Magnetic control of particle trapping in a hybrid plasmonic nanopore

in Applied Physics Letters (2021), 118

Plasmonic nanopores are extensively investigated as single molecules detectors. The main limitations in plasmonic nanopore technology are the too fast translocation velocity of the molecule through the ... [more ▼]

Plasmonic nanopores are extensively investigated as single molecules detectors. The main limitations in plasmonic nanopore technology are the too fast translocation velocity of the molecule through the pore and the consequent very short analysis times, as well as the possible instabilities due to local heating. An interesting approach to enable longer acquisition times is represented by the ability to stably trap the nanoparticles used to tag molecules close to the nanopore. Here, we theoretically investigate the performance of a magneto-plasmonic nanopore prepared with a thin layer of cobalt sandwiched between two gold layers. A nanopore is then coupled with a bifunctional (magnetic and plasmonic) core–shell nanoparticle made of magnetite (core) covered with a thin layer of gold (shell). By setting the magnetic configuration of the cobalt layer around the pore by an external magnetic field, it is possible to generate a nanoscale magnetic tweezer to trap the nanoparticle at a specific point. Considering a ∼10 nm diameter magnetite nanoparticle, we calculate a trapping force up to 28 pN, an order of magnitude above the force that can be obtained with standard optical or plasmonic trapping approaches. Moreover, the magnetic force pulls the nanoparticle in close contact with the plasmonic nanopore's wall, thus enabling the formation of a nanocavity enclosing a sub-10 nm3 confined electromagnetic field with an average field intensity enhancement up to 230 at near-infrared wavelengths. The presented hybrid magneto-plasmonic system points toward a strategy to improve nanopore-based biosensors for single-molecule detection and potentially for the analysis of various biomolecules. [less ▲]

Ultrafast opto-acoustic modulation of light reflectance in metal-insulator-metal epsilon-near-zero nanocavities

in Proceedings of SPIE: The International Society for Optical Engineering (2021), 11769

We report on ultrafast opto-acoustic modulation of light reflectance in artificial epsilon-near-zero metamaterials made of two layers of Ag separated by an Al2O3 layer. By means of non-degenerate two ... [more ▼]

We report on ultrafast opto-acoustic modulation of light reflectance in artificial epsilon-near-zero metamaterials made of two layers of Ag separated by an Al2O3 layer. By means of non-degenerate two color pump-probe experiments we demonstrate an optically induced acoustic modulation of the reflectance up to 20% via generation of acoustic waves inside the cavity upon mechanical expansion of the metal due to hot electron-phonon coupling nonlinearity in the Ag layers. The presented architecture opens the pathway towards novel routes to exploit light-matter interactions for opto-acoustic modulation at GHz frequencies. Moreover, our system can be designed to work in transmission geometry and is very versatile in terms of shifting the presented properties along a broad range of wavelengths, from UV to mid-IR. Our approach, beyond light-driven information processing, might impact also opto-mechanics, light-driven phonon induced up conversion mechanisms, non-linear optical and acoustic properties of materials, energy harvesting, and heat-assisted ultrafast magneto-optical recording. [less ▲]

Recent advances on plasmonic nanocavities for single-molecule spectroscopy

in Nanoscale Advances (2021), 3

Plasmonic nanocavities are able to engineer and confine electromagnetic fields into subwavelength volumes. In the past decade, they have enabled a large set of applications, in particular for sensing ... [more ▼]

Plasmonic nanocavities are able to engineer and confine electromagnetic fields into subwavelength volumes. In the past decade, they have enabled a large set of applications, in particular for sensing, optical trapping, as well as the investigation of physical and chemical phenomena at a few or single-molecule levels. This extreme sensitivity is possible thanks to the highly confined local field intensity enhancement, which depends on the geometry of the plasmonic nanocavities. Indeed, properly designed structures providing engineered local optical fields lead to enhanced optical sensing based on different phenomena like surface enhanced Raman scattering, fluorescence, and Förster Resonant Energy Transfer. In this mini-review, we illustrate the most recent results on plasmonic nanocavities, with specific emphasis on the detection of single molecules. [less ▲]

Hyperbolic dispersion metasurfaces for molecular biosensing

in Nanophotonics (2021), 10(1), 295314

Sensor technology has become increasingly crucial in medical research and clinical diagnostics to directly detect small numbers of low-molecular-weight biomolecules relevant for lethal diseases. In recent ... [more ▼]

Sensor technology has become increasingly crucial in medical research and clinical diagnostics to directly detect small numbers of low-molecular-weight biomolecules relevant for lethal diseases. In recent years, various technologies have been developed, a number of them becoming core label-free technologies for detection of cancer biomarkers and viruses. However, to radically improve early disease diagnostics, tracking of disease progression and evaluation of treatments, today’s biosensing techniques still require a radical innovation to deliver high sensitivity, specificity, diffusion-limited transport, and accuracy for both nucleic acids and proteins. In this review, we discuss both scientific and technological aspects of hyperbolic dispersion metasurfaces for molecular biosensing. Optical metasurfaces have offered the tantalizing opportunity to engineer wavefronts while its intrinsic nanoscale patterns promote tremendous molecular interactions and selective binding. Hyperbolic dispersion metasurfaces support high-k modes that proved to be extremely sensitive to minute concentrations of ultralow-molecular-weight proteins and nucleic acids. [less ▲]

Magnetophotonics for sensing and magnetometry toward industrial applications

in Journal of Applied Physics (2021), 130

Magnetic nanostructures sustaining different types of optical modes have been used for magnetometry and label-free ultrasensitive refractive index probing, where the main challenge is the realization of ... [more ▼]

Magnetic nanostructures sustaining different types of optical modes have been used for magnetometry and label-free ultrasensitive refractive index probing, where the main challenge is the realization of compact devices that are able to transfer this technology from research laboratories to smart industry. This Perspective discusses the state-of-the-art and emerging trends in realizing innovative sensors containing new architectures and materials exploiting the unique ability to actively manipulate their optical properties using an externally applied magnetic field. In addition to the well-established use of propagating and localized plasmonic fields, in the so-called magnetoplasmonics, we identified a new potential of the all-dielectric platforms for sensing to overcome losses inherent to metallic components. In describing recent advances, emphasis is placed on several feasible industrial applications, trying to give our vision on the future of this promising field of research merging optics, magnetism, and nanotechnology. [less ▲]

Speeding up nanoscience and nanotechnology with ultrafast plasmonics

in Nano Letters (2020)

Surface plasmons are collective oscillations of free electrons at the interface between a conducting material and the dielectric environment. These excitations support the formation of strongly enhanced ... [more ▼]

Surface plasmons are collective oscillations of free electrons at the interface between a conducting material and the dielectric environment. These excitations support the formation of strongly enhanced and confined electromagnetic fields. As well, they display fast dynamics lasting tens of femtoseconds and can lead to a strong nonlinear optical response at the nanoscale. Thus, they represent the perfect tool to drive and control fast optical processes, such as ultrafast optical switching, single photon emission, as well as strong coupling interactions to explore and tailor photochemical reactions. In this Virtual Issue, we gather several important papers published in Nano Letters in the past decade reporting studies on the ultrafast dynamics of surface plasmons. [less ▲]

Machine learning in nanoscience: big data at small scales

in Nano Letters (2020), 20(1), 2-10

Recent advances in machine learning (ML) offer new tools to extract new insights from large data sets and to acquire small data sets more effectively. Researchers in nanoscience are experimenting with ... [more ▼]

Recent advances in machine learning (ML) offer new tools to extract new insights from large data sets and to acquire small data sets more effectively. Researchers in nanoscience are experimenting with these tools to tackle challenges in many fields. In addition to ML’s advancement of nanoscience, nanoscience provides the foundation for neuromorphic computing hardware to expand the implementation of ML algorithms. In this mini-review, which is not able to be comprehensive, we highlight some recent efforts to connect the ML and nanoscience communities focusing on three types of interaction: (1) using ML to analyze and extract new information from large nanoscience data sets, (2) applying ML to accelerate materials discovery, including the use of active learning to guide experimental design, and (3) the nanoscience of memristive devices to realize hardware tailored for ML. We conclude with a discussion of challenges and opportunities for future interactions between nanoscience and ML researchers. [less ▲]

Plasmon Hybridization in Compressible Metal-Insulator-Metal Nano-Cavities: an Optical Approach for Sensing Deep Sub-Wavelength Deformation

in Advanced Optical Materials (2020), 8(18), 2000609

We present a pressure-induced deformation-sensitive device based on 2D matrices of plasmonic gold nanodisks coupled to a metal thin layer through a compressible dielectric spacer, namely a deformable ... [more ▼]

We present a pressure-induced deformation-sensitive device based on 2D matrices of plasmonic gold nanodisks coupled to a metal thin layer through a compressible dielectric spacer, namely a deformable metal-insulator-metal (MIM) nanocavity, to report deep sub-wavelength size variations (< λ/200). The system is characterized by two hybrid branches, which are resonant in the visible/near infrared spectral region. The fundamental mode, owing to the near-field interaction between the plasmonic nanostructures and the metal film, exhibits a remarkable sensitivity to the gap size, exceeding that of a planar “macroscopic” optical cavity and extending its operational domain to the sub-wavelength range, where excellent opportunities towards truly multiscale MIMs-based pressure sensors can be envisioned. Concurrently, its intrinsic plasmonic nature synergistically combines into a single platform multi-purpose functionalities, such as ultrasensitive detection, remote temperature readout etc., with practical perspectives in ultra-compact inspection tools for structural and functional information at the nanoscale. [less ▲]

Two-state switchable plasmonic tweezers for dynamic manipulation of nano-objects

in Nanoscale (2020), 12

In this work, we present a plasmonic platform capable of trapping nano-objects in two different spatial configurations. The switch between the two trapping states, localized on the tip and on the outer ... [more ▼]

In this work, we present a plasmonic platform capable of trapping nano-objects in two different spatial configurations. The switch between the two trapping states, localized on the tip and on the outer wall of a vertical gold nanochannel, can be activated by varying the focusing position of the excitation laser along the main axis of the nanotube. We show that the switching of the trapping site is induced by changes in the distribution of the electromagnetic field and of the trapping force. The “inner” and “outer” trapping states are characterized by a static and a dynamic behavior respectively, and their stiffness is measured by analyzing the positions of the trapped specimens as a function of time. In addition, we demonstrate that the stiffness of the static state is high enough to trap particles with diameter as small as 40 nm. These results show a simple, controllable way to generate a switchable two-state trapping regime, which could be used as a model for the study of dynamic trapping or as a mechanism for the development of nanofluidic devices. [less ▲]

Intracellular recording of human cardiac action potentials on market-available multielectrode array platforms

in Frontiers in Bioengineering and Biotechnology (2020), 8

High quality attenuated intracellular action potentials from large cell networks can be recorded on multi-electrode arrays by means of 3D vertical nanopillars using electrical pulses. However,most of the ... [more ▼]

High quality attenuated intracellular action potentials from large cell networks can be recorded on multi-electrode arrays by means of 3D vertical nanopillars using electrical pulses. However,most of the techniques require complex 3D nanostructures that prevent the straightforward translation into marketable products and the wide adoption in the scientific community. Moreover, 3D nanostructures are often delicate objects that cannot sustain several harsh use/cleaning cycles. On the contrary, laser optoacoustic poration allows the recording of action potentials on planar nanoporous electrodes made of noble metals. However, these constraints of the electrode material and morphology may also hinder the full exploitation of this methodology. Here, we show that optoacoustic poration is also very effective for porating cells on a large family of MEA electrode configurations, including robust electrodes made of nanoporous titanium nitride or disordered fractal-like gold nanostructures. This enables the recording of high quality cardiac action potentials in combination with optoacoustic poration, providing thus attenuated intracellular recordings on various already commercial devices used by a significant part of the research and industrial communities. [less ▲]