Smart Component for Switching of Plasmon Resonance by External Electric Field

Smart Modulators Based on Electric Field-Triggering of Surface Plasmon-Polariton for Active Plasmonics

Design and properties of a plasmonic modulator in situ tunable by electric field are presented. Our design comprises the creation of periodic surface pattern on the surface of an elastic polymer supported by a piezo-substrate by excimer laser irradiation and subsequent selective coverage by silver by tilted angle vacuum evaporation. The structure creation was confirmed by AFM and FIB-SEM techniques. An external electric field is used for fine control of the polymer pattern amplitude, which tends to decrease with increasing voltage. As a result, surface plasmon-polariton excitation is quenched, leading to the less pronounced structure of plasmon response. This quenching was checked using UV-Vis spectroscopy and SERS measurements, and confirmed by numerical simulation. All methods prove the proposed functionality of the structures enabling the creation smart plasmonic materials for a very broad range of advanced optical applications.

Physically Switchable Antimicrobial Surfaces and Coatings: General Concept and Recent Achievements

Bacterial environmental colonization and subsequent biofilm formation on surfaces represents a significant and alarming problem in various fields, ranging from contamination of medical devices up to safe food packaging. Therefore, the development of surfaces resistant to bacterial colonization is a challenging and actively solved task. In this field, the current promising direction is the design and creation of nanostructured smart surfaces with on-demand activated amicrobial protection. Various surface activation methods have been described recently. In this review article, we focused on the "physical" activation of nanostructured surfaces. In the first part of the review, we briefly describe the basic principles and common approaches of external stimulus application and surface activation, including the temperature-, light-, electric- or magnetic-field-based surface triggering, as well as mechanically induced surface antimicrobial protection. In the latter part, the recent achievements in the field of smart antimicrobial surfaces with physical activation are discussed, with special attention on multiresponsive or multifunctional physically activated coatings. In particular, we mainly discussed the multistimuli surface triggering, which ensures a better degree of surface properties control, as well as simultaneous utilization of several strategies for surface protection, based on a principally different mechanism of antimicrobial action. We also mentioned several recent trends, including the development of the to-detect and to-kill hybrid approach, which ensures the surface activation in a right place at a right time.

Soft optical metamaterials

Optical metamaterials consist of artificially engineered structures exhibiting unprecedented optical properties beyond natural materials. Optical metamaterials offer many novel functionalities, such as super-resolution imaging, negative refraction and invisibility cloaking. However, most optical metamaterials are comprised of rigid materials that lack tunability and flexibility, which hinder their practical applications. This limitation can be overcome by integrating soft matters within the metamaterials or designing responsive metamaterial structures. In addition, soft metamaterials can be reconfigured via optical, electrical, thermal and mechanical stimuli, thus enabling new optical properties and functionalities. This paper reviews different types of soft and reconfigurable optical metamaterials and their fabrication methods, highlighting their exotic properties. Future directions to employ soft optical metamaterials in next-generation metamaterial devices are identified.

Application of Plasmon-Induced Lithography for Creation of a Residual-Free Pattern and Simple Surface Modifications

Here, we propose a plasmon-induced redistribution of a thin polymer layer as a unique way for a residual layer-free lithographic approach. In particular, we demonstrate an ultrafast area-selective fabrication method using a low-intensity visible laser irradiation to direct the polymer mass flow, under the plasmon-active substrates. Plasmon-supported substrates were created by thermal annealing of Ag thin films and covered by thin polystyrene layers. Then, laser beam writing (LBW) was applied to introduce a surface tension gradient through the local plasmon heating. As a result, polystyrene was completely removed from the irradiated place, without any residual layer. The proposed approach does not require any additional development steps, such as solvent or plasma treatment. To demonstrate the advantages of the proposed technique, we implemented the LBW-patterned structures for further spatially selective surface functionalization, including the metal deposition, spontaneous thiol grafting, and electrochemical deposition of ordered polypyrrole array.

Metal-Enhanced Fluorescence Study in Aqueous Medium by Coupling Gold Nanoparticles and Fluorophores Using a Bilayer Vesicle Platform

Gold nanoparticles (AuNPs) display excellent plasmonic properties, which are expected to assist fluorescence enhancement for dyes, and the phenomenon is known as "metal-enhanced fluorescence" (MEF). In this study, we demonstrate AuNP-induced MEF for a modified bipyridine-based construct 4-(pyridine-2-yl)-3H-pyrrolo[2,3-c]quinoline (PPQ) when it binds with biologically important Zn2+. Importantly, this phenomenon is observed under aqueous conditions in a biocompatible bilayer vesicle platform. When PPQ binds with Zn2+ to form the complex in the presence of appropriate AuNPs, MEF is evident once compared with the fluorescence intensity in the absence of AuNPs. Among the three different sizes of AuNPs used, the enhancement is observed with an average diameter of 33 nm, whereas 18 and 160 nm do not show any enhancement. A possible mechanism is ascribed to the radiating plasmons of the AuNPs, which can couple with the emission frequencies of the fluorophore under a critical distance-dependent arrangement. We witness that the enhancement in fluorescence is accompanied with a reduction in lifetime components. It is proposed that the mechanism may be predominantly derived from the enhancement of an intrinsic radiative decay rate and partly from the localized electric field effect. Overall, this work shows a rational approach to design fluorophore-metal configurations with the desired emissive properties and a basis for a useful nanophotonic technology under biological conditions.

Surface Plasmon-Polariton: A Novel Way To Initiate Azide-Alkyne Cycloaddition

Plasmon catalysis has recently generated tremendous interest in the field of modern chemistry. Application of plasmon introduces the principally new stimulus for the activation of organic reactions, keeping the optical energy concentrated in the vicinity of plasmonic structure, creating an optical near-field enhancement as well as hot electron injection. In this work, for the first time, we presented a new way for the initiation of the azide-alkyne cycloaddition (AAC) using the surface plasmon-polariton wave, supported by the gold grating. With this concept in hand, the plasmon-active gold grating was functionalized with 4-ethynylbenzenediazonium compound. Then, surface-grafted 4-ethynylphenyl groups were plasmon activated and clicked with 4-azidobenzoic acid. Additional experiments allowed to exclude the potential effect of photon, heating, and metal impurities confirmed the key role of surface plasmon-polariton AAC activation. For the investigation of plasmon-induced AAC mechanism, 4-azidophenyl groups (instead of 4-ethynylphenyl groups) were also grafted to the grating surface. Further careful evaluation of reaction kinetics demonstrates that the AAC reaction rate is significantly higher in the case of acetylene activation than in the case of azide activation.

Smart, Piezo-Responsive Polyvinylidenefluoride/Polymethylmethacrylate Surface with Triggerable Water/Oil Wettability and Adhesion

The design of smart surfaces with externally triggerable water/oil wettability and adhesion represents one of the most up-to-date challenges in the field of material science. In this work, the intelligent surface with electrically triggerable wettability and water/oil adhesion is presented. As a basic material background exhibiting electric field (EF) sensitivity, the piezo-responsive polymethylmethacrylate/polyvinylidenefluoride polymer fibers were used. To expand the available range of water/oil contact angles (CAs) and adhesion, the fibers were grafted with hydrophilic or hydrophobic functional groups using diazonium chemistry. The fiber functionality was evaluated using the static CA and wettability hysteresis measurements (increasing/decreasing drop volume and tilting angles), drops adhesion/repellence and graphite self-cleaning test performed with and without the application of EF. It was found that the proposed method enables tuning the surface wettability in the superhydrophobic/superoleophobic-hydrophilic/oleophilic range and changing of surface properties from low adhesive to high adhesive for water and oil. More convincing results were achieved in the case of fiber surface modification by ADT-C₈F₁₇, which may result from a rearrangement of the grated -C₆H₄C₈F₁₇ functional group under the application of EF triggering. Moreover, the triggering which can be performed in the extremely fast way (the surface responds to the EF switching on/off in seconds) was found to be fully reversible. Finally, the additional tests indicate the satisfactory stability of created fiber-based coating against the mechanical treatment.

Tailored Surfaces/Assemblies for Molecular Plasmonics and Plasmonic Molecular Electronics

Molecular plasmonics uses and explores molecule-plasmon interactions on metal nanostructures for spectroscopic, nanophotonic, and nanoelectronic devices. This review focuses on tailored surfaces/assemblies for molecular plasmonics and describes active molecular plasmonic devices in which functional molecules and polymers change their structural, electrical, and/or optical properties in response to external stimuli and that can dynamically tune the plasmonic properties. We also explore an emerging research field combining molecular plasmonics and molecular electronics.

Sandwiched gold/PNIPAm/gold microstructures for smart plasmonics application: towards the high detection limit and Raman quantitative measurements

A smart plasmonic SERS platform, comprising a layer of a stimuli-responsive polymer sandwiched between two gold layers, is reported.

Ultrasensitive and reproducible SERS platform of coupled Ag grating with multibranched Au nanoparticles

The ultra high sensitive and reproducible surface enhanced Raman substrate has been made through the immobilization of sharp-edges specific gold nanoparticles on the silver grating surface.