Kerstin Schröder

Functionalization of Microstructured Optical Fibers by Internal Nanoparticle Mono-Layers for Plasmonic Biosensor Applications

For fully integrated next-generation plasmonic devices, microstructured optical fibers (MOFs) represent a promising platform technology. This paper describes the use of a dynamic technique to demonstrate the wet chemical deposition of gold and silver nanoparticles (NPs) within MOFs. The plasmonic structures were realized on the internal capillary walls of a three-hole suspended core fiber. Electron micrographs, taken of the inside of the fiber holes, confirm the even distribution of the NP in the MOF over a length of up to 6 m. Accordingly, this procedure is highly productive and makes the resulting MOF-based sensors potentially (very) cost efficient. In proof-of-principle experiments with liquids of different refractive indices, the dependence of the localized surface plasmon resonance (LSPR) on the surroundings was confirmed. Comparing Raman spectra of MOFs with and without NP layers, each one filled with crystal violet, a significant signal enhancement demonstrates the usability of such functionalized MOFs for surface-enhanced Raman spectroscopy (SERS) experiments.

ORMOCER Coated Fiber-Optic Bragg Grating Sensors at Cryogenic Temperatures

ORMOCER coated Fiber-Bragg-Gratings (FBGs) were investigated at cryogenic temperatures. Below the Bragg wavelength of uncoated FBG is nearly independent on temperature. ORMOCER coated FBG are temperature dependent over the whole temperature range investigated from 10 to 300 K. For 50-300 K, the ORMOCER coating contributes to an additional linear temperature shift of the Bragg wavelength of 2.4 pm/K. Below 40 K the temperature dependence decreases to 1.0 pm/K. ORMOCER coated FBGs can be used as sensor at cryogenic temperatures.

Smart current collector—fibre optic hit detection system for improved security on railway tracks

In a deregulated EU railway market, monitoring the vehicle and infrastructure interfaces is mandatory for the enhanced availability of operation and for reducing costs. Therefore, infrastructure managers need monitoring tools on overhead contact lines (OCLs). We know from earlier investigations that a measurement of contact forces alone is not sufficient (Schr?der et?al 2013 Opt. Lasers Eng. 51 172?9). In this study, we introduce a system which is fast enough to detect short disturbances and which can be used with regular trains. It is based on fibre optic sensors integrated with conventional current collectors (CCs). The system is designed to monitor hard and soft hits on the CC in horizontal (driving) and vertical (contact) direction. It was systematically tested in the laboratory as well as in test runs on commercial railways in several countries. With its help, a variety of minor as well as serious defects have been discovered and repaired at the CC?OCL interface.

Monolayers of different metal nanoparticles in microstructured optical fibers with multiplex plasmonic properties

Microstructured optical fibers (MOFs) show plasmonic properties after deposition of metal nanoparticles on the surface of their capillaries. A method of enhancing the functionality of such fibers by immobilizing different nanoparticles in the different capillaries of an MOF is described. Silver and gold nanoparticles show well-separated localized surface plasmon resonances (LSPRs). Measurements confirm calculations, according to which both resonance wavelengths shift with changes in the refractive index of the nanoparticles’ immediate environment. Such modified MOFs can be used in LSPR sensing; they may also be used in multiplex detection of bio-analytes, in particular.

Fiber Bragg grating sensor system for operational load monitoring of wind turbine blades

A fiber optic Bragg grating sensor system has been installed in the blades of a wind turbine and was successfully tested for several years. We report the requirements, system design and construction parameters of a sensor system for continuous on-line monitoring of bending loads of the rotor blades, and provide characteristic examples of monitoring results.

Characterization of fiber Bragg grating-based sensor array for high resolution manometry

The combination of fiber Bragg grating arrays integrated in a soft plastic tube is promising for high resolution manometry (HRM) where pressure measurements are done with high spatial resolution. The application as a medical device and in vivo experiments have to be anticipated by characterization with a measurement setup that simulates natural conditions. Good results are achieved with a pressure chamber which applies a well-defined pressure with a soft tubular membrane. It is shown that the proposed catheter design reaches accuracies down to 1 mbar and 1 cm.

Fiber optic Bragg grating sensors at cryogenic temperatures

Advantages of optical fiber Bragg grating sensors at low temperatures, are electrical isolation, low electro-magnetic interference, low thermal conductivity to a large number of multiplexed sensors. They show negligible thermo-optic and magnetooptic effects in cryogenic environment. These properties make them attractive for temperature surveillance and structural health monitoring of cryogenic systems, or for the testing of material properties and system components at low temperatures.

Microstructured optical fiber with homogeneous monolayer of plasmonic nanoparticles for bioanalysis

Microstructured optical fibers (MOFs) represent a promising platform technology for fully integrated, next generation plasmonic devices. This paper details the use of a dynamic chemical deposition technique to demonstrate the wet chemical deposition of gold and silver nanoparticles (NP) within MOFs with longitudinal, homogenously-distributed particle densities. The plasmonic structures were realized on the internal capillary walls of a three-hole suspended core fiber. The population density of the NP on the surface, which directly influences the usable / necessary sensor length, can be tailored via the controlled pre-treatment of the fiber. With the proposed procedure we can coat several meters of fiber and, afterwards, cut the fiber into the desired lengths. Accordingly, this procedure is highly productive and makes the resulting MOF-based sensors potentially very cheap. Electron microscope micrographs, taken of the inside of the fiber holes, confirm the even distribution of the NP. A transversal through-light setup was used for the non-destructive layer characterization. In proof-of-principle experiments with liquids of different refractive indices, the LSPR dependence on the surroundings was confirmed and compared with Mie-theory based calculations.

Plasmonic nanoparticles for optical biosensing

Metal nanoparticles exhibit a large potential for the development of innovative and cost-effective sensing devices. They fulfill key requirements for biosensors such as the potential for miniaturization as well as for high parallelization, and they are compatible with the molecular world for the required biofunctionalization approaches. Their optical properties based on the localized surface plasmon resonance (LSPR) are well adjustable from the UV- to the infrared spectral range using chemical synthesis. Due to the strong influence of the surrounding dielectrics on the resonant properties these particles offer a high potential for sensing of minimal changes in the surrounding media. Additionally, plasmon nanoparticles can induce a local field-enhancement and so a signal amplification such as for fluorescence or Raman-spectroscopy. In general, plasmon nanoparticles are well suited as label or as transducer for different optical detection techniques. We will give an overview about recent developments in this field, and will present different sensing strategies at single particle or ensemble level and based on planar or fiber-based systems aiming for ultrasensitive point-of care applications in bioanalytics.

Multiplexed localized surface plasmon resonance sensing with suspended core fibers

Sensors based on the localized surface plasmon resonance (LSPR) effect are known as sensitive methods for refractive index measurements or for detection of specific binding reactions in biosensing due to a variation in layer thickness. Fiber based arrangements are able to perform such measurements with very small analyte volumina. A generalization of this concept for a multiplexed measurement of different biomolecules in a single fiber could be an attractive approach. We discuss the possibility of selectively sensitizing the inner surfaces of a suspended core fiber with two different metallic nanoparticle types in monolayers for such multiplexed measurements.