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The sensitivity in surface enhanced infrared spectroscopy (SEIRS) strongly depends on where the resonant excitation is spectrally located compared to the molecular vibration that is to be enhanced. In this contribution, we study the effect of coupling in the electromagnetic properties of 2D gold nanorod arrays in the IR. We also study the SEIRS activity of higher order resonant excitations in long nanoantennas to identify polaritonic signals of a supporting SiO2 layer with nanometer thickness (3 nm) on a silicon substrate. [ABSTRACT FROM AUTHOR]

We report on the observation of second-order infrared (IR) plasmon resonances in lithographically prepared gold nanorods investigated by means of far-field microscopic IR spectroscopy. In addition to the fundamental antennalike mode, even and odd higher order resonances are observed under normal incidence of light. The activation of even-order modes under normal incidence is surprising since even orders are dipole-forbidden because of their centrosymmetric charge density oscillation. Performing atomic force microscopy and calculations with the boundary element method, we determine that excitation of even modes is enabled by symmetry breaking by structural deviations of the rods from an ideal, straight shape. [ABSTRACT FROM AUTHOR]

With infrared spectroscopic microscopy using synchrotron radiation, we systematically studied resonant light scattering from electron-beam lithographically produced gold nanowires (nanostripes) with diameters in the 100 nm range and with various lengths below 1 to about 2.5 μm. Similar to electrochemically grown cylindrical wires of high crystalline quality, clear antennalike plasmon resonances were observed for these stripelike and less-perfect wires. The resonance wavelength shifts with length as theoretically predicted for cylindrical gold antennas in the optical range. Surprisingly, also the extinction cross section of the nanostripes is equal to that measured for highly crystalline cylinders. [ABSTRACT FROM AUTHOR]

The formation of self-assembled Pb nanorods on a vicinal Si(335)/Au surface at 305 K was monitored in situ with polarization dependent infrared spectroscopy. The rods have formed from Pb evaporated on a single domain Au-stabilized Si(335) surface under ultrahigh vacuum conditions and reached lengths of about 1 μm. As the rods are aligned almost parallel, a large optical anisotropy of the transmitted infrared light was detected. A plasmonic antennalike resonance appeared in the spectra. Since such resonance frequencies are mainly determined by the length of the rods, the growth process was directly monitored via the shift of the resonance frequency. The estimated extinction cross section at resonance frequency indicates field enhancement similar to that observed for gold nanorods. [ABSTRACT FROM AUTHOR]

With infrared spectroscopic microscopy using synchrotron light, the authors studied resonant light scattering from single metal nanowires with diameters in the 100 nm range and with lengths of a few microns. The Au and Cu nanowires were electrochemically grown in polycarbonate etched ion-track membranes and transferred on infrared-transparent substrates. Significant antennalike plasmon resonances were observed in good agreement with exact light-scattering calculations. The resonances depend not only on length and diameter but also on the dielectric surrounding of the nanowire. The observed maximum extinction at resonance corresponds to an electromagnetic far-field enhancement by a factor of about 5. [ABSTRACT FROM AUTHOR]

Theory predicts a distinct spectral shift between the near- and far-field optical response of plasmonic antennas. Here we combine near-field optical microscopy and far-field spectroscopy of individual infrared-resonant nanoantennas to verify experimentally this spectral shift. Numerical calculations corroborate our experimental results. We furthermore discuss the implications of this effect in surface-enhanced infrared spectroscopy. [ABSTRACT FROM AUTHOR]

Conducting polymers have emerged as promising active materials for metasurfaces due to their electrically tunable states and large refractive index modulation. However, existing approaches are often limited to infrared operation or single-polymer systems, restricting their versatility. In this Letter, we present organic metasurfaces featuring dual conducting polymers, polyaniline (PANI) and poly(3,4-ethylenedioxythiophene) (PEDOT), to achieve contrasting dynamic optical responses at visible frequencies. Sequential electrochemical polymerizations locally conjugate subwavelength-thin layers of PANI and PEDOT onto preselected gold nanorods, creating electro-plasmonic antennas with distinct optoelectronic properties. This dual-polymer approach enables dynamic metasurface pixel control without individual electrode routing, thereby simplifying active metasurface designs. The metasurfaces exhibit dual-channel functions, including anomalous transmission and holography, through the redox-state switching of both polymers. Our work underscores the potential of conducting polymers for active metasurface applications, offering a pathway to advanced reconfigurable optical devices at visible frequencies.

Metasurfaces have revolutionized optical technologies by offering powerful, compact, and versatile solutions to control light. Conducting polymers, characterized by their conjugated molecular structures, facilitate charge transport and exhibit interesting electrical, optical, and mechanical properties. Integrating conducting polymers with optical metasurfaces can unlock new opportunities and functionalities in modern optics. In this work, we demonstrate an electrochemically programmable metasurface with independently controlled metasurface pixels at optical frequencies. Electrochemical modulation of locally conjugated polyaniline on gold nanorods, which are arranged on addressable electrodes according to the Pancharatnam-Berry phase design, enables dynamic control over the metasurface pixels into programmable configurations. With the same metasurface device, we showcase diverse optical functions, including dynamic beam diffraction and varifocal lensing along and off the optical axis. The synergy between flat optics and conducting polymer science holds immense potential to enhance the performance and function versatility of metasurfaces, paving the way for innovative optical applications.

Coherent collective oscillations of electrons excited in metallic nanostructures (localized surface plasmons) can confine incident light to atomic scales and enable strong light-matter interactions, which depend nonlinearly on the local field. Direct sampling of such collective electron oscillations in real-time is crucial to performing petahertz scale optical modulation, control, and readout in a quantum nanodevice. Here, we demonstrate real-time tracking of collective electron oscillations in an Au bowtie nanoantenna, by recording photo-assisted tunnelling currents generated by such oscillations in this quantum nanodevice. The collective electron oscillations show a noninstantaneous response to the driving laser fields with a T 2 decay time of nearly 8 femtoseconds. The contributions of linear and nonlinear electron oscillations in the generated tunnelling currents were precisely determined. A phase control of electron oscillations in the nanodevice is illustrated. Functioning in ambient conditions, the excitation, phase control, and read-out of coherent electron oscillations pave the way toward on-chip light-wave electronics in quantum nanodevices., (© 2024. The Author(s).)

A general and quantitative method to characterize molecular transport in polymers with good temporal and high spatial resolution, in complex environments, is an important need of the pharmaceutical, textile, and food and beverage packaging industries, and of general interest to the polymer science community. Here we show how the amplified infrared (IR) absorbance sensitivity provided by plasmonic nanoantenna-based surface enhanced infrared absorption (SEIRA) provides such a method. SEIRA enhances infrared (IR) absorbances primarily within 50 nm of the nanoantennas, enabling localized quantitative detection of even trace quantities of analytes and diffusion measurements in even thin polymer films. Relative to a commercial attenuated total internal reflection (ATR) system, the limit of detection is enhanced at least 13-fold, and as is important for measuring diffusion, the detection volume is about 15 times thinner. Via this approach, the diffusion coefficient and solubility of specific molecules, including l-ascorbic acid (vitamin C), ethanol, various sugars, and water, in both simple and complex mixtures (e.g., beer and a cola soda), were determined in poly(methyl methacrylate), high density polyethylene (HDPE)-based, and polypropylene-based polyolefin films as thin as 250 nm.

Recently in nanophotonics, a rigorous evolution from passive to active metasurfaces has been witnessed. This advancement not only brings forward interesting physical phenomena but also elicits opportunities for practical applications. However, active metasurfaces operating at visible frequencies often exhibit low performance due to design and fabrication restrictions at the nanoscale. In this work, we demonstrate electrochemically controlled metasurfaces with high intensity contrast, fast switching rate, and excellent reversibility at visible frequencies. We use a conducting polymer, polyaniline (PANI), that can be locally conjugated on preselected gold nanorods to actively control the phase profiles of the metasurfaces. The optical responses of the metasurfaces can be in situ monitored and optimized by controlling the PANI growth of subwavelength dimension during the electrochemical process. We showcase electrochemically controlled anomalous transmission and holography with good switching performance. Such electrochemically powered optical metasurfaces lay a solid basis to develop metasurface devices for real-world optical applications., (Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)

Reversible hydrogen uptake and the metal/dielectric transition make the Mg/MgH 2 system a prime candidate for solid-state hydrogen storage and dynamic plasmonics. However, high dehydrogenation temperatures and slow dehydrogenation hamper broad applicability. One promising strategy to improve dehydrogenation is the formation of metastable γ-MgH 2 . A nanoparticle (NP) design, where γ-MgH 2 forms intrinsically during hydrogenation is presented and a formation mechanism based on transmission electron microscopy results is proposed. Volume expansion during hydrogenation causes compressive stress within the confined, anisotropic NPs, leading to plastic deformation of β-MgH 2 via (301) β twinning. It is proposed that these twins nucleate γ-MgH 2 nanolamellas, which are stabilized by residual compressive stress. Understanding this mechanism is a crucial step toward cycle-stable, Mg-based dynamic plasmonic and hydrogen-storage materials with improved dehydrogenation. It is envisioned that a more general design of confined NPs utilizes the inherent volume expansion to reform γ-MgH 2 during each rehydrogenation., (© 2021 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

Reconfigurable optical systems are the object of continuing, intensive research activities, as they hold great promise for realizing a new generation of compact, miniaturized, and flexible optical devices. However, current reconfigurable systems often tune only a single state variable triggered by an external stimulus, thus, leaving out many potential applications. Here we demonstrate a reconfigurable multistate optical system enabled by phase transitions in vanadium dioxide (VO 2 ). By controlling the phase-transition characteristics of VO 2 with simultaneous stimuli, the responses of the optical system can be reconfigured among multiple states. In particular, we show a quadruple-state dynamic plasmonic display that responds to both temperature tuning and hydrogen-doping. Furthermore, we introduce an electron-doping scheme to locally control the phase-transition behavior of VO 2 , enabling an optical encryption device encoded by multiple keys. Our work points the way toward advanced multistate reconfigurable optical systems, which substantially outperform current optical devices in both breadth of capabilities and functionalities., Competing Interests: The authors declare no competing financial interest., (© 2020 American Chemical Society.)

Molecular chirality is a geometric property that is of great importance in chemistry, biology, and medicine. Recently, plasmonic nanostructures that exhibit distinct chiroptical responses have attracted tremendous interest, given their ability to emulate the properties of chiral molecules with tailored and pronounced optical characteristics. However, the optical chirality of such human-made structures is in general static and cannot be manipulated postfabrication. Herein, different concepts to reconfigure the chiroptical responses of plasmonic nano- and micro-objects are outlined. Depending on the utilized strategies and stimuli, the chiroptical signature, the 3D structural conformation, or both can be reconfigured. Optical devices based on plasmonic nanostructures with reconfigurable chirality possess great potential in practical applications, ranging from polarization conversion elements to enantioselective analysis, chiral sensing, and catalysis., (© 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Displays are an indispensable medium to visually convey information in our daily life. Although conventional dye-based color displays have been rigorously advanced by world leading companies, critical issues still remain. For instance, color fading and wavelength-limited resolution restrict further developments. Plasmonic colors emerging from resonant interactions between light and metallic nanostructures can overcome these restrictions. With dynamic characteristics enabled by functional materials, dynamic plasmonic coloration may find a variety of applications in display technologies. In this review, we elucidate basic concepts for dynamic plasmonic color generation and highlight recent advances. In particular, we devote our review to a selection of dynamic controls endowed by functional materials, including magnesium, liquid crystals, electrochromic polymers, and phase change materials. We also discuss their performance in view of potential applications in current display technologies., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)

Selective transport and concentration of molecules to specified regions on a substrate both enhances the potential to detect such molecules and provides a path to spatially localize such molecules prior to initiation of subsequent chemical reactions. Here, we first embed radially symmetric α-, β-, and γ-cyclodextrin gradients in a hydrogel matrix. Driven by host-guest interactions between the cyclodextrins and the target molecule, we observe these gradients can serve to direct 2D molecular transport. Using xanthene dyes and organophosphates as target molecules, we found the transport metrics, e.g., selectivity, rate, and concentration limits, are strongly dependent on the specific cyclodextrin forming the gradient. In all cases, as the concentrating power of the gradient increased, the rate of target concentration slowed, which we hypothesize is because stronger interactions between the target and the cyclodextrin decrease the rate of target diffusion. The concentration enhancement for the nerve agent simulant 4-methylumbelliferyl phosphate (15.8) is the greatest when the gradient is formed using β-cyclodextrin while directed concentration of cyanomethyl phosphonate, a smaller non-aromatic organophosphate, is observed only for the smaller α-CD. To provide a near real-time read-out of the concentration of the analyte, we used an array of IR resonant metallic nanoantennas tuned to a specific IR absorption band of the analyte to enhance the IR signal generated by the analyte., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Proteins perform a variety of essential functions in living cells and thus are of critical interest for drug delivery as well as disease biomarkers. The different functions are derived from a hugely diverse set of structures, fueling interest in their conformational states. Surface-enhanced infrared absorption spectroscopy has been utilized to detect and discriminate protein monomers. As an important step forward, we are investigating collagen peptides consisting of  a  triple helix. While they constitute the main structural building blocks in many complex proteins, they are also a perfect model system for the complex proteins relevant in biological systems. Their complex spectroscopic information as well as the overall small size present a significant challenge for their detection and discrimination. Using resonant plasmonic nanoslits, which are known to show larger specificity compared to nanoantennas, we overcome this challenge. We perform in vitro surface-enhanced absorption spectroscopy studies and track the conformational changes of these collagen peptides under two different external stimuli, which are temperature and chemical surroundings. Modeling the coupling between the amide I vibrational modes and the plasmonic resonance, we can extract the conformational state of the collages and thus monitor the folding and unfolding dynamics of even a single monolayer. This leads to new prospects in studies of single layers of proteins and their folding behavior in minute amounts in a living environment.

Monosaccharides, which include the simple sugars such as glucose and fructose, are among the most important carbohydrates in the human diet. Certain chronic diseases, e.g., diabetes mellitus, are associated with anomalous glucose blood levels. Detecting and measuring the levels of monosaccharides in vivo or in aqueous solutions is thus of the utmost importance in life science, health, and point-of-care applications. Noninvasive sensing would avoid problems such as pain and potential infection hazards. Here, with the help of surface enhanced infrared absorption (SEIRA) spectroscopy, we demonstrate the reliable optical detection in the mid-infrared spectral range of pure glucose and fructose solutions as well as mixtures of both in aqueous solution. We utilize a reflection flow cell geometry with physiologically relevant concentrations as small as 10 g/L. As significant improvement over the standard baseline correction employed in SEIRA applications, we utilize principal component analysis (PCA) as machine learning algorithm, which is ideally suited for the extraction of vibrational data. We anticipate our results as important step in biosensing applications that will stimulate efforts to further improve the employed SEIRA substrates, the noise level of the spectroscopic light source, as well as the flow cell environment en route to significantly higher sensitivities and quantitative analysis, even in tear drops.

Proteins and peptides play a predominant role in biochemical reactions of living cells. In these complex environments, not only the constitution of the molecules but also their three-dimensional configuration defines their functionality. This so-called secondary structure of proteins is crucial for understanding their function in living matter. Misfolding, for example, is suspected as the cause of neurodegenerative diseases such as Alzheimer's and Parkinson's disease. Ultimately, it is necessary to study a single protein and its folding dynamics. Here, we report a first step in this direction, namely ultrasensitive detection and discrimination of in vitro polypeptide folding and unfolding processes using resonant plasmonic nanoantennas for surface-enhanced vibrational spectroscopy. We utilize poly-l-lysine as a model system which has been functionalized on the gold surface. By in vitro infrared spectroscopy of a single molecular monolayer at the amide I vibrations we directly monitor the reversible conformational changes between α-helix and β-sheet states induced by controlled external chemical stimuli. Our scheme in combination with advanced positioning of the peptides and proteins and more brilliant light sources is highly promising for ultrasensitive in vitro studies down to the single protein level.

Background: Peripheral sensory nerve injuries present a significant yet common challenge in acute hand trauma surgery. Standard treatment remains microsurgical end-to-end nerve repair where appropriate. Permanent loss of sensitivity and painful neuroma formation are typical sequelae of unsuccessful surgery. The objective of this study was to evaluate whether the additional use of a chitosan nerve tube in primary nerve repair positively influences sensory recovery., Methods: A randomized, controlled, two-center trial with parallel group design and double-blind assessment was conducted to demonstrate the superiority of the additional use of a chitosan nerve tube compared with microsurgical nerve repair alone. Seventy-four participants were enrolled. The primary outcome parameter used was degree of static two-point discrimination at 6 months after surgery. Additional secondary outcome parameters included filament recognition testing (Semmes-Weinstein); pain; neuroma development; and the Disabilities of the Arm, Shoulder and Hand score., Results: Nerve repair with additional use of chitosan nerve tubes (intervention group) significantly increased both tactile gnosis (expressed by two-point discrimination) and sensitivity (expressed by Semmes-Weinstein testing). The mean two-point discrimination at 6-month follow-up was 8 mm (range, 2 to 20 mm) in the control group and 6.3 mm (range, 1 to 15 mm) in the intervention group, respectively (p = 0.029). Two-point discrimination correlated with the Disabilities of the Arm, Shoulder and Hand score. In the control and intervention groups, respectively, three versus zero neuromas were found., Conclusions: Peripheral sensory nerve regeneration can be improved significantly by additional use of a chitosan nerve tube. An improved ability of static two-point discrimination is clinically relevant., Clinical Question/level of Evidence: Therapeutic, I.

Metasurfaces enable manipulation of light propagation at an unprecedented level, benefitting from a number of merits unavailable to conventional optical elements, such as ultracompactness, precise phase and polarization control at deep subwavelength scale, and multifunctionalities. Recent progress in this field has witnessed a plethora of functional metasurfaces, ranging from lenses and vortex beam generation to holography. However, research endeavors have been mainly devoted to static devices, exploiting only a glimpse of opportunities that metasurfaces can offer. We demonstrate a dynamic metasurface platform, which allows independent manipulation of addressable subwavelength pixels at visible frequencies through controlled chemical reactions. In particular, we create dynamic metasurface holograms for advanced optical information processing and encryption. Plasmonic nanorods tailored to exhibit hierarchical reaction kinetics upon hydrogenation/dehydrogenation constitute addressable pixels in multiplexed metasurfaces. The helicity of light, hydrogen, oxygen, and reaction duration serve as multiple keys to encrypt the metasurfaces. One single metasurface can be deciphered into manifold messages with customized keys, featuring a compact data storage scheme as well as a high level of information security. Our work suggests a novel route to protect and transmit classified data, where highly restricted access of information is imposed.

Background: Vascularized composite allotransplantation (VCA) is a rapidly expanding field of transplantation and provides a potential treatment for complex tissue defects. Peripheral blood mononuclear cells (PBMCs) shortly incubated with the antibiotic and chemotherapeutic agent mitomycin C (MMC) can suppress allogeneic T cell response and control allograft rejection in various organ transplantation models. MMC-incubated PBMCs (MICs) are currently being tested in a phase I clinical trial in kidney transplant patients. Previous studies with MICs in a complex VCA model showed the immunomodulatory potential of these cells. The aim of this study is to optimize and evaluate the use of MICs in combination with a standard immunosuppressive drug in VCA., Methods: Fully mismatched rats were used as hind limb donors [Lewis (RT1 1 )] and recipients [Brown-Norway (RT1 n )]. Sixty allogeneic hind limb transplantations were performed in six groups. Group A received donor-derived MICs combined with a temporary ciclosporin A (CsA) treatment. Group B received MICs in combination with a temporarily administered reduced dose of CsA. Group C served as a control and received a standard CsA dose temporarily without an additional administration of MICs, whereas Group D was solely medicated with a reduced CsA dose. Group E received no immunosuppressive therapy, neither CsA nor MICs. Group F was given a continuous standard immunosuppressive regimen consisting of CsA and prednisolone. The endpoint of the study was the onset of allograft rejection which was assessed clinically and histologically., Results: In group A and B, the rejection-free interval of the allograft was significantly prolonged to an average of 23.1 ± 1.7 and 24.7 ± 1.8 days compared to the corresponding control groups (p < 0.01). Rejection in groups C, D, and E was noted after 14.3 ± 1.1, 7.8 ± 0.7, and 6.9 ± 0.6 days. No rejection occurred in control group F during the follow-up period of 100 days. No adverse events have been noted., Conclusion: The findings of this study show that the combination of MICs with a temporary CsA treatment significantly prolongs the rejection-free interval in a complex VCA model. The combination of MICs with CsA showed no adverse events such as graft-versus-host disease. MICs, which are generated by a simple and reliable in vitro technique, represent a potential therapeutic tool for prolonging allograft survival through immunomodulation.

In this article, a chiral plasmonic hydrogen-sensing platform using palladium-based nanohelices is demonstrated. Such 3D chiral nanostructures fabricated by nanoglancing angle deposition exhibit strong circular dichroism both experimentally and theoretically. The chiroptical properties of the palladium nanohelices are altered upon hydrogen uptake and sensitively depend on the hydrogen concentration. Such properties are well suited for remote and spark-free hydrogen sensing in the flammable range. Hysteresis is reduced, when an increasing amount of gold is utilized in the palladium-gold hybrid helices. As a result, the linearity of the circular dichroism in response to hydrogen is significantly improved. The chiral plasmonic sensor scheme is of potential interest for hydrogen-sensing applications, where good linearity and high sensitivity are required., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We demonstrate surface enhanced infrared absorption spectroscopy using 1-dimensional highly doped semiconductors based on Si-doped InAsSb plasmonic nano-antennas. Engineering the plasmonic array to support the localized surface plasmon resonance aligned with the molecular vibrational absorption mode of interest involves finely setting the doping level and nano-antenna width. Heavily doped nano-antennas require a wider size compared to lightly doped resonators. Increasing the doping level, and consequently the width of the nano-antenna, enhances the vibrational absorption of a ~15 nm thick organic layer up to 2 orders of magnitude compared to the unstructured sample and therefore improves sensing. These results pave the way towards molecule fingerprint sensor manufacturing by tailoring the plasmonic resonators to get a maximum surface enhanced infrared absorption at the target vibrational mode.

High-resolution multicolor printing based on pixelated optical nanostructures is of great importance for promoting advances in color display science. So far, most of the work in this field has been focused on achieving static colors, limiting many potential applications. This inevitably calls for the development of dynamic color displays with advanced and innovative functionalities. In this Letter, we demonstrate a novel dynamic color printing scheme using magnesium-based pixelated Fabry-Pérot cavities by gray scale nanolithography. With controlled hydrogenation and dehydrogenation, magnesium undergoes unique metal and dielectric transitions, enabling distinct blank and color states from the pixelated Fabry-Pérot resonators. Following such a scheme, we first demonstrate dynamic Ishihara plates, in which the encrypted images can only be read out using hydrogen as information decoding key. We also demonstrate a new type of dynamic color generation, which enables fascinating transformations between black/white printing and color printing with fine tonal tuning. Our work will find wide-ranging applications in full-color printing and displays, colorimetric sensing, information encryption and anticounterfeiting.

Spectroscopic infrared chemical imaging is ideally suited for label-free and spatially resolved characterization of molecular species, but often suffers from low infrared absorption cross sections. Here, we overcome this limitation by utilizing confined electromagnetic near-fields of resonantly excited plasmonic nanoantennas, which enhance the molecular absorption by orders of magnitude. In the experiments, we evaporate microstructured chemical patterns of C 60 and pentacene with nanometer thickness on top of homogeneous arrays of tailored nanoantennas. Broadband mid-infrared spectra containing plasmonic and vibrational information were acquired with diffraction-limited resolution using a two-dimensional focal plane array detector. Evaluating the enhanced infrared absorption at the respective frequencies, spatially resolved chemical images were obtained. In these chemical images, the microstructured chemical patterns are only visible if nanoantennas are used. This confirms the superior performance of our approach over conventional spectroscopic infrared imaging. In addition to the improved sensitivity, our technique provides chemical selectivity, which would not be available with plasmonic imaging that is based on refractive index sensing. To extend the accessible spectral bandwidth of nanoantenna-enhanced spectroscopic imaging, we employed nanostructures with dual-band resonances, providing broadband plasmonic enhancement and sensitivity. Our results demonstrate the potential of nanoantenna-enhanced spectroscopic infrared chemical imaging for spatially resolved characterization of organic layers with thicknesses of several nanometers. This is of potential interest for medical applications which are currently hampered by state-of-art infrared techniques, e.g., for distinguishing cancerous from healthy tissues.

Infrared spectroscopy is a powerful tool widely used in research and industry for a label-free and unambiguous identification of molecular species. Inconveniently, its application to spectroscopic analysis of minute amounts of materials, for example, in sensing applications, is hampered by the low infrared absorption cross-sections. Surface-enhanced infrared spectroscopy using resonant metal nanoantennas, or short "resonant SEIRA", overcomes this limitation. Resonantly excited, such metal nanostructures feature collective oscillations of electrons (plasmons), providing huge electromagnetic fields on the nanometer scale. Infrared vibrations of molecules located in these fields are enhanced by orders of magnitude enabling a spectroscopic characterization with unprecedented sensitivity. In this Review, we introduce the concept of resonant SEIRA and discuss the underlying physics, particularly, the resonant coupling between molecular and antenna excitations as well as the spatial extent of the enhancement and its scaling with frequency. On the basis of these fundamentals, different routes to maximize the SEIRA enhancement are reviewed including the choice of nanostructures geometries, arrangements, and materials. Furthermore, first applications such as the detection of proteins, the monitoring of dynamic processes, and hyperspectral infrared chemical imaging are discussed, demonstrating the sensitivity and broad applicability of resonant SEIRA.

Finger replantations demand technical excellence in microsurgery and hand trauma care. The objective of this study was to determine whether finger replantations constitute an appropriate and safe procedure for residency training. Additionally, the prognostic risk factors for the need to take a replanted finger back to the operation room and replant failure were analyzed.All patients who underwent finger replantation after complete amputation between 2007 and 2015 were included in a retrospective comparative study. These patients were either treated by an attending plastic surgeon (cohort 1) or by a postgraduate year 5 or 6 resident under supervision (cohort 2). Logistic regression analysis was used to identify the prognostic risk factors for emergent take backs and replant failures.A total of 109 completely amputated fingers were replanted in 89 patients. Fifty-seven digits were replanted in cohort 1, and 52 digits were replanted in cohort 2. Patient demographic data revealed an equal distribution between the two cohorts with an overall finger-replantation success rate of 67.0%. The prognostic risk factors related to increased take back and replant failure rates were fewer than two venous anastomoses (take back odds ratio [AOR], 0.27; confidence interval (CI), 0.12-0.63; and replant failure AOR, 0.21; 95% CI, 0.08-0.55) and intraoperative noticeable problems regarding the vascular anastomoses (take back AOR, 2.26; 95% CI, 0.96-5.33 and replant failure AOR, 2.45; 95% CI, 1.00-6.00). The type of surgeon did not exhibit an influence on the risk of take back (OR, 1.14; 95% CI, 0.53-2.41) or replant failure (OR, 1.03; 95% CI, 0.46-2.30). Similarly, after adjusting for all risk factors, the risks for take backs (AOR, 1.04; 95% CI, 0.46-2.36) and replant failures (AOR, 0.91; 95% CI, 0.38-2.19) did not differ between the 2 cohorts.Finger replantations can be applied as a safe procedure in residency training under standardized conditions and do not negatively affect quality of care. Technical proficiency in microsurgery and elective and trauma hand care as well as supervision by an experienced plastic or hand surgeon are mandatory. Regardless of the surgeons' experience, fewer than 2 venous anastomoses and the presence of intraoperative vascular anomalies represent significant prognostic risk factors for postoperative complications.

Purpose: The clinical course after major burns is characterized by microcirculatory changes and consecutive capillary leakage. However, current clinical monitoring does not properly assess microcirculation, whereas macrohemodynamic changes are continuously evaluated. Here, we assess if macrohemodynamic and microhemodynamic parameters after burn trauma are correlated in a rat model., Methods: Burn plasma harvested from donor rats 4 hours after thermal injury (30% total body surface area, 100 °C water, 12 seconds) was administered intravenously to healthy animals during 2 hours of intravital microscopy (burn group [BG]). Shamburn plasma (same procedure but water at 37°C) was transferred for negative controls (shamburn group [SBG]). Intravital microscopy was performed at 0, 60, and 120 minutes to assess capillary leakage measuring fluorescein isothiocyanate-albumin extravasation. Macrocirculation was assessed using mean arterial pressure and heart rate, whereas microcirculation was evaluated using red blood cell velocity, venular diameter, venular wall shear rate and plasma extravasation at 0, 60, and 120 minutes in postcapillary venules., Results: Thirty mesenteric venules (16 animals) in SBG and 31 mesenteric venules (15 animals) in BG were observed during intravital microscopy. Mean arterial pressure and heart rate remained within acceptable margins and showed no significant differences, neither within nor between groups. Significant correlations between macrohemodynamic and microhemodynamic conditions were neither observed for BG nor SBG, except from a significant correlation of MAP and plasma extravasation at T60. However, at T120 mesenteric venules in the BG clearly showed microvascular burn edema, whereas venules in SBG did not., Conclusions: Stabilization of macrohemodynamic conditions may not necessarily have positive effects on microcirculatory derangements-a fact that has not been shown for burns yet, that is-however, well described for sepsis. Further studies are required to show whether distinct monitoring of microcirculation may offer new approaches for burn trauma treatment.

We perform far-field spectroscopy of infrared metal antennas on silicon oxide layers of different thickness, where we find a splitting of the plasmonic resonance. This splitting can result in a transparency window, corresponding to suppression of antenna scattering, respectively "cloaking" of the antenna. Backed up by theory, we show that this effect is caused by strong coupling between the metal antenna plasmons and the surface phonon polaritons in the oxide layer. The effect is a kind of induced transparency in which the strength of the phonon-polariton field plays the crucial role. It represents a further tuning possibility for the optical performance of infrared devices.

Background: Bioethanol-fueled fireplaces are popular interior home decoration accessories. Although their safety is promoted frequently, actual presentations of severe burn injuries in our burn intensive care unit (ICU) have focused the authors on safety problems with these devices. In this article we want to explore the mechanisms for these accidents and state our experiences with this increasingly relevant risk for severe burn injuries., Materials and Methods: The computerized medical records of all burn intensive care patients in our burn unit between 2000 and 2014 were studied. Since 2010, 12 patients with bioethanol associated burn injuries were identified. Their data was compared to the values of all patients, except the ones injured by bioethanol fireplaces that presented themselves to our burn ICU between the years 2010 and 2014., Results: At time of admission the bioethanol patients had a mean ABSI-score of 4.8 (+/- 2.2 standard deviation (SD)). A mean of 17 percent (+/- 9.1 SD) body surface area was burned. Involvement of face and hands was very common. An operative treatment was needed in 8 cases. A median of 20 days of hospitalization (range 3-121) and a median of 4.5 days on the ICU (range 1-64) were necessary. No patient died. In most cases the injuries happened while refilling or while starting the fire, even though safety instructions were followed. In the control group, consisting of 748 patients, the mean ABSI-score was 5.6 (+/- 2.7 SD). A mean of 16.5 percent (+/- 10.1 SD) body surface area was burned. Treatment required a median of 3 days on the burn ICU (range 1-120). Regarding these parameters, the burden of disease was comparable in both groups., Conclusion: Bioethanol-fueled fireplaces for interior home decoration are a potential source for severe burn accidents even by intended use., (Copyright © 2015 Elsevier Ltd and ISBI. All rights reserved.)

Background: Complex peripheral nerve injuries of the hand include at least 300,000 cases per year in Europe. The standard treatment involves a microsurgical end-to-end suture of traumatic sensory nerve lesions of the hand without a gap. The objective of this study protocol is to evaluate whether the additional use of a chitosan nerve tube in primary repair of traumatic sensory nerve lesions of the hand without a gap has an effect on the recovery of sensitivity., Methods/design: We planned a randomized double-blind controlled multicenter trial with a parallel group design in order to show superiority for the additional use of a chitosan nerve tube. This study will enroll 100 participants with traumatic sensory nerve lesions of the hand without a gap from three Trauma Care Centers. Participants will be randomized in a 1:1 ratio to primary microsurgical repair of the injured nerve with the additional use of a chitosan nerve tube or direct tension free microsurgical repair of the injured nerve alone. The static two-point discrimination of the injured finger after 6 months will be the primary outcome parameter., Discussion: In the proposed study, the additional use of a chitosan nerve tube for a primary microsurgical repair of traumatic sensory nerve lesions of the hand without a gap will be evaluated in a prospective randomized double-blind controlled multicenter trial for the first time to create the highest possible evidence for the procedure., Trial Registration: ClinicalTrials.gov Identifier: NCT02372669 . Protocol Registration Receipt on 27 February 2015.

We report on the impact of the differing spectral near- and far-field properties of resonantly excited gold nanoantennas on the vibrational signal enhancement in surface-enhanced infrared absorption (SEIRA). The knowledge on both spectral characteristics is of considerable importance for the optimization of plasmonic nanostructures for surface-enhanced spectroscopy techniques. From infrared micro-spectroscopic measurements, we simultaneously obtain spectral information on the plasmonic far-field response and, via SEIRA spectroscopy of a test molecule, on the near-field enhancement. The molecular test layer of 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP) was deposited on the surface of gold nanoantennas with different lengths and thus different far-field resonance energies. We carefully studied the Fano-type vibrational lines in a broad spectral window, in particular, how the various vibrational signals are enhanced in relation to the ratio of the far-field plasmonic resonance and the molecular vibrational frequencies. As a detailed experimental proof of former simulation studies, we show the clearly red-shifted maximum SEIRA enhancement compared to the far-field resonance.

A switchable perfect absorber with multispectral thermal imaging capability is presented. Aluminum nanoantenna arrays above a germanium antimony telluride (GST) spacer layer and aluminum mirror provide efficient wavelength-tunable absorption in the mid-infrared. Utilizing the amorphous-to-crystalline phase transition in GST, this device offers switchable absorption with strong reflectance contrast at resonance and large phase-change-induced spectral shifts., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We demonstrate highly sensitive infrared spectroscopy of sample volumes close to the diffraction limit by coupling a femtosecond fiber-feedback optical parametric oscillator (OPO) to a conventional Fourier-transform infrared (FTIR) spectrometer. The high brilliance and long-term stable infrared radiation with 1e(2)-bandwidths up to 125 nm is easily tunable between 1.4 μm and 4.2 μm at 43 MHz repetition rate and thus enables rapid and low-noise infrared spectroscopy. We demonstrate this by measuring typical molecular vibrations in the range of 3 μm. Combined with surface-enhanced infrared spectroscopy, where the confined electromagnetic near-fields of resonantly excited metal nanoparticles are employed to enhance molecular vibrations, we realize the spectroscopic detection of a molecular monolayer of octadecanethiol. In comparison to conventional light sources and synchrotron radiation, our compact table-top OPO system features a significantly improved performance making it highly suitable for rapid analysis of minute amounts of molecular species in life science and medicine laboratories.

Infrared vibrations of molecular species can be enhanced by several orders of magnitude with plasmonic nanoantennas. Based on the confined electromagnetic near-fields of resonantly excited metal nanoparticles, this antenna-assisted surface-enhanced infrared spectroscopy enables the detection of minute amounts of analytes localized in the nanometer-scale vicinity of the structure. Among other important parameters, the distance of the vibrational oscillator of the analyte to the nanoantenna surface determines the signal enhancement. For sensing applications, this is a particularly important issue since the vibrating dipoles of interest may be located far away from the antenna surface because of functional layers and the large size of biomolecules, proteins, or bacteria. The relation between distance and signal enhancement is thus of paramount importance and measured here with in situ infrared spectroscopy during the growth of a probe layer. Our results indicate a diminishing signal enhancement and the effective saturation of the plasmonic resonance shift beyond 100 nm. The experiments carried out under ultra-high-vacuum conditions are supported by numerical calculations.

We report on the near-field coupling of individual gold nanoantennas arranged in tip-to-tip dimer configuration, leading to strong electromagnetic field enhancements in the infrared, which is of great interest for sensing applications such as surface-enhanced infrared spectroscopy. We quantitatively evaluated the enhancement of vibrational excitations of a 5 nm thick test layer of 4,4'-bis(N-carbazolyl)-1,1'-biphenyl as a function of different gap sizes. The dimers with the smallest gaps under investigation (∼3 nm) lead to more than 1 order of magnitude higher signal enhancement with respect to gaps of 50 nm width. The comparison of experimental data and finite-difference time-domain simulations reveals a nonperfect filling of the gaps with sizes below 10 nm, which means that morphological information on the nanoscale is obtained additionally to chemical information.

Many nano-optical applications require a suitable nanofabrication technology. Hole-mask colloidal nanolithography has proven to be a low-cost and large-area alternative for the fabrication of complex plasmonic nanostructures as well as metamaterials. In this paper, we describe the fabrication process step by step. We manufacture a variety of different plasmonic structures ranging from simple nano-antennas over complex chiral structures to stacked composite materials for applications such as sensing. Additionally, we give details on the control of the nanostructure lateral density which allows for the multilayer-fabrication of complex nanostructures. In two accompanying movies, the fabrication strategy is explained and details are being demonstrated in the lab. The movies can be found at the website of Beilstein TV.

A key challenge for the development of active plasmonic nanodevices is the lack of materials with fully controllable plasmonic properties. In this work, we demonstrate that a plasmonic resonance in top-down nanofabricated yttrium antennas can be completely and reversibly turned on and off using hydrogen exposure. We fabricate arrays of yttrium nanorods and optically observe, in extinction spectra, the hydrogen-induced phase transition between the metallic yttrium dihydride and the insulating trihydride. Whereas the yttrium dihydride nanostructures exhibit a pronounced particle plasmon resonance, the transition to yttrium trihydride leads to a complete vanishing of the resonant behavior. The plasmonic resonance in the dihydride state can be tuned over a wide wavelength range by simply varying the size of the nanostructures. Furthermore, we develop an analytical diffusion model to explain the temporal behavior of the hydrogen loading and unloading trajectories observed in our experiments and gain information about the thermodynamics of our device. Thus, our nanorod system serves as a versatile basic building block for active plasmonic devices ranging from switchable perfect absorbers to active local heating control elements.