New Horizons in Near-Zero Refractive Index Photonics and Hyperbolic Metamaterials

Plasmonic nanoarchitectured systems for biomedical application

In this paper we discuss the latest developments in colloidal plasmonics, a field with over a century of history, applied to the biomedical sector. Emphasis is placed on the nanoarchitectonic nature of plasmonic systems that can be used for sensing, drug delivery and manipulation of biomolecules. For instance, quantum effects linked to plasmonic phenomena are being used to enhance monitoring of chiral particles and their interaction with light, which is essential for the pharmaceutical industry in reaching the required enantiopurity in some drugs. In diagnostics, radiofrequency waves can excite surface plasmon resonance through amplified photoacoustic effects, thus permitting thermo-acoustic imaging. An example of enhanced therapy was introduced in carefully designed nanoarchitectures where a multi-branched gold nanooctopus was surrounded by a mesoporous polydopamine and loaded with ribonucleoproteins for the target delivery into tumor cells. Moreover, the longstanding challenge of heating due to Ohmic losses, which has hindered the use of plasmonic tweezers for manipulating biologically relevant analytes, is now being exploited for enhanced trapping, manipulation, and transport of cells and other biological particles. The combination of magnetic materials and plasmonic colloids in the realms of magnetoplasmonics can also be explored in sensing and enhanced drug delivery, which further exemplifies the versatility of nanoarchitectonics.

Nanophotonic Zero-Index-Material-Enabled Optical Coherent Interferometry with High Signal-to-Noise Ratio

Optical interferometry enables distance measurement with record-high precision. However, the conventional interference intensity shows fast spatial variations, limiting photodetection to a single spot. The light intensity at this spot is affected by various noises, restricting the signal-to-noise ratio (SNR) of a coherent system. Here, we generate uniform interference patterns based on zero-index metawaveguides, enabling the photodetection of spatially extended intensity through multiple-pixel measurements of a charge-coupled device. Averaging the intensities measured across multiple pixels cancels uncorrelated noise, significantly improving the SNR and allowing the detection of weakly reflected optical power. Experiments show that nanoscale displacements down to 26 nm (λ0/59) can be converted into high-contrast intensity changes over a macroscopic area, leading to an SNR 10+ times higher (11.68 dB) than that of conventional single-spot photodetection. Our nanophotonic zero-index platform can be implemented in any coherent system, possibly leading to a transformative impact in precise measurement of the distance, profile, and spectrum.

Review on the Scientific and Technological Breakthroughs in Thermal Emission Engineering

The emission of thermal radiation is a physical process of fundamental and technological interest. From different approaches, thermal radiation can be regarded as one of the basic mechanisms of heat transfer, as a fundamental quantum phenomenon of photon production, or as the propagation of electromagnetic waves. However, unlike light emanating from conventional photonic sources, such as lasers or antennas, thermal radiation is characterized for being broadband, omnidirectional, and unpolarized. Due to these features, ultimately tied to its inherently incoherent nature, taming thermal radiation constitutes a challenging issue. Latest advances in the field of nanophotonics have led to a whole set of artificial platforms, ranging from spatially structured materials and, much more recently, to time-modulated media, offering promising avenues for enhancing the control and manipulation of electromagnetic waves, from far- to near-field regimes. Given the ongoing parallelism between the fields of nanophotonics and thermal emission, these recent developments have been harnessed to deal with radiative thermal processes, thereby forming the current basis of thermal emission engineering. In this review, we survey some of the main breakthroughs carried out in this burgeoning research field, from fundamental aspects to theoretical limits, the emergence of effects and phenomena, practical applications, challenges, and future prospects.

Magnetically tunable Brewster angle in uniaxial magneto-optical metamaterials for advanced integration of high-resolution sensing devices

In this Letter, we introduce a concept to produce high-resolution, highly integrable biosensing devices. Our idea exploits the highly absorbing modes in multilayered metamaterials to maximize the transverse magneto-optical Kerr effect (TMOKE). Results are discussed in the context of dielectric uniaxial (ε eff,∥ ε eff,⊥>0) and hyperbolic metamaterial (ε eff,∥ ε eff,⊥<0) regimes. For applications in gas sensing, we obtained sensitivities of S = 46.02 deg/RIU and S = 73.91 deg/RIU when considering the system working in the uniaxial and hyperbolic regimes, respectively, with figures of merit (resolution) in the order of 310 or higher. On the contrary, when considering the system for biosensing applications (incidence from an aqueous medium), we observed that the proposed mechanism can only be successfully used in the uniaxial regime, where a sensitivity of 56.87 deg/RIU was obtained.

Magnetochiroptical nanocavities in hyperbolic metamaterials enable sensing down to the few-molecule level

In this work, we combine the concepts of magnetic circular dichroism, nanocavities, and magneto-optical hyperbolic metamaterials (MO-HMMs) to demonstrate an approach for sensing down to a few molecules. Our proposal comprises a multilayer MO-HMM with a square, two-dimensional arrangement of nanocavities. The magnetization of the system is considered in polar configuration, i.e., in the plane of polarization and perpendicular to the plane of the multilayer structure. This allows for magneto-optical chirality to be induced through the polar magneto-optical Kerr effect, which is exhibited by reflected light from the nanostructure. Numerical analyses under the magnetization saturation condition indicate that magnetic circular dichroism peaks can be used instead of reflectance dips to monitor refractive index changes in the analyte region. Significantly, we obtained a relatively high sensitivity value of S = 40 nm/RIU for the case where refractive index changes are limited to the volume inside nanocavities, i.e., in the limit of a few molecules (or ultralow concentrations), while a very large sensitivity of S = 532 nm/RIU is calculated for the analyte region distributed along the entire superstrate layer.