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Optical biosensors based on surface plasmon resonance (SPR) in metallic thin films are currently standard tools for measuring molecular binding kinetics and affinities – an important task for biophysical studies and pharmaceutical development. Motivated by recent progress in the design and fabrication of metallic nanostructures, such as nanoparticles or nanoholes of various shapes, researchers have been pursuing a new generation of biosensors harnessing tailored plasmonic effects in these engineered nanostructures. Nanoplasmonic devices, while demanding nanofabrication, offer tunability with respect to sensor dimension and physical properties, thereby enabling novel biological interfacing opportunities and extreme miniaturization. Here we provide an integrated overview of refractometric biosensing with nanoplasmonic devices and highlight some recent examples of nanoplasmonic sensors capable of unique functions that are difficult to accomplish with conventional SPR. For example, since the local field strength and spatial distribution can be readily tuned by varying the shape and arrangement of nanostructures, biomolecular interactions can be controlled to occur in regions of high field strength. This may improve signal-to-noise and also enable sensing a small number of molecules. Furthermore, the nanoscale plasmonic sensor elements may, in combination with nanofabrication and materials-selective surface-modifications, make it possible to merge affinity biosensing with nanofluidic liquid handling.

High carrier mobility and tunability in graphene enable fundamental studies for plasmonics and various applications. Despite its versatility, however, single‐layer graphene (SLG) suffers from poor coupling efficiency to electromagnetic waves, presenting a major challenge for photonic applications. Compared with visible or infrared radiation, terahertz (THz) waves exhibit higher absorption in SLG due to Drude‐like intraband transitions, but the wavelength‐to‐SLG size mismatch becomes even more dramatic. Here, we experimentally demonstrate 99% extinction of THz wave transmission when SLG covers the openings of 2‐nm‐wide (≈λ/1 000 000) slits through a metal film. By resonantly coupling THz waves through annular nanogaps, the extremely localized fields lead to near‐perfect extinction and strong absorption in SLG. Atomic‐layer lithography is used to produce these nanometer‐wide, millimeter‐long gaps over an entire 4‐in. wafer. Furthermore, by integrating these devices with an ionic liquid, enhanced intraband absorption in the SLG leads to 80% modulation of THz waves with an operational voltage as low as 1.5 V. [ABSTRACT FROM AUTHOR]

The ability to precisely control the topography, roughness, and chemical properties of metallic nanostructures is crucial for applications in plasmonics, nanofluidics, electronics, and biosensing. Here a simple method to produce embedded nanoplasmonic devices that can generate tunable plasmonic fields on ultraflat surfaces is demonstrated. Using a template-stripping technique, isolated metallic nanodisks and wires are embedded in optical epoxy, which is capped with a thin silica overlayer using atomic layer deposition. The top silica surface is topographically flat and laterally homogeneous, providing a uniform, high-quality biocompatible substrate, while the nanoplasmonic architecture hidden underneath creates a tunable plasmonic landscape for optical imaging and sensing. The localized surface plasmon resonance of gold nanodisks embedded underneath flat silica films is used for real-time kinetic sensing of the formation of a supported lipid bilayer and subsequent receptor-ligand binding. Gold nanodisks can also be embedded in elastomeric materials, which can be peeled off the substrate to create flexible plasmonic membranes that conform to non-planar surfaces. [ABSTRACT FROM AUTHOR]

Nanofabricated metallic tips are at the core of important research in single-molecule imaging, near-field scanning optical microscopy, tip-enhanced Raman spectroscopy, as well as potential commercial applications such as heat-assisted magnetic recording. While challenging to fabricate, much progress has been made towards the reliable production of extremely sharp (10 nm) metallic probes. In this review, the various factors that go into the design of metallic tips, their fabrication, packaging and system integration, characterization, passivation, and eventual use are discussed. Fabrication challenges, implementation issues, optical excitation schemes, and various current and emerging applications are also discussed. For the rapidly emerging fields of plasmonics and nanophotonics, the use of sharp metallic tips has generated significant scientific progress and will play an integral role well into the future. [ABSTRACT FROM AUTHOR]

On page 2812, Sang‐Hyun Oh and co‐workers report using template stripping to create embedded plasmonic nanodisks that can generate tunable plasmonic fields on ultraflat surfaces. The embedded nanodisks are topographically flat and capped with a silica layer to form a laterally homogeneous and biocompatible substrate. The nanoplasmonic architecture hidden underneath creates a tunable plasmonic landscape. Nanostructures can also be embedded in elastomeric materials, which can be peeled off the substrate to create flexible plasmonic membranes that conform to nonplanar surfaces. [ABSTRACT FROM AUTHOR]

We have combinedatomic layer lithography and template stripping to produce a new classof substrates for surface-enhanced infrared absorption (SEIRA) spectroscopy.Our structure consists of a buried and U-shaped metal–insulator–metalwaveguide whose folded vertical arms efficiently couple normally incidentlight. The insulator is formed by atomic layer deposition (ALD) ofAl2O3and precisely defines the gap size. Theburied nanocavities are protected from contamination by a silicontemplate until ready for use and exposed by template stripping ondemand. The exposed nanocavity generates strong infrared resonances,tightly confines infrared radiation into a gap that is as small as3 nm (λ/3300), and creates a dense array of millimeter-longhotspots. After partial removal of the insulators, the gaps are backfilledwith benzenethiol molecules, generating distinct Fano resonances dueto strong coupling with gap plasmons, and a SEIRA enhancement factorof 105is observed for a 3 nm gap. Because of the wafer-scalemanufacturability, single-digit-nanometer control of the gap sizevia ALD, and long-term storage enabled by template stripping, ourburied plasmonic nanocavity substrates will benefit broad applicationsin sensing and spectroscopy. [ABSTRACT FROM AUTHOR]

Wepresent metallic nanohole arrays fabricated on suspended membranesas an optofluidic substrate. Millimeter-sized suspended nanohole arrayswere fabricated using nanoimprint lithography. We demonstrate refractive-index-basedtuning of the optical spectra using a sucrose solution for the optimizationof SERS signal intensity, leading to a Raman enhancement factor of107. Furthermore, compared to dead-ended nanohole arrays,suspended nanohole arrays capable of flow-through detection increasedthe measured SERS signal intensity by 50 times. For directed transportof analytes, we present a novel methodology utilizing surface tensionto generate spontaneous flow through the nanoholes with flow ratesof 1 μL/min, obviating the need for external pumps or microfluidicinterconnects. Using this method for SERS, we obtained a 50 timeshigher signal as compared to diffusion-limited transport and coulddetect 100 pM 4-mercaptopyridine. The suspended nanohole substratespresented herein possess a uniform and reproducible geometry and showthe potential for improved analyte transport and SERS detection. [ABSTRACT FROM AUTHOR]