Valerio Pruneri

The growing demand for monitoring and detecting biochemical changes is driving the development of scalable, easy-to-fabricate, and low-power consuming sensor technologies. In particular, chemiresistors are simple and cost-effective platforms that transduce chemical interactions into measurable electrical signals. Due to the large high surface-to-volume ratio, ultrathin metal films (UTMFs) have the potential for highly sensitive transducing materials. In this study, we investigate the suitability of gold (Au) UTMFs as chemiresistive transducing material by quantifying how film thickness influences their resistive response. As a prototypical detection target, we use self-assembled monolayers (SAMs) that can be easily functionalized on the Au UTMF surface. Real-time resistance measurements during SAM formation demonstrate that the thinner the Au UTMFs, the higher the sensitivity and the faster the response. In addition, we present a proof-of-concept biosensor using SH-PEG-Biotin SAMs for the detection of streptavidin, comparing the responses between shorter and longer PEG chains. The results show that shorter PEG chains forming SAMs provide greater sensitivity and a lower limit of detection. These results highlight the potential use of Au UTMF-based chemiresistors with SAMs as scalable and tunable biosensing platforms, where sensitivity and performance can be tailored via surface molecular engineering.

We present the development of transparent, color-neutral, antimicrobial surfaces tailored for integration in touchscreen display applications. Co-sputtered copper-zinc Ultra-Thin Metal Film is deposited on Gorilla®Glass substrate and subsequently annealed to perform nanostructuring. Cu–Zn mixed material maintains high antimicrobial efficacy inherent of copper while the presence of the zinc acts in dampening the color of pure copper which offers a significantly improved color neutrality. The optimized nanostructured surface exhibits optical transmission exceeding 80% in the visible spectrum and a color difference ΔE under 3 in the CIE 1976 Lab* color space, satisfying stringent display industry standards for visual clarity and neutrality. Additionally, the nanostructured surface possesses electrical insulation to support capacitive touch functionality. Antimicrobial performance was validated through biological analysis on both as-deposited and thermally annealed samples, demonstrating high bactericidal efficacy that meets the U.S. Environmental Protection Agency requirements. These findings place Cu–Zn based device as a scalable and effective solution for next-generation hygienic interactive display technologies thanks to the lithography-free fabrication process.

Touch-enabled technologies, from smartphones to public kiosks, are ubiquitous, yet frequent use turns their surfaces into reservoirs for microbial contamination. Routine alcohol-based cleaning can be impractical on high-touch optical surfaces due to damage risk and usability concerns. Here, we present a scalable approach to transparent, mechanically robust glass surfaces by embedding materials with ad hoc functionality into surface glass nanoholes. We demonstrate the concept with copper nanodisks: copper is an established antimicrobial agent, but its wear susceptibility pose challenges for use on transparent displays. Our design shields the functional material from lateral wear while allowing ion diffusion for antimicrobial efficacy. Fabrication uses only wafer-compatible, lithography-free steps: thermal dewetting of a thin silver film to create a nanosized mask; inverting it to a polymer nanoholes mask by etching the silver nanoparticles; wet etching of the glass to form nanoholes; selective copper deposition inside these holes; and liftoff of excess material. The resulting surfaces exhibit mean transmission of 80%–85% in the 380–750 nm range with haze <1% and minimal color shift, compared to uncoated glass. Antimicrobial efficacy, assessed against Escherichia coli OP50 under a modified U.S. EPA protocol, shows ≈99% bacterial reduction within one hour. Abrasion tests with a crockmeter simulating finger swipes confirm that the embedded copper remains intact, with no measurable change in optical performance. This embedded design provides a scalable route to integrate antimicrobial functionality into high-touch transparent systems while preserving optical clarity and wear resistance, with potential relevance for medical, consumer, and transportation interfaces.

We experimentally demonstrate undetected photon phase sensing on a silicon photonic chip. We use a novel design, implementing an innovative integrated SU(1,1) interferometer based on transverse waveguide modes, that leverages intermodal spontaneous four-wave mixing to generate highly non-degenerate idler–signal photons. In our experiment, we retrieve the phase applied to the signal photons at wavelength 1972 nm by detecting only the correlated idler photons at 1291 nm, demonstrating the first on-chip phase sensing based on undetected photons. This result paves the way for novel generations of quantum refractometric sensors.

Entangled photon sources (EPSs) are pivotal in advancing quantum communication, computing, and sensing. The demand for deploying efficient, robust EPSs in the field, characterized by exceptional (phase) stability, has become increasingly apparent. This work introduces a polarization-entangled photon source, leveraging type-0 spontaneous parametric downconversion and constructed using commercial bulk optomechanical components. Our system is versatile, enabling the generation of N00N states for sensing applications or Bell states for quantum key distribution protocols. We attained a maximal Bell inequality violation, with the average entanglement visibility exceeding 99%. The potential for further performance enhancements is also explored.

Integrated quantum sources are proving to be the most effective technology of sources for scalable quantum applications. A platform that satisfies all the requirements has not prevailed yet. In this framework, we report, to the best of our knowledge, the first demonstration of a photon pair source in a silicon core fiber. The fiber, only 58 mm long, works at room temperature and shows an intrinsic brightness of 570 kHz/nm/mW2 and a coincidence-to-accidental ratio of 133 ± 2 at around 1.55 μm wavelength. The low propagation losses of the platform, ∼0.3 dB/cm in our source, pave the way for effective fiber-based quantum sources in the telecom band. A comparison with state-of-the-art further confirms the potential of this platform for future applications, especially in the field of quantum communication.

In this paper, we demonstrate a novel optical characterization method for ultrathin semitransparent and absorbing materials through multispectral intensity and phase imaging. The method is based on a lateral-shearing interferometric microscopy (LIM) technique, where phase-shifting allows extraction of both the intensity and the phase of transmitted optical fields. To demonstrate the performance in characterizing semitransparent thin films, we fabricated and measured cupric oxide (CuO) seeded gold ultrathin metal films (UTMFs) with mass-equivalent thicknesses from 2 to 27 nm on fused silica substrates. The optical properties were modeled using multilayer thin film interference and a parametric model of their complex refractive indices. The UTMF samples were imaged in the spectral range from 475 to 750 nm using the proposed LIM technique, and the model parameters were fitted to the measured data in order to determine the respective complex refractive indices for varying thicknesses. Overall, by using the combined intensity and phase not only for imaging and quality control but also for determining the material properties, such as complex refractive indices, this technique demonstrates a high potential for the characterization of the optical properties, of (semi-) transparent thin films.

Traditional multilayer antireflection (AR) surfaces are of significant importance for numerous applications, such as laser optics, camera lenses, and eyeglasses. Recently, technological advances in the fabrication of biomimetic AR surfaces capable of delivering broadband omnidirectional high transparency combined with self-cleaning properties have opened an alternative route toward realization of multifunctional surfaces which would be beneficial for touchscreen displays or solar harvesting devices. However, achieving the desired surface properties often requires sophisticated lithography fabrication methods consisting of multiple steps. In the present work, we show the design and implementation of mechanically robust AR surfaces fabricated by a lithography-free process using thermally dewetted silver as an etching mask. Both-sided nanohole (NH) surfaces exhibit transmittance above 99% in the visible or the near-infrared ranges combined with improved angular response at an angle of incidence of up to θ_i = 60°. Additionally, the NHs demonstrate excellent mechanical resilience against repeated abrasion with cheesecloth due to favorable redistribution of the shearing mechanical forces, making them a viable option for touchscreen display applications.

Metallic copper is a potent antimicrobial agent with high efficacy against a range of microorganisms. Whilst it is commonplace for objects such as door handles and hospital bedrails to be made of or to be coated with copper, other high-touch surfaces such as those of screens and monitors would lose their optical transparency. Herein, we report the design of a transparent antimicrobial nanostructured copper surface obtained by dewetting ultrathin metal copper films on glass. Antimicrobial effectiveness of >99.9 % was obtained within 2 h against Staphylococcus aureus following the US Environmental Protection Agency Test method. Moreover, the proposed surfaces show an average transmittance between 70–80% with little color in the visible range. Additionally, they maintain optical and antimicrobial properties after abrasion and chemical exposure tests designed to replicate physical wear and repeated exposure to biocidal cleaning materials. With the demonstrated surfaces’ antimicrobial, colorless, and durability properties, they have potential in applications such as touch-enabled public or personal displays once higher transparency is achieved.

Compressing light into nanocavities substantially enhances light–matter interactions, which has been a major driver for nanostructured materials research. However, extreme confinement generally comes at the cost of absorption and low resonator quality factors. Here we suggest an alternative optical multimodal confinement mechanism, unlocking the potential of hyperbolic phonon polaritons in isotopically pure hexagonal boron nitride. We produce deep-subwavelength cavities and demonstrate several orders of magnitude improvement in confinement, with estimated Purcell factors exceeding 10⁸ and quality factors in the 50–480 range, values approaching the intrinsic quality factor of hexagonal boron nitride polaritons. Intriguingly, the quality factors we obtain exceed the maximum predicted by impedance-mismatch considerations, indicating that confinement is boosted by higher-order modes. We expect that our multimodal approach to nanoscale polariton manipulation will have far-reaching implications for ultrastrong light–matter interactions, mid-infrared nonlinear optics and nanoscale sensors.