Functionalization of Microstructured Optical Fibers by ... - IEEE Xplore

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Functionalization of Microstructured Optical Fibers by Internal Nanoparticle Mono-Layers for Plasmonic Biosensor Applications Kerstin Schröder, Andrea Csáki, Anka Schwuchow, Franka Jahn, Katharina Strelau, Ines Latka, Thomas Henkel, Daniell Malsch, Kay Schuster, Karina Weber, Thomas Schneider, Robert Möller, and Wolfgang Fritzsche

Abstract—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. Index Terms—Localized surface plasmon resonance (LSPR), metal nanoparticle (NP), microstructured optical fiber (MOF), surface-enhanced raman spectroscopy (SERS).

I. INTRODUCTION

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HE DEVELOPMENT of the next generation of photonicplasmonic devices has aroused interest in fibers which incorporate metallic thin films or nanoparticles (NPs). Localized surface plasmons (LSP) are generated using NPs. With LSP a fixed and determined state of polarization is not needed (when Manuscript received November 12, 2010; revised April 11, 2011; accepted April 11, 2011. Date of publication May 10, 2011; date of current version December 01, 2011. This work was supported in part by the Executive Committee of the IPHT Jena, and is a result of the cooperation of different groups in the Institute of Photonic Technology (IPHT), Jena, Germany. An earlier version of this paper was presented at EWOFS 2010 in Porto, Portugal, and was published in its proceedings. The associate editor coordinating the review of this paper and approving it for publication was Prof. Jose Santos. K. Schröder is with the Department of Fiber Sensor Systems, Institute of Photonic Technology (IPHT) Jena, 07745 Jena, Germany (e-mail: [email protected]). A. Csáki, A. Schwuchow, F. Jahn, K. Strelau, I. Latka, T. Henkel, D. Malsch, K. Schuster, K. Weber, T. Schneider, R. Möller, and W. Fritzsche are with the Institute of Photonic Technology (IPHT) Jena, 07702 Jena, Germany (e-mail: [email protected]; [email protected]; [email protected];; [email protected]; ines.latka@ ipht-jena.de; [email protected]; [email protected]; [email protected]; [email protected]; thomas.schneider@ ipht-jena.de; [email protected]; [email protected]). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JSEN.2011.2144580

NPs are circular or noncircular NPs are arranged in a nonregular order), in contrast to surface plasmon resonance [2]. The sensitivity of the plasmon excitation to changes in the refractive index (RI) of the surrounding dielectric renders the photonic-plasmonic devices excellent candidates for optical sensing. All-fiber devices offer a number of advantages over conventional planar plasmonic structures in that they are cheap, compact, robust, flexible, and compatible with existing fiber infrastructures. In this paper, we present the experimental realization of NP-based plasmonic structures on the internal capillary walls of MOFs. It has been proposed that the evanescent field could be used for the sensing of gases and liquids within the holes of the fiber [3]. The deposition of NP inside the fiber voids has the potential to explore new directions in micro/nanomaterials technology. Recently, high-pressure chemical deposition techniques or static procedures, respectively, have been developed for the inclusion of a wide range of technologically important materials, such as silicon and germanium, within MOF capillaries. We propose a dynamic low pressure deposition of metal NP, in which NP are chemically attached in a self-assembled monolayer (SAM) to the inner surfaces of the MOF. With this nanoparticle layer deposition (NLD) method, an even deposition of NP is possible without the threat of damaging the thin struts of the fiber. Possible fields of applications include surface-enhanced raman spectroscopy (SERS) [4] and surface-enhanced fluorescence, which use the field enhancement near the particle surface [5], refractive index measurement, biomolecule detection [6], or THz waveguiding [7], respectively. Metal NP are under investigation in LSPR sensors as transducers for signal transfers. The effect is based on the spectral shift of the localized plasmon resonance which occurs when the analyte binds to the particle surface. In [8], the performances of LSPR sensing and surface plasmon resonance (SPR) sensing were compared for a special sensing example. MOFs which are modified with gold NPs could also be interesting for a fiber-based analysis of samples via SERS. This analytical method enables the enhancement of the intrinsically weak Raman signal since the analyte molecules interact with a nanostructured metal surface. Commonly used metals for these so-called SERS substrates are the coin metals, gold, and silver. When using appropriate SERS substrates an increase of sensitivity by several orders of magnitude and even single molecule detection can be achieved [9]. Besides the enhancement effect, the application of a vibrational spectroscopic method enables

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SCHRÖDER et al.: FUNCTIONALIZATION OF MOFS BY INTERNAL NP MONO-LAYERS FOR PLASMONIC BIOSENSOR APPLICATIONS

Fig. 1. (a) Micrograph of the end face of the MOF with NP layer. (b) NP modified fibers appear colored (upper fiber with gold NP) in comparison to unmodified fibers (lower fiber).

the detection and identification of nearly every analyte due to the highly specific Raman spectra of each molecule, the so-called molecular fingerprint. In a proof-of-principle experiment, the suitability of the fabricated MOF for SERS measurements was demonstrated by detecting the standard analyte molecule crystal violet. II. SAMPLE PREPARATION The MOFs we employed were prepared in-house by the so-called “stack-and-draw” technology from preforms of high purity silica glass. For the first filling experiments, we used a three-holed suspended core fiber [Fig. 1(a)] with a core , hole diameters of 30 (radial), and an diameter of 3.2 . This fiber type was chosen for our outer diameter of 125 project because it was readily available and easy to handle. Other fiber concepts predict better signal-to-noise ratio for the ) sensor evaluation. Big hole diameters (no smaller than 20 allow easy handling during fiber filling, so that long fiber lengths (about 6 meters) can be filled with moderate pressure (approximately 8 bar). Originally, the cleaved MOF was fixed to the feeding tubes (PVC) via a conventional adapter. A peristaltic pump, adjusted , was used for the delivery of the liquids. to a rate of 1 With this delivery rate a complete liquid exchange in a 40 cm long piece of the described fiber type requires about 15 min. Distilled water was fed through the fiber for 20 min to remove possibly present residuals originating from fiber fabrication. After cleaning and surface activation steps with a mixture of different acids, a silane solution (APTES) was fed through for surface of at least 1 h. The silane chemically binds to the the fiber and provides the coupling sites for the NP (for details see [10]–[12]). By using a well chosen mixture of bonding and nonbonding silanes for the NLD process, we should be able to adjust the particle density on the capillary surfaces. In the experiments described here, we used a very high population density. After a final washing step, the fiber was prepared to be filled with NP. Different NP, prepared via the Turkevich/Frens method method [13], [14], were tried due to their deposition behavior, even though, only one particle type in one fiber sample. Triangles, spheres or nanorods, respectively, were used with sizes ranging from 12 to 120 nm. Usually, the NP solution, which must be pumped through the MOF, has a specific color. For instance, light red for gold NP and blue for silver triangles

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Fig. 2. Photograph of a microfludic chip (16 mm 12.5 mm) with fiber channel with a glued fiber and five fluidic channels. The adapters for fluidic coupling are not attached yet.

edge length. A “spent” solution is impoverished with of NP and loses its color. With the help of this effect an easy control of the process is possible: as long as some binding sites are unoccupied, the solution which leaves the fiber at its end is clear. By the time all available binding sites are occupied, the solution becomes colored because of the remaining NP in it. This filling process takes about 30–60 min for fiber lengths of approximately 40 cm. After a cleaning and drying process the fiber appears colored, with the brightness depending on the NP density [see Fig. 1(b)]. A major improvement in the preparation efficiency was the utilization of a microfluidic chip [15] for fiber–fluidic coupling. This chip was specifically designed for this application (Fig. 2). Within the chip we created a section for fiber fixation (via gluing) and five different fluid ports which can be connected with pressure stable adapters. The chip device was prepared with wet etching technology and anodic bonding of two glass substrates using a bond support layer (details are given in [16]). In brief, channels were etched in two glass substrates using Hydrofluoric acid. Closed channels were constructed by bonding the two glass substrates together using an anodic bonding process mediated by a silicon bond support layer. The channel diameter is adapted to the fiber’s outer diameter. A V-slot was incorporated to ease the mounting of the MOF into the fiber channel from the chips edge. The five different ports connected to the fiber channel improve the handling during the filling process because they make tube cleaning and tube exchanging unnecessary. In addition, as a result of the smaller and shorter delivery tubes, the necessary amount of NP solution decreases significantly. With the coupling chip, the fluidic–fiber connection can be made leakproof for pressures of up to 10 bar, allowing the NLD of much longer fibers in one procedure. A NP modified fiber approximately 6 meters in length was the longest tested in our experimentation. This can be cut into desired lengths for sensors afterwards. Accordingly, this procedure is highly productive and makes the resulting MOF-based sensors potentially very cheap. As shown in Fig. 1, the easiest way to confirm a successful NP attachment on the inner surfaces is achieved by optical inspection, e.g., with a light-optical microscope, either from the end face or from the side. To check the NP density and layer uniformity, scanning electron micrographs (SEM Zeiss DSM 960)

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Fig. 3. SEM-pictures (45 angled view) from the two fiber ends. (a) Filling side. (b) Exit side of a MOF modified with 30 nm Ø gold spheres layer.

were taken of different sections of the modified fibers (Fig. 3). In preparation for the scans these fibers were cut into pieces with a fiber optic cleaver. No images of the NP layer could be taken of the top view as the only access to it was from the fiber end face. Fig. 3(a) and (b) show images of a suspended core fiber with a 30 nm gold sphere layer. The images are taken from opposite ends of a 30 cm fiber, from an angled position (45 ), and demonstrate that the population density is nearly constant over for the entire fiber length, namely 443 and 459 these two pictures. In addition, good homogeneity of the NP layer is documented; there were no large areas without NP and only a few clusters were detected. In comparison to other tested NP layer deposition techniques, with the NLD the NP density is also homogeneous along the hole’s diameter, independent of the local curvature of the capillary channel cross section. III. MEASUREMENTS AND DISCUSSION To check the usability of the NP modified MOF, we carried out proof-of-principle measurements with our fiber samples. We checked that an extinction peak was achieved in the LSPR measurements and also that as the refractive index of the surrounding material was changed, this peak moved correspondingly. In order to determine if NP modified fibers could be used as the substrate in a SERS method, the fibers were filled with crystal violet and the Raman spectrum was analyzed. A. LSPR Characterization To use the NP layer as a transducer for refractive index change detections, like DNA analytics, a transmission spectrum or transmissions at some specially defined wavelengths have to be measured. From this transmission, we calculate the extinction spectrum:

This extinction spectrum included the wavelength dependent absorbing and scattering behavior of the NP solution or NP layer.

Fig. 4. Experimental setup for transversal transmission measurements.

Because of the expected high signal-to-noise ratio, layers ) were prepared. with high NP density ( 1) Measurement Setup: Accessing both light and measurand (e.g., fluids) via the same end of the MOF is a difficult problem. A possible method for characterizing the NP layer is to illuminate and collect the light transversally to the fiber axis (Fig. 4). With this approach both fiber ends are available for filling with the fluids to be tested. The fiber–fluidic coupling can be performed in the same way as for NLD. As a result of the high NP density there was enough NP–light interaction in the illuminated area to measure clearly visible extinction spectra (Fig. 5). An illumination and measurement along the fiber axis would suffer from the difficulties of strong attenuation with regard to the metallic NP, which is not limited to the resonance region, and to the demanding fiber alignment. A white light source or a Xenon lamp were used for transversal fiber illumination. The plasmonically modified MOF was positioned into the collimated beam of that source. Using a well matched collecting fiber the transmission spectra are lead into the spectrometer for analysis. This fiber was directly connected to a spectrometer (Instrument Systems Spectro 320–164 or homemade compact spectrometer MINOS, respectively [17]). A MOF without NP was used as the reference.

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Fig. 5. Extinction spectra of MOFs with internal NP layers of: Ag triangle with base length of about 50 and 100 nm and Au spheres with diameter 30 nm.

First, measurements with this setup were made on MOFs plasmonically modified with different types of NPs. In Fig. 5, typical extinction spectra for different Ag triangles and Au spheres are diagrammed. These spectra agree very well with those taken with the same NP in solution [18]. In some cases, a subsidiary peak appeared when the NP were bound onto a surface. This could be caused by surface effects [19], nonspherical size distribution of the NP, and/or dipole-dipole interaction between the particles in the plasmonic layers. All measurements presented in the following were made with 30 nm Ø Au spheres. 2) Results: To determine the sensitivity of the LSP resonance to RI changes, liquids with defined RI were injected into the MOF sample arranged in a similar setup as for the particle layer preparation. All measurements were taken on exactly the same place of the MOF and the collecting fiber, avoiding uncertainties from differing alignments. This seems to be the only way to guarantee reproducible spectra. Transmission spectra were taken [Fig. 6(a)] and after each liquid measurement the fiber was cleaned with water, dried, and a control spectrum was recorded. This procedure tested the complete removal of the liquids, as well as the stability of the bond of the NP to the silica surface. If needed, the cleaning procedure can be repeated but we found that no more than one additional cleaning was ever necessary. To determine the sensitivity, i.e., the wavelength shift of the LSP resonance versus refractive index shift, not only the main peak – which relates to the NP resonance itself, but also the second peak – which was observed only with surface bound NP, were investigated. At first, a baseline subtraction was achieved. Following the fitting of both peaks, their position is given over , the RI of the surrounding medium, in Fig. 6(b). For the first , roughly approximated peak, we got a sensitivity to 1.515, as a linear fit of the measured curve from ( ). The of second peak’s sensitivity was determined with the same approx. To assess these results, it is imation as necessary to take into account that the second peak is smaller and therefore, the peak position cannot be determined without higher inaccuracy than that of the first peak. To evaluate the sensitivity of the first peak, extinction cross sections for a single spherical NP in different surrounding ma-

Fig. 6. (a) Baseline subtracted extinction spectra for a MOF with internal NP layers of 30 nm Au spheres and filled with liquids of different RI. (b) Two maxima of these spectra over the prevailing RI.

terials were calculated. Details are discussed in a former publication [1]. The calculated RI sensitivity of is reproduced by our measurement. The sensitivity of the LSP resonance to the surrounding refractive index can be increased as it is dependent on the size, the shape, and the material of the NP. For example, when using core-shell-particles the sensitivity should reach [20]. These findings will be further values of investigated in upcoming experiments. The aforementioned measurements were performed after removal of the protective acrylate coating. As the removal of the coating is disadvantageous for the mechanical stability of the fiber, its influence on the transmission measurements was looked into. The coating material Acrylat DeSolite® 3471–3-14 has no absorption bands in the wavelength region of interest. Comparison of transmission spectra of coated and uncoated fibers (Fig. 7) revealed that the spectral position or the width of the resonance peak, respectively, were not affected. The measurement through the fiber coating opens the opportunity for a quality control of the whole fiber directly after NP deposition process.

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Fig. 7. Comparison of extinction spectra measured through the coating and through an uncoated MOF, both filled with air.

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Fig. 8. Measured spectra of a 100  crystal violet solution. While the Raman spectrum, measured in an unmodified fiber, shows only noise and no specific bands, the SERS spectrum, detected in a NP modified fiber, shows a spectrum with many specific bands.

B. Application as Fiber Optic SERS Sensor 1) Measurement Setup: The coating was removed from the fiber in preparation for the measurements. Subsequently, one fiber with NP coating and one fiber without NP coating were insolution of the standard analyte crystal cubated with a 100 violet. The SERS measurements were performed using a confocal Raman microscope system alpha300 R (WITec, Ulm, Germany) and a 514 nm argon ion laser served as the excitation source. The laser light was focused through a 20 microscope objective onto the prepared fiber, resulting in laser strength of approximately 1 mW on the sample. The 180 back-scattered light was detected with a CCD camera (1024 127 pixels) operating at 208 K. The integration time for each spectrum was 1 s. 2) Results: In the first test, the possibility of using the prepared MOF to detect an analyte via SERS was demonstrated. Therefore, a solution of crystal violet was pumped through a NP coated fiber followed by a SERS measurement. The results are shown in Fig. 8. To demonstrate the enhancement effect of the NP layers, a MOF without NPs was prepared and measured as well. In comparison to the modified fiber, no Raman spectrum of the analyte was detectable.

Fig. 9. (a) Microscopic and (b) Raman images of a part of the with 30 nm Au spheres coated MOF. (a) Microscopic image with the scanned area. (b) False color image of the scanned region. The bright areas display regions with a high SERS intensity of the 1368 cm-1 peak of the analyte molecule crystal violet.

For the application of SERS as an analytical tool an even distribution of SERS active areas across a SERS substrate is necessary. The uniform distribution of the NPs within the fiber was shown by SEM measurements. Due to this uniform distribution a homogeneous SERS signal was expected within the MOF. To investigate the distribution of the SERS signal, an image scan was analyzed. Within this area with a size of 136 118 16048 spectra of the analyte molecule crystal violet were measured. To visualize the distribution of the SERS signal, the char, a N-phenyl stretch vibraacteristic Raman mode at 1368 tion was taken and their integrated SERS intensity was plotted. The results are shown in Fig. 9. The false color image clearly shows the SERS active areas within the fiber where the NP coating is present. Within the silica glass material of the fiber, where no NPs were immobilized, no noteworthy SERS signals could be detected. These observations indicate that the Raman signal of the analyte molecule crystal violet is enhanced due to the proximity to the metal NPs within the fiber. Thus, the MOF with NP layers fiber can be used as substrate for SERS experiments. An exact enhancement factor was not calculated yet because improvements in the measurement setup and sensor design are still under investigation. IV. SUMMARY Self assembled monolayer (SAM) techniques were used for the deposition of metal NPs into the channels of the microstructured optical fibers. In our first experiments, a suspended core fiber with three channels was used. SAM techniques are very flexible concerning the material, shape and the size of the employed NPs, which offers the possibility of tailoring the deposited layer for the individual sensor applications. An adapted multichannel microfluidic chip for the consecutive steps of the coating procedure ensures a reproducible, cost-effective, and contamination-free NP deposition. Optical inspection as well as electron microscopic evaluation confirmed the even deposition on the inner walls and constant population density over the fiber length.

SCHRÖDER et al.: FUNCTIONALIZATION OF MOFS BY INTERNAL NP MONO-LAYERS FOR PLASMONIC BIOSENSOR APPLICATIONS

The NLD technology offer the opportunity to design a sensor specifically for an intended application. In an easy to use transversal measurement setup which separates the light from the analyte “path,” the sensitivity of the LSPR peak and the subsidiary peak to the refractive index of the surrounding medium was measured and the correlation with simulations confirmed. The promising experiments with regard to a possible application as fiber-optic SERS sensor were performed, using crystal violet as model substance. REFERENCES [1] K. Schröder, A. Csaki, I. Latka, T. Henkel, D. Malsch, K. Schuster, T. Schneider, and D. Zopf, “Microstructured optical fiber with homogeneous monolayer of plasmonic nanoparticles for bioanalysis,” in Proc. EWOFS 2010, SPIE, 2010, vol. 7653 1B. [2] A. Hassani and M. Skorobogatiy, “Design of the microstructured optical fiber-based surface plasmon resonance sensors with enhanced microfluidics,” Opt. Exp., vol. 14, pp. 11616–11621, 2006. [3] T. M. Monro, D. J. Richardson, and P. J. Bennett, “Developing holey fibers for evanescent field devices,” Electron. Lett., vol. 35, no. 14, pp. 1188–1189, 1999. [4] A. Amezcua-Correa, J. Yang, C. E. Finlayson, A. C. Peacock, J. R. Hayes, P. J. A. Sazio, J. J. Baumberg, and S. M. Howdle, “Surface enhanced Raman scattering using microstructured optical fiber substrates,” Adv. Funct. Mater., vol. 17, pp. 2024–2030, 2007. [5] H. Szmacinski, K. Ray, and J. R. Lakowicz, “Metal-enhanced fluorescence of tryptophan residues in proteins: Application toward label-free bioassays,” Analy. Biochem., vol. 385, no. 2, pp. 358–364, 2009. [6] S. F. Cheng and L. K. Chau, “Colloidal gold-modified optical fiber for chemical and biochemical sensing,” Analy. Chem., vol. 75, pp. 16–21, 2003. [7] J. A. Harrington, R. George, P. Pedersen, and E. Mueller, “Hollow polycarbonate waveguides with inner Cu coatings for delivery of terahertz radiation,” Opt. Exp., vol. 12, no. 21, pp. 5263–5268, 2004. [8] M. Svedendahl, S. Chen, A. Dmitiev, and M. Käll, “Refractic sensing using propagating versus localized surface plasmons: A drect comparison,” Nano Lett., vol. 9, no. 12, pp. 4428–4433. [9] K. Hering, D. Cialla, K. Ackermann, T. Dörfer, R. Möller, H. Schneidewind, R. Mattheis, W. Fritzsche, P. Rösch, and J. Popp, “SERS: A versatile tool in chemical and biochemical diagnostics,” Anal. Bioanal. Chem., vol. 390, pp. 113–124, 2008. [10] A. Steinbrück, A. Csaki, K. Ritter, M. Leich, J. M. Köhler, and W. Fritzsche, “Gold-silver and silver-silver nanoparticle constructs based on DNA hybridization of thiol- and amino-functionalized oligonucleotides,” J. Biophotonics, vol. 1, pp. 104–113, 2008. [11] R. R. Bhat, D. A. Fischer, and J. Genzer, “Fabricating planar nanoparticle assemblies with number density gradients,” Langmuir, vol. 18, pp. 5640–5644, 2002. [12] Y. Fang and J. H. Hoh, “Surface-directed DNA condensation in the absence of soluble multivalent cations,” Nucleic Acids Res., vol. 26, no. 2, pp. 588–93, 1998. [13] J. Turkevich, P. C. Stevenson, and J. Hillier, “A study of the nucleation and growth processes in the synthesis of colloidal gold,” Discuss. Faraday. Soc., vol. 11, pp. 55–57, 1951. [14] G. Frens, “Controlled nucleation for the regulation of the particle size in monodisperse gold suspensions,” Nature (London), Phys. Sci., vol. 241, pp. 20–22, 1973. [15] IPHT Annular Report, , 2009. [Online]. Available: http://www.iphtjena.de/institut.html [16] T. Henkel, T. Bermig, M. Kielpinski, A. Grodrian, J. Metze, and J. Köhler, “Chip modules for generation and manipulation of fluid segments for micro serial flow processes,” Chem. Eng. J., vol. 101, p. 439, 2004. [17] G. Schwotzer, T. Wieduwilt, M. Giebel, R. Willsch, and W. Mueller, “Low-cost optical miniature spectrometers and their application in spectral-encoded optical fiber sensors,” in Proc. 4th Micro Techniques Thüringen, Tech. Digest, Erfurt, Germany, 2002. [18] A. Csaki, F. Jahn, I. Latka, T. Henkel, D. Malsch, T. Schneider, K. Schröder, K. Schuster, A. Schwuchow, R. Spittel, D. Zopf, and W. Fritzsche, “Nanoparticle layer deposition for plasmonic tuning of microstructured optical fibers,” Small, vol. 6, no. 22, pp. 2584–2589, Doi: 10.1002/smll.201001071. [19] W. Rechberger, “Optical properties of two interacting gold nanoparticles,” Opt. Commun., vol. 220, no. 1–3, pp. 137–141, 2003.

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[20] A. Csáki, S. Berg, N. Jahr, C. Leiterer, T. Schneider, A. Steinbrück, D. Zopf, and W. Fritzsche, “Plasmonic nanoparticles – noble material for sensoric applications,” in Gold Nanoparticles: Properties, Characterization and Fabrication, P. E. Chow, Ed. Hauppauge, NY: Nova Science Publishers, 2010, ch. 9.

Kerstin Schröder graduated as an Engineer in electro-technique/optical communication technique from Technische Hochschule Karlsruhe, Karlsruhe, Germany, in 1996 and a Dr. rer. nat. from the Physics Faculty, Friedrich-Schiller-Universität Jena, Jena, Germany, in 2001. She works at the Institute of Photonic Technology (IPHT) Jena, Germany, since 1996, in the development of fiber-optic sensing systems and their applications.

Andrea Csáki was born on October 26, 1967 in Nagykörös. She received the Ph.D. degree in nanotechnology/biology at the IPHT Jena/Friedrich-Schiller-Universität (biological pharmaceutical faculty) Jena, Jena, Germany, in 2003. Since 2003, she has been a Research Scientist at IPHT. Her first research aim was focused on the DNA-based molecular nanotechnology. Current works are focused on the molecular plasmonics and plasmonic bioanalytics.

Anka Schwuchow was born on April 18, 1970, in Jena, Germany. She received her diploma in communications engineering at the Technische Universität Dresden, in 1994. She works at the Institute of Photonic Technology (IPHT) Jena, Germany, as a Research Scientist, since 1994, active on characterization of rare earth doped and other special fibers and glass samples.

Franka Jahn was born on November 15, 1063 in Jena, Germany. She received the Diploma in mathematics and physics lectureship at the Friedrich-SchillerUniversität (mathematical faculty) Jena, Jena, Germany, in 1985. Since 1990, she has been a Technical Scientist at the Institute of Photonic Technology (IPHT), Jena, Germany. She is a specialist for TEM and SEM measurements and characterization of plasmonic structures.

Katharina Strelau, photograph and biography not available at the time of publication.

Ines Latka studied physics at the Technical University Ilmenau, Ilmenau, Germany, and the FriedrichSchiller University Jena, Jena, Germany. Currently, she is with the Institute of Photonic Technology (IPHT), Jena, Germany. After her degree she worked several years in the field of fiber-optic sensors for industrial applications, particularly with fiber Bragg gratings. In 2009, she joined the molecular imaging group at IPHT. Her new interests are focused on CARS applications as well as fiber-optic endoscopes, e.g., employing Raman scattering.

Thomas Henkel studied bio-organic chemistry at the Friedrich-Schiller-Universität Jena, Jena, Germany, and received the Dr. rer. nat. degree in 1994. Since 1997, he has been with the Institute of Photonic Technology (IPHT), Jena, active in microfluidics and lab-on-a-chip technology.

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Daniell Malsch, photograph and biography not available at the time of publication.

Kay Schuster, photograph and biography not available at the time of publication.

Karina Weber was born in 1979. She studied biotechnology at the University of Applied Sciences Jena, Jena, Germany (1997-2002). After her studies in chemical and process engineering at the Technical University, Clausthal-Zellerfeld (2002-2004), she received the Ph.D. degree from the University of Applied Sciences Jena in cooperation with the Technical University in Clausthal-Zellerfeld in 2006. Currently she is working at the Friedrich-Schiller-Univisität Jena. Her research is focused on the development and optimization of novel chip-based detection technologies for multiplex analysis of biomolecules and low molecular weight substances. Further she works on modification and functionalization of sensor surfaces.

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Thomas Schneider received the Degree in biology from the Friedrich-SchillerUniversity (FSU) Jena, Jena, Germany, in 2007. Currently, he is working towards the Ph.D. degree in nano-biophotonics at the Institute of Photonic Technology (IPHT), Jena, Germany. His research activities focus on the spectroscopic characterization of single metal nanoparticles and their application as optical biosensors.

Robert Möller, photograph and biography not available at the time of publication.

Wolfgang Fritzsche, photograph and biography not available at the time of publication.