD dependence on the incident angle and modulation frequency. We then use optimal wavelength-angle points to perform spatial mapping of CD, which shows perspective in surface CD and uniformity characterization.

Alessandro Belardini, a great professor, mentor and scientist, prematurely passed away on 9 February 2026, shortly after his 54th birthday. He is deeply missed in both Italian and International community of plasmonics and nanophotonics, for both research and teaching, and for his infinite kindness, patience, and support of the young peers. To his students, he was a Renaissance man, answering questions with dedication and depth, willing to help with empathy. To his research colleagues, his nonlinear and chiro-optical experiments led to pioneering contributions in chiro-optical research at the nanoscale. Moreover, he was dedicated to the mission of the European Optical Society, its Italian branch, and the Plasmonica working group in plasmonics and nano-photonics. Behind more than 100 highly impactful research articles and proceedings, there is his name, efforts and dedication. However, as we were privileged to directly work and learn from him, in this memoriam article we would like to remember him for his personal virtues, and skills he had as a professor, supervisor and mentor.

Plasmonic systems are typically characterized by a trade-off between sub-wavelength field confinement and dissipative losses that limit the Q -factor of optical resonances. In this work, we study chiral quasi-bound states in the continuum (q-BICs) in a metallic nanohole array with broken-symmetry holes, focusing on the role of losses in a wide spectral range for the q-BIC resonance frequency. We disentangle the contributions of radiative vs ohmic losses to the Q -factor, showing that both of them are reduced at longer resonance wavelengths, and relating this behavior to the change in field confinement. As a result of the reduction of both kinds of losses, we demonstrate that high circular dichroism, high Q -factor, and strong local-field enhancement can be simultaneously achieved; therefore, the chiral q-BIC investigated here effectively breaks the trade-off between field confinement and losses. The results can be exploited to realize high-Q chiral resonances with enhanced radiation-matter interaction.

Photo-acoustic spectroscopy is a powerful photo-thermal method for scattering-free, contactless and non-destructive measurements of absorption. In plasmonics and nano-photonics, it allows for characterization of light-matter interactions leading to non-radiative relaxation processes, which generate heat. Here, we address the issue of detecting absorption signal of periodically nanostructured layer of gold, sitting on a commercial, absorbing substrate. The nanostructured plasmonic layer alone exhibits resonant peaks in the near-infrared range due to a 2D array of elliptical nanoholes in Au. The substrate itself has cavity interference resonances in the same range, due to a layer of Si3N4 on Si wafer. Conventional optical techniques are influenced by scattering, which complicates the characterization of the nanostructures’ absorption against the properties of the substrate. We apply photo-acoustic technique with a widely tunable laser source to measure the absorption spectra of these geometries, as well as on an Au-covered substrate without nanoholes and on a bare Si substrate. A microscope enabled us to differentiate the nanohole response from its surroundings, while the tunable modulation frequency allowed for studying different absorption depths. Complementary optical simulations reveal the spatial distribution of absorption, in good agreement with experimental results. A major potential of the proposed approach lies in monitoring and discriminating nanoscale structural changes in thin absorbing layers against the strongly absorbing substrate background, which is of great importance in situations involving sensing of low quantity of absorbing material placed on commercial wafers. Moreover, besides resonant plasmonic effects, this photo-acoustic set-up and modelling can be further adapted to study light coupling with plasmonic nanohole arrays in terms of incident light angle of incidence and polarization.

Chirality an intrinsic property of certain entities in the universe, is characterized by the absence of mirror symmetry and plays a crucial role in molecular interactions and properties. Circular dichroism (CD), measured using circulary polarized light, is an important method for chirality characterization. In this study, using a photo-acoustic spectroscopy (PAS), it allows direct measurement of local absorption, by monitoring the heat produced and transferred to the surrounding air, regardless the transmitted, reflected, and scattered light that ows away from the sample. Using a widely tunable laser source in the near-infrared and visible ranges, our PAS system incorporates numerous adjustable parameters, including wavelength, polarization, incidence angle, modulation frequency, and spatial positioning via translational and rotational stages. This set-up allows for precise spatial and spectral mapping of absorption and CD, enabling the study of extrinsic chirality in nanostructured metasurfaces, potentially addressing also important issues on homogeneity of the nanostructures, size of the domains and their orientation. These findings highlight the versatility and sensitivity of PAS for advanced chiral analysis, offering new insights into the optical behavior of nanostructures and paving the way for broader applications in nanophotonics and plasmonics.

We theoretically demonstrate that Bound States in the Continuum (BICs) can appear in plasmonic metasurfaces, specifically in a metal nanohole array with broken symmetry, and can be exploited to yield a strong chiral response with high Q-factor and local field enhancement. When the nanoholes are filled with a medium supporting a Lorentz-like resonance, the interaction between the quasi-BIC and the active medium can gives rise to strongly coupled hybrid modes, which represent chiral polariton BICs in the plasmonic system.

The strong-coupling regime of light-matter interaction is a peculiar situation in which a photonic-like and a matter-like excitation are coupled to form mixed quasiparticles, which share the properties of their constituents. In this work, we report the prediction of chiral optical response in the strong coupling regime, produced by a plasmonic bound state in the continuum (BIC) coupled with an active medium. We consider a gold metasurface with oval nanoholes, which supports a quasi-BIC upon symmetry breaking. We introduce an active medium characterized by the Lorentz model, which allows tuning of the oscillator strength to achieve strong coupling between the quasi-BIC mode and the active medium's resonances. These strongly coupled modes - which we name plasmonic polariton BICs - become chiral at a finite angle of incidence, with nearly maximum circular dichroism (CD) in absorption and transmission. This new type of chiral plasmonic polariton BICs opens up a new approach for studying chiral phenomena in the strong coupling regime of light-matter interaction. This can be achieved by properly designed metasurfaces infused with colloidal quantum dots tuned to resonate with the quasi-BIC.

Chirality conferral is fundamental for understanding the origin of life, and it is of direct importance for synthesizing new pharmaceuticals in the face of growing antibiotic resistance. Human-made, self-assembling nanostructures replicate the biological chirality conferral processes utilizing covalent and non-covalent bonds. However, chirality conferral from one form of matter to another via electromagnetic fields is more subtle and less explored. Here we report chirality conferral between gold nanohelices and achiral molecules (crystal violet). This conferral enables the experimental observation of a physical effect predicted in 1979-hyper-Raman optical activity. To benefit from Fermi's golden rule, the chirality conferral system was designed as doubly resonant, with the nanohelices and molecules resonating at the fundamental frequency and at the second-harmonic, respectively. We provide a theoretical framework for our results that expands the original mathematical formalism to include surface-enhanced hyper-Raman scattering and the chirality conferral process. Our results demonstrate that field-driven chirality conferral mechanisms are opening up entire fields of research, as exemplified by the discovery of a physical phenomenon. Theoretically predicted in 1979, hyper-Raman optical activity is now experimentally observed through chirality conferral from the electromagnetic field of chiral plasmonic gold nanohelices to crystal violet molecules that are achiral, sparking new science at the organic-inorganic interface.

Tailoring nonlinear optical properties at the nanoscale is a hot topic in nowadays nanophotonics, promising for applications spanning from sensing to ultrafast optical communications. Here we present a numerical approach of designing a simple semiconductor nanostructure able to tailor second harmonic emission in the near- and far-field. We start from linear simulations of ZnO nanospheres, which reveal multipolar nature of the scattering. Next, we show how the same nanospheres, with radii in 30–130 nm range, excited at 800 nm, manipulate the directivity of the emitted second harmonic. We observe that the nanospheres which exhibit Kerker condition at 400 nm, emit the second harmonic field in the forward direction. We further investigate how the asymmetry (ellipsoid geometry) tailors the second harmonic directivity. We finally introduce geometry with low chiro-optical response, and observe that the second harmonic far-field depends on the handedness of the light exciting the nanostructure at 800 nm.

Nanosphere lithography is a cost- and time-efficient tool for the fabrication of various nanostructured materials. Multiple steps of metal layer deposition at different oblique angles were shown to produce complex asymmetric and chiral shapes. Here, we investigate samples in which polystyrene nanospheres are covered by Ag or combination of Ag and Au at a single step (under 45°). In this way, we obtain metasurfaces with asymmetric shells, with a nanohole array formed due to the shadowing effect. We investigate chiro-optical properties of four samples by exciting them in the 700-1000 nm range, at angles of incidence from -45° to +45°; we report on dissymmetry in the total extinction between left and right circularly polarized excitation gext, which follows the rules of extrinsic chirality. We then resolve the transmission of Ag metasurface in terms of hyperspectral Stokes parameters, and we connect the S3 parameter with gext. Finally, we characterize nanohole arrays obtained from the same samples when the nanospheres are removed; we further perform electromagnetic simulations to gain insight into the “egg” shaped nanohole.

VO2 is a promising phase change material offering a large contrast of electric, thermal, and optical properties when transitioning from semiconductor to metallic phase. Here we show that a hybrid metamaterial obtained by proper combination of a VO2 layer and a nanodisk gold array provides a tunable plasmonic gap resonance in the infrared range. Specifically, we have designed and fabricated a metal-insulator-metal gap resonance by inserting sub-wavelength VO2 film between a flat gold layer and a gold nanodisk resonator array. The resonance of the hybrid metamaterial is centered in the useful 3-5 mu m range when VO2 is in its semiconductor state. The experimental study highlights a monotonical spectral tuning of the resonance when increasing temperature up to 50 degrees C above the room temperature, providing a continuous resonance shift of almost 1 mu m in the mid-infrared range. Wavelength range and intensity tunability can be further optimized by modifying the thicknesses of the layers and metamaterial parameters.

Recently, novel chiroptical harmonic scattering effects were reported, and the associated techniques have emerged as promising tools for characterizing the chirality of light scatterers, randomly dispersed in isotropic liquids. So far, the associated new physical effects have only been demonstrated in a handful of materials. For each material, only one size distribution has been studied. While third-harmonic chiroptical scattering, in the Rayleigh regime, has previously been demonstrated from Ag nanohelices, the data were only collected for right-handed scattering, with respect to the wavevector of incident light. Here, we present third-harmonic chiroptical scattering from Ag nanohelices with larger dimensions than those studied before. Moreover, we provide data in both right-handed and forward scattering. Our data are consistent with hyper-Rayleigh scattering and demonstrate that the recorded signal follows a cubic law with respect to the illumination laser power. Additionally, the obtained third-harmonic ellipticities clearly distinguish between left- and right-handed Ag nanohelices. The results reported here contribute to establish the applicability of chiroptical harmonic scattering to scatterers with various sizes, randomly dispersed in isotropic liquids.

Chirality is omnipresent in the living world. As biomimetic nanotechnology and self-assembly advance, they too need chirality. Accordingly, there is a pressing need to develop general methods to characterize chiral building blocks at the nanoscale in liquids such as water-the medium of life. Here, we demonstrate the chiroptical second-harmonic Tyndall scattering effect. The effect was observed in Si nanohelices, an example of a high-refractive-index dielectric nanomaterial. For three wavelengths of illumination, we observe a clear difference in the second-harmonic scattered light that depends on the chirality of the nanohelices and the handedness of circularly polarized light. Importantly, we provide a theoretical analysis that explains the origin of the effect and its direction dependence, resulting from different specific contributions of "electric dipole-magnetic dipole" and "electric dipole-electric quadrupole" coupling tensors. Using numerical simulations, we narrow down the number of such terms to 8 in forward scattering and to a single one in right-angled scattering. For chiral scatterers such as high-refractive-index dielectric nanoparticles, our findings expand the Tyndall scattering regime to nonlinear optics. Moreover, our theory can be broadened and adapted to further classes where such scattering has already been observed or is yet to be observed.

Chirality, an intrinsic property of certain entities in the universe, is characterized by the absence of mirror symmetry. Understanding chirality is crucial as it influences molecular interactions and properties. Circular dichroism (CD), measured using circularly polarized light, is a standard technique for probing chirality, but its sensitivity is often limited. Here, we explore extrinsic chirality (i.e. a property arising from asymmetric achiral materials when observed from out of normal incidence directions), using photo-acoustic spectroscopy (PAS). PAS allows direct measurement of local absorption, by monitoring the heat produced and transferred to the surrounding air, regardless the transmitted, reflected and scattered light that flows away from the sample. In conventional techniques, the CD is usually measured by taking into account only the extinction as transmitted (or reflected) light. In this study, we introduce a new PAS setup that employs an oblique-incidence laser to study extrinsic chirality in silver-coated self-assembled metasurfaces. Our experimental results reveal intriguing CD trends dependent on the angle of incidence and wavelength, indicative of extrinsic chirality. This study expands the application of PAS, enabling simultaneous analysis of multiple wavelengths and providing valuable insights into chiral metasurfaces.

Achieving a strong and robust chiral response in plasmonic metasurfaces is among the key goals of current nanophotonic research. In this work, we theoretically show that the circular dichroism (CD) of a metal metasurface can be maximized by exploiting the concept of a bound state in a continuum (BIC) with symmetry breaking. We consider a gold metasurface with a deformation of circular holes into oval holes. The chiral response at small values of the angle of incidence is dominated by a quasi-BIC, with nearly maximal values of the absorption CD that are almost independent of the deformation. A strong CD in emission is also demonstrated. Symmetry analysis and mode profiles show that the extrinsically chiral response does indeed follow from a symmetry-broken BIC and is associated with a strong enhancement of the local electrical field. The concept of a plasmonic BIC with symmetry breaking provides a robust pathway to increase the chiral response in metal metasurfaces and opens research opportunities in chiral plasmonics that combine narrow resonances with local field enhancement.

Sensitive and reliable characterization of chirality in nanostructures and molecules is of great importance in multidisciplinary research combining physics, chemistry and nanotechnology, with potential applications in pharmaceutical and agrochemical industry. Chirality is connected to circular dichroism (CD) - the absorption difference when the chiral medium is excited with circular polarizations of opposite handedness. Hence, measuring chirality by direct absorption measurements is of great interest in nanophotonics and plasmonics community, where the nanostructured media can enhance chiro-optical effects. Here we present a recently constructed photo-acoustic spectroscopy (PAS) set-up, which offers many degrees of freedom in characterization. We use a laser which is widely tuneable in the near-infrared (680-1080 nm) and visible (340-540 nm) ranges. The laser output is modulated with a mechanical chopper, where its frequency defines the penetration depth of the thermal signal. The input polarization is controlled by a linear polarizer and a quarter-wave plate, and the laser can be focused before impinging on the sample in the tightly closed photo-acoustic cell. The cell is placed on translational and rotational stages, which allows for the spatial mapping and extrinsic chirality measurements. Finally, a sensitive microphone measures the pressure changes in the cell, enabling scattering-free measurement of absorption and CD.

Chirality, the lack of mirror symmetry, can be mimicked in nanophotonics and plasmonics by breaking the symmetry in light-nanostructure interaction. Here we report on versatile use of nanosphere lithography for the fabrication of low-cost metasurfaces, which exhibit broadband handedness- and angle-dependent extinction in the near-infrared range, thus offering extrinsic chiro-optical behavior. We measure wavelength and angle dependence of the extinction for four samples. Two samples are made of polystyrene nanospheres asymmetrically covered by silver and gold in one case and silver only in the other case, with a nanohole array at the bottom. The other two samples are nanohole arrays, obtained after the nanosphere removal from the first two samples. Rich extrinsic chiral features are governed by different chiro-optical mechanisms in the three-dimensional plasmonic semi-shells and planar nanohole arrays. We also measure Stokes parameters in the same wavelength and incidence angle range and show that the transmitted fields follow the extrinsic chirality features of the extinction dissymmetry. We further study the influences of the nanostructured shapes and in-plane orientations on the intrinsic vs extrinsic chirality. The nanoholes are modelled as oval shapes in metal, showing good agreement with the experiments. We thus confirm that nanosphere lithography can provide different geometries for chiral light manipulation at the nanoscale, with the possibility to extend functionalities with optimized oval shapes and combination of constituent metals.