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Gold nanoparticles decorated with analyte recognition units can form the basis of colorimetric (bio)sensors. The presentation of those recognition units may play a critical role in determining sensor sensitivity. Herein, we use a model system to investigate the effect of the architecture of a polymeric linker that connects gold nanoparticles with the recognition units. Our results show that the number of the latter that can be adsorbed during the assembly of the colorimetric sensors depends on the linker topology. We also show that this may lead to substantial differences in colorimetric sensor performance, particularly in situations in which the interactions with the analyte are comparably weak. Finally, we discuss design principles for efficient colorimetric sensor materials based on our findings.

Nanoparticle tracking analysis (NTA) is a widely used methodology to investigate nanoscale systems at the single species level. Here, we introduce the locally structured on-chip optofluidic hollow-core light cage, as a novel platform for waveguide-assisted NTA. This hollow waveguide guides light by the antiresonant effect in a sparse array of dielectric strands and includes a local modification to realize aberration-free tracking of individual nano-objects, defining a novel on-chip solution with properties specifically tailored for NTA. The key features of our system are (i) well-controlled nano-object illumination through the waveguide mode, (ii) diffraction-limited and aberration-free imaging at the observation site, and (iii) a high level of integration, achieved by on-chip interfacing to fibers. The present study covers all aspects relevant for NTA including design, simulation, implementation via 3D nanoprinting, and optical characterization. The capabilities of the approach to precisely characterize practically relevant nanosystems have been demonstrated by measuring the solvency-induced collapse of a nanoparticle system which includes polymer brush-based shells that react to changes in the liquid environment. Our study unlocks the advantages of the light cage approach in the context of NTA, suggesting its application in various areas such as bioanalytics, life science, environmental science, or nanoscale material science in general.

Coupling of light from free space to optical fibers is essential for many applications, while commonly used step-index optical fibers provide insufficient coupling efficiencies especially at large ...

Tracking and analyzing the individual diffusion of nanoscale objects such as proteins and viruses is an important methodology in life science. Here, we show a sensor that combines the efficiency of light line illumination with the advantages of fluidic confinement. Tracking of freely diffusing nano-objects inside water-filled hollow core fibers with core diameters of tens of micrometers using elastically scattered light from the core mode allows retrieving information about the Brownian motion and the size of each particle of the investigated ensemble individually using standard tracking algorithms and the mean squared displacement analysis. Specifically, we successfully measure the diameter of every gold nanosphere in an ensemble that consists of several hundreds of 40 nm particles, with an individual precision below 17% (±8 nm). In addition, we confirm the relevance of our approach with respect to bioanalytics by analyzing 70 nm λ-phages. Overall these features, together with the strongly reduced demand for memory space, principally allows us to record thousands of frames and to achieve high frame rates for high precision tracking of nanoscale objects.

The focusing of light represents a key functionality, which can efficiently be achieved through wavefront shaping via metasurfaces (MSs). Remote light focusing requires interfacing these ultraflat photonic structures with optical fibers, which is hard to achieve due to fabrication limitations and challenging beam management. Herein, the successful interfacing of a focusing plasmonic metalens with a regular single‐mode step‐index fiber through modified electron beam lithography is demonstrated. Specifically, a plasmonic MS consisting of nanoslots is realized on the end face of a modified single‐mode fiber via planarization and e‐beam lithography. A key feature of the device is the introduction of a coreless glass section in between the fiber and MS, which allows for free beam expansion up to 48 μm to fully exploit the numerical aperture (NA) of the metalens. In agreement with simulations, a clear focus with a NA of about 0.3 is found in the experiments, confirming the successful realization of a plasmonic metalens‐enhanced single‐mode fiber. Due to its unique properties, this concept finds applications in a multitude of areas, examples of which include optical trapping, generation of sophisticated beam profiles, and boosting light coupling efficiencies.

The pressure-assisted melt filling technique (PAMFT) is promising approach for integrating new materials such as glasses or semiconductor into fiber, while only a small amount of starting material (

Accurate determination of the size distribution of nanoparticle ensembles remains a challenge in nanotechnology-related applications due to the limitations of established methods. Here, a microstructured fiber-assisted nanoparticle tracking analysis (FaNTA) realization is introduced that breaks existing limitations through the recording of exceptionally long trajectories of rapidly diffusing polydisperse nanoparticles, resulting in excellent sizing precision and unprecedented separation capabilities of bimodal nanoparticle mixtures. An effective-single-mode antiresonant-element fiber allows to efficiently confine nanoparticles in a light-guiding microchannel and individually track them over more than 1000 frames, while aberration-free imaging is experimentally confirmed by cross-correlation analysis. Unique features of the approach are (i) the highly precise determination of the size distribution of monodisperse nanoparticle ensembles (only 7% coefficient of variation) and (ii) the accurate characterization of individual components in a bimodal mixture with very close mean diameters, both experimentally demonstrated for polymer nanospheres. The outstanding performance of the FaNTA realization can be quantified by introducing a new model for the bimodal separation index. Since FaNTA is applicable to all types of nano-objects down to sub-20 nm diameters, the method will improve the precision standard of mono- and polydisperse nanoparticle samples such as nano-plastics or extracellular vesicles.

High-speed tracking of nano-objects is a gateway to understanding biological processes at the nanoscale. Here we will present our results on tracking single or ensembles of nano-objects inside optofluidic fibers via elastic light scattering. The nano-objects diffuse inside a channel of a microstructured fiber and the light scattered by the nano-object is detected transversely via a microscope. We will present the fundamentals of this approach and focus on selected results including retrieval of the full 3D trajectory of a diffusing nano-sphere, the simultaneous detection of hundreds of nano-objects in hollow core anti-resonant fibers and first results on inactivated SARS-CoV-2.

Coupling of light into optical fibers is important for many applications, while for commonly used step-index optical fibers it massively drops for oblique incident angles

High-speed tracking of nano-objects is a gateway to understanding biological processes at the nanoscale. Here we will present our results on tracking single or ensembles of nano-objects inside optofluidic fibers via elastic light scattering. The nano-objects diffuse inside a channel of a microstructured fiber and the light scattered by the nano-object is detected transversely via a microscope. We will present the fundamentals of this approach and focus on selected results including retrieval of the full 3D trajectory of a diffusing nano-sphere, the simultaneous detection of hundreds of nano-objects in hollow core anti-resonant fibers and first results on inactivated SARS-CoV-2.

We tracked unlabeled SARS-CoV-2 viruses inside a hollow core optical fiber by elastic light scattering. The simultaneous confinement of particles and light leads to intense scattering, long trajectories and consequently a precise nanoparticle tracking analysis.

We demonstrate experimentally and in simulation record-high efficiencies for coupling of light into step-index fibers a t a lmost g razing i ncidence v ia t he i nclusion of axial-symmetric dielectric nanostructures, realized by electron-beam-lithography, onto the fiber facet.

The light cage is a 3D nanoprinted hollow-core waveguide which can be used as an integrated light-matter interaction platform. Here we present the fiber-connected version of light cage and demonstrate ammonia gas sensing using tunable diode laser absorption spectroscopy.

Experimental viscosity data for (GeSe2)x(Sb2Se3)100-x melts (x = 50, 60 and 70), obtained by deploying the pressure-assisted melt filling technique (PAMFT), are presented. These data were combined with previously published literature data and fitted over a broad temperature range including glass, undercooled melt, and melt regions by the Mauro–Yue–Ellison–Gupta–Allan (MYEGA) equation. A detailed analysis of different fragility concepts for the studied glass-forming system as well as for other well-known chalcogenide glass formers is presented. On the basis of this extensive analysis, a simple procedure for carrying out viscosity data extrapolation was developed, and the validity of this procedure is discussed.

We experimentally demonstrate a hybrid plasmonic fiber with tuneable Eigenmode interactions near the exceptional point, via near-infrared transmission experiments. We present a design at visible wavelengths, extending design opportunities for tuneable non-Hermitian waveguide systems.

We experimentally observe an effective $\mathcal{P}\mathcal{T}$-phase transition through the exceptional point in a hybrid plasmonic-dielectric waveguide system. Transmission experiments reveal fundamental changes in the underlying eigenmode interactions as the environmental refractive index is tuned, which can be unambiguously attributed to a crossing through the plasmonic exceptional point. These results extend the design opportunities for tunable non-Hermitian physics to plasmonic systems.

We experimentally demonstrate a hybrid plasmonic fiber with tuneable Eigenmode interactions near the exceptional point. We experimentally observe a transition through the exceptional point in a fiber-plasmonic system: transmission experiments reveal fundamental changes in the underlying Eigenmode interactions as the environmental refractive index is tuned due to a crossing through the plasmonic exceptional point. These results extend the design opportunities for tunable non-Hermitian physics to plasmonic waveguide systems.

Magnetooptical (MO) glasses and, in particular, Faraday rotators are becoming key components in lasers and optical information processing, light switching, coding, filtering, and sensing. The common design of such Faraday rotator materials follows a simple path: high Faraday rotation is achieved by maximizing the concentration of paramagnetic ion species in a given matrix material. However, this approach has reached its limits in terms of MO performance; hence, glass‐based materials can presently not be used efficiently in thin film MO applications. Here, a novel strategy which overcomes this limitation is demonstrated. Using vitreous films of xFeO·(100 − x)SiO2, unusually large Faraday rotation has been obtained, beating the performance of any other glassy material by up to two orders of magnitude. It is shown that this is due to the incorporation of small, ferromagnetic clusters of atomic iron which are generated in line during laser deposition and rapid condensation of the thin film, generating superparamagnetism. The size of these clusters underbids the present record of metallic Fe incorporation and experimental verification in glass matrices.

We describe a novel, fully symmetrical deposition method, based on a sputtering technique and use of a gold ring target for deposition of a gold layer uniform around the taper waist. With such a circular symmetric coating, the plasmon resonance effect in the fiber taper becomes completely independent of the polarization of the illuminating light. We have measured the complex refractive index of such sputtered gold layers. On this basis, model calculations have been performed to describe the plasmon resonance as a function of taper waist diameter, gold layer thickness, analyte interaction length, and analyte refractive index. Optimized parameters especially for measurement in aqueous solutions are derived from these theoretical calculations. Experimental results are shown to be in good agreement with the theoretical analysis.

Due to the ongoing improvement in nanostructuring technology, ultrathin metallic nanofilms have recently gained substantial attention in plasmonics, e.g. as building blocks of metasurfaces. Typically, noble metals such as silver or gold are the materials of choice, due to their excellent optical properties, however they also possess some intrinsic disadvantages. Here, we introduce niobium nanofilms (~10 nm thickness) as an alternate plasmonic platform. We demonstrate functionality by depositing a niobium nanofilm on a plasmonic fiber taper and observe a dielectric-loaded niobium surface-plasmon excitation for the first time, with a modal attenuation of only 3–4 dB/mm in aqueous environment and a refractive index sensitivity up to 15 μm/RIU if the analyte index exceeds 1.42. We show that the niobium nanofilm possesses bulk optical properties, is continuous, homogenous and inert against any environmental influence, thus possessing several superior properties compared to noble metal nanofilms. These results demonstrate that ultrathin niobium nanofilms can serve as a new platform for biomedical diagnostics, superconducting photonics, ultrathin metasurfaces or new types of optoelectronic devices.

Faseroptische Sensoren besitzen aufgrund ihrer optischen Wirkprinzipien Eigenschaften (z.B. Unempfindlichkeit gegenüber elektromagnetischen Störfeldern und Explosionseigensicherheit), die sie gegenüber konventionellen elektrischen Sensoren auszeichnen. In diesem Beitrag wird ein faseroptischer Drucksensor nach dem Fabry-Pérot-Prinzip beschrieben, welcher zu einer Familie streckenneutraler faseroptischer Sensoren mit spektraloptischer Auswertung gehört.

We discuss a fiber-integrated refractive index sensor with strongly improved detection performance. The resonator has been implemented by means of focused-ion beam milling of a step index fiber and shows a sensitivity of about 1.15µm/RIU. Coating the resonator walls led to a strongly improved mirror reflectivity by a factor of about 26. Design rules for device optimization and a detailed mathematical analysis are discussed, revealing that the sensor operates as an optimized Fabry-Perot resonator. We also show that the performance of such kind of Fabry-Perot sensors is, in general, limited by the detection limit function – a quantity depending on the cavitiy’s finesse and on the measurement capabilities used.

We present a novel design for a compact flow-through fluorescence detector for flow analyses applications and prove its functionality in the experiment. The detector operates by detecting the diffusely emitted fluorescence in a glass capillary, which is a measure for the concentration of the analyte to be detected. The fluorescence is excited via an axially coupled fibre providing LED light and is collected by a photodiode. As model analyte we used dissolved reactive phosphate. The determination of the phosphate concentration is based on the reaction of molybdate to phosphomolybdate, which quenches the fluorescence of Rhodamine 6G. The experiments rely on a reversed flow injection analysis system especially designed for decoupling the analytical setup from environmental pressure for in situ applications. By combining the optics part and the fluidic setup a measuring range of 0-40 µg L(-1) PO4-P with detection limits of 0.22 µg L(-1) PO4-P (7 nmol L(-1)) for water and of 0.45 µg L(-1) PO4-P (14.5 nmol L(-1)) for seawater have been obtained. Our novel system has a sampling frequency of up to 300 samples per hour and achieves a repeatability between 0.6% (RSD) for the blank value signal (n=15) and 4.6% (RSD) for a phosphate concentration of 20.8 µg L(-1) PO4-P (n=15).

We reveal the potential of step-index fibers consisting of a metaphosphate glass core and a silica cladding as an ultrafast octave-spanning supercontinuum source. The hybrid waveguide was fabricated by pressure-assisted melt filling and possesses a sophisticated dispersion behavior with two zero-dispersion points in the proximity of the Erbium laser bands. The fiber generates an octave-spanning supercontinuum from 0.7 to 2.4 μm if pumped at 1.56 μm with 30 fs pulses and energies as low as 300 pJ. Numerical simulations reveal soliton fission and double dispersive wave generation as the dominant broadening effect. This study highlights phosphate glasses as a promising new candidate for the next generation of broadband photonic devices, as they allow for high rare earth-doping levels and dispersion posttuning via plasmonic nanoparticle growth.

Phosphate glasses represent promising candidates for next-generation photonic devices due to their unique characteristics, such as vastly tunable optical properties, and high rare earth solubility. Here we show that silver metaphosphate wires with bulk optical properties and diameters as small as 2 µm can be integrated into silica fibers using pressure-assisted melt filling. By analyzing two types of hybrid metaphosphate-silica fibers, we show that the filled metaphosphate glass has only negligible higher attenuation and a refractive index that is identical to the bulk material. The presented results pave the way towards new fiber-type optical devices relying on metaphosphate glasses, which are promising materials for applications in nonlinear optics, sensing and spectral filtering.

Optical resonance coupling between a side-polished fiber and thin film waveguides has been investigated in the presence of biochemical adsorbates. The shift of the resonance wavelengths was found to be highly sensitive to the capture of target DNA recognition elements with Au nanoparticle markers, allowing for a sensitivity limit of 10 particles on the side-polished fiber core area (2000 μm²) during on-line measurements using a polychromator spectrometer.

Liquid core wave guides (LCW) are particularly suited as flow-through cells for highly sensitive spectral analysis of small liquid sample volumes as the light propagation is constrained to the liquid core. We report on LCW formed by inside coating of glass capillaries with Teflon® AF 1600 (n § 1.31). The wave guiding losses are between 0.2 and 0.3 dB/cm. On the base of fiber-coupled LCW flow-through cells both, a spectrophotometer and a fluorescence detector have been developed and tested for in-situ water analysis, especially for nitrate and phosphate detection in sea water. Keywords: liquid core wave guides, fiber-coupled flow cells, water analysis 1. INTRODUCTION Nutrients as nitrate, phosphate, and ammonium are essential substances for the metabolism of plants. Due to the intensification of agriculture, the nutrient contents, especia lly in natural water have increased. The presence of nutrients in drinking water reservoirs, lakes, rivers and in the sea infl uences the quality of water and has serious consequences for animal and human health. Therefore, continuous water monitori ng is essential for the evaluation of the water quality. The usual practice is water sampling followed by sample storage, handling and analysis in a laboratory. This procedure is costly and does not provide large data sets of spatial distribution or temporal evolution of dissolved nutrients. To overcome these problems automatic flow analysis (FA) meth ods [1] and equipments are in development. Requirements for such an automated analyzer for in-s itu measurements are high sampling rates, small sample volumes, low reagent and energy consumption, and last but not least, robustness and reliability. Furthermore, various applications, such as marine applications, require lowest detection limits down to the ppb range. The analysis of nutrients in aquatic systems by FA methods is commonly based on the formation of colored chemical reaction products and their photometric or fluorometric detection [2]. Additionally, nitrate contents can be determined directly by UV spectrophotometry without chemical pretreatment [3]. High sensitivity photometric detection requires long optical path length. In any case, FA equipments with optical detection need flow-through cells for low sample volumes. In this paper we report on developments of optical flow-through cells and equipments for nutrient measurements in water with low detection limits both for in-situ and for laboratory use.

Magnetooptical (MO) glasses and, in particular, Faraday rotators are becoming key components in lasers and optical information processing, light switching, coding, filtering, and sensing. The common design of such Faraday rotator materials follows a simple path: high Faraday rotation is achieved by maximizing the concentration of paramagnetic ion species in a given matrix material. However, this approach has reached its limits in terms of MO performance; hence, glass���based materials can presently not be used efficiently in thin film MO applications. Here, a novel strategy which overcomes this limitation is demonstrated. Using vitreous films of xFeO��(100 ��� x)SiO2, unusually large Faraday rotation has been obtained, beating the performance of any other glassy material by up to two orders of magnitude. It is shown that this is due to the incorporation of small, ferromagnetic clusters of atomic iron which are generated in line during laser deposition and rapid condensation of the thin film, generating superparamagnetism. The size of these clusters underbids the present record of metallic Fe incorporation and experimental verification in glass matrices.