Silicon metaoptics for the compact generation of perfect vector beams in the telecom infrared.

Perfect vortices have attracted considerable attention as orbital angular momentum (OAM) beams with customizable ring-like intensity distribution. More recently, the non-separable combination of perfect vortices with opposite OAMs and spins, yielding so-called perfect vector beams, has further expanded their applications in the fields of optical manipulation and imaging, high-resolution lithography, and telecommunications. Exploiting the combined manipulation of dynamic and geometric phases using silicon anisotropic metaunits, here we present the design, fabrication, and characterization of novel, to the best of our knowledge, dielectric metaoptics for the compact generation of perfect vector beams in the telecom infrared using a single metasurface. These devices pave the way to integrated optical architectures with applications in information and communication technologies in both the classical and quantum regimes.

Toward an integrated device for spatiotemporal superposition of free-electron lasers and laser pulses.

Free-electron lasers (FELs) currently represent a step forward on time-resolved investigations on any phase of matter through pump-probe methods involving FELs and laser beams. That class of experiments requires an accurate spatial and temporal superposition of pump and probe beams on the sample, which at present is still a critical procedure. More efficient approaches are demanded to quickly achieve the superposition and synchronization of the beams. Here, we present what we believe is a novel technique based on an integrated device allowing the simultaneous characterization and the fast spatial and temporal overlapping of the beams, reducing the alignment procedure from hours to minutes.

Half-wet nanomechanical sensors for cellular dynamics investigations.

Testing devices based on cell tracking are particularly interesting as diagnostic tools in medicine for antibiotics susceptibility testing and in vitro chemotherapeutic screening. In this framework, the application of nanomechanical sensors has attracted much attention, although some crucial aspects such as the effects of the viscous damping, when operating in physiological conditions environment, still need to be properly solved. To address this problem, we have designed and fabricated a nanomechanical force sensor that operates at the interface between liquid and air. Our sensor consists of a silicon chip including a 500 µm wide Si3N4 suspended membrane where three rectangular silicon nitride cantilevers are defined by a lithographically etched gap. The cantilevers can be operated in air, fully immersed in a liquid environment and in half wetting condition, with one side in contact with the solution and the opposite one in air. The formation of a water meniscus in the gap prevents the leakage of medium to the opposite side, which remained dry and is used to reflect a laser to measure the cantilever deflection. This configuration enables to keep the cells in physiological environment while operating the sensor in dry conditions. The performance of the sensor has been applied to monitor the motion and measures the forces developed by migrating breast cancer cell. The functionalization of one side of the cantilever and the use of a purposely designed chamber of measurements enable the confinement of the cell only on one side of the cantilever. Our data demonstrate that this approach can distinguish the adhesion and contraction forces developed by different cell lines and may represents valuable tool for a fast and quantitative in-vitro screening of new chemotherapeutic drugs targeting cancer cell adhesion and motility.

Fabrication of 3D Oriented MOF Micropatterns with Anisotropic Fluorescent Properties.

Micropatterning crystalline materials with oriented pores is necessary for the fabrication of devices with anisotropic properties. Crystalline and porous metal-organic frameworks (MOFs) are ideal materials as their chemical and structural mutability enables precise tuning of functional properties for applications ranging from microelectronics to photonics. Herein, a patternable oriented MOF film is designed: by using a photomask under X-ray exposure, the MOF film decomposes in the irradiated areas, remaining intact in the unexposed regions. The MOF film acts simultaneously as a resist and as functional porous material. While the heteroepitaxial growth from aligned Cu(OH)2 nanobelts is used to deposit oriented MOF films, the sensitivity to radiation is achieved by integrating a brominated dicarboxylate ligand (Br2 BDC) into a copper-based MOF Cu2 L2 DABCO (DABCO = 1,4-diazabicyclo[2.2.2]octane; L = BDC/Br2 BDC). The lithographed samples act as diffraction gratings upon irradiation with a laser, thus confirming the quality of the extended MOF micropattern. Furthermore, the oriented MOF patterns are functionalized with fluorescent dyes. As a result, by rotating the polarization angle of the laser excitation, the alignment of the dye in the MOF is demonstrated. By controlling the functional response to light, this MOF patterning protocol can be used for the microfabrication of optical components for photonic devices.

Patterned Carboxymethyl-Dextran Functionalized Surfaces Using Organic Mixed Monolayers for Biosensing Applications.

The deposition of biomolecules on biosensing surface platforms plays a key role in achieving the required sensitivity and selectivity for biomolecular interactions analysis. Controlling the interaction between the surface and biomolecules is increasingly becoming a crucial design tool to modulate the surface properties needed to improve the performance of the assay and the detection outcome. Carboxymethyl-dextran (CMD) coating can be exploited to promote chemical grafting of proteins, providing a hydrophilic, bioinert, nonfouling surface and a high surface density of immobilized proteins. In the present work, we developed and optimized a technique to produce a cost-effective CMD-based patterned surface for the immobilization of biomolecules to be used on standard protocols optimization. They consist of silicon or glass substrates with patterned bioactive areas able to efficiently confine the sampling solution by simply exploiting hydrophilic/hydrophobic patterning of the surface. The fabrication process involves the use of low-cost instruments and techniques, compatible with large scale production. The devices were validated through a chemiluminescence assay we recently developed for the analysis of binding of DNA nanoassemblies modified with an affinity binder to target proteins immobilized on the bioactive areas. Through this assay we were able to characterize the chemical reactivity of two target proteins toward a dextran matrix on patterned surfaces and to compare it with model CMD-based surface plasmon resonance (SPR) surfaces. We found a high reproducibility and selectivity in molecular recognition, consistent with results obtained on SPR sensor surfaces. The suggested approach is straightforward, cheap, and provides the means to assess patterned functionalized surfaces for bioanalytical platforms.

Unraveling the timescale of the structural photo-response within oriented metal-organic framework films.

Fundamental knowledge on the intrinsic timescale of structural transformations in photo-switchable metal-organic framework films is crucial to tune their switching performance and to facilitate their applicability as stimuli-responsive materials. In this work, for the first time, an integrated approach to study and quantify the temporal evolution of structural transformations is demonstrated on an epitaxially oriented DMOF-1-on-MOF film system comprising azobenzene in the DMOF-1 pores (DMOF-1/AB). We employed time-resolved Grazing Incidence Wide-Angle X-Ray Scattering measurements to track the structural response of the DMOF-1/AB film upon altering the length of the azobenzene molecule by photo-isomerization (trans-to-cis, 343 nm; cis-to-trans, 450 nm). Within seconds, the DMOF-1/AB response occurred fully reversible and over several switching cycles by cooperative photo-switching of the oriented DMOF-1/AB crystallites as confirmed further by infrared measurements. Our work thereby suggests a new avenue to elucidate the timescales and photo-switching characteristics in structurally responsive MOF film systems.

Tunable cryogenic terahertz cavity for strong light-matter coupling in complex materials.

We report here the realization and commissioning of an experiment dedicated to the study of the optical properties of light-matter hybrids constituted of crystalline samples embedded in an optical cavity. The experimental assembly developed offers the unique opportunity to study the weak and strong coupling regimes between a tunable optical cavity in cryogenic environment and low energy degrees of freedom, such as phonons, magnons, or charge fluctuations. We describe here the setup developed that allows for the positioning of crystalline samples in an optical cavity of different quality factors, the tuning of the cavity length at cryogenic temperatures, and its optical characterization with a broadband time domain THz spectrometer (0.2-6 THz). We demonstrate the versatility of the setup by studying the vibrational strong coupling in CuGeO3 single crystal at cryogenic temperatures.

Multi-layered ZIF-coated cells for the release of bioactive molecules in hostile environments.

Metal-organic framework (MOF) coatings on cells enhance viability in cytotoxic environments. Here, we show how protective multi-layered MOF bio-composite shells on a model cell system (yeast) enhance the proliferation of living cells exposed to hostile protease-rich environments via the dissolution of the shells and release of a protease inhibitor (antitrypsin).

A novel free-electron laser single-pulse Wollaston polarimeter for magneto-dynamical studies.

Here, we report on the conceptual design, the hardware realization, and the first experimental results of a novel and compact x-ray polarimeter capable of a single-pulse linear polarization angle detection in the extreme ultraviolet photon energy range. The polarimeter is tested by performing time resolved pump-probe experiments on a Ni80Fe20 Permalloy film at the M2,3 Ni edge at an externally seeded free-electron laser source. Comparison with similar experiments reported in the literature shows the advantages of our approach also in view of future experiments.