Rozprawy doktorskie na temat „Grating Coupled Surface Plasmon Resonance”

The core of my research activity during the Ph.D. period has been the study and the development of Surface Plasmon Resonance (SPR) based sensors for the detection of molecules of biological and medical interest. In particular, between the different configurations allowing plasmon excitation, I have focused my research on the study of nanostructured gratings, which allow to achieve a higher sensitivity than the prism coupled sensors and to miniaturize the measurement system. First my activity focused on the development of an opto-electronic bench able to detect plasmonic signal and to transduce it into an electric one. The test bench must allow varying independently some parameters that are fundamental for plasmonic excitation, such as the incident angle of laser beam, the azimuthal angle between the scattering plane and the grating vector, and the incident light polarization. The light modulated by the grating is transduced into electrical current through a photodiodes array and then acquired by a parameters analyzer. I have realized a versatile bench in order to perform measurements of both reflectance, analyzing the light reflected from the grating, and transmittance. The use of a motorized rotation stage has automated the measurement and it is controlled by a custom National Instruments LabVIEW software: in this way only few initial steps must be manually performed. I have analyzed three types of gratings: - Gold sinusoidal grating, optimized for reflectance measurements in incident light polarization modulation, exploiting the sensitivity increase due to a non-zero azimuthal angle. This grating has been provided us by LaNN laboratory (Laboratory of research for Nanofabrication and Nanodevices) of National Council of Research (CNR) of Padova. The grating has been manufactured through lithography (by Laser Interference Lithography-LIL) of a photoresist deposited over a glass (or silicon wafer), nanostructure replica and thermal evaporation of the gold plasmonic layer. First I have analyzed the bare grating, and then I have measured bulk with different refractive indexes in order to estimate sensor sensitivity. Then I have measured if the sensor is able to detect biological molecules, first through tests of avidin detection, exploiting avidin-biotin binding, and then through tests of DNA detection, via complementary Peptide Nucleic Acid (PNA) immobilization. - Gold digital grating, that exploits light extraordinary transmission. This grating has been fabricated by LaNN laboratory of CNR of Padova through Electron Beam Lithography (EBL) technique, and it has been designed in order to realize a simple and compact detection system, since the only sensing parameter considered is incident light polarization. Grating ability to detect surface changes of refractive index has been evaluated by a functionalization process with dodecanethiol, that is a molecule composed of a chain of twelve carbon atoms that forms a layer of well- known thickness and refractive index. - Silver trapezoidal grating, developed thanks to the collaboration with the Spin-Off Next Step Engineering, that has involved me in the last months of my Ph.D.. In fact, I have participated in grating fabrication exploiting the industrial facilities of the Spin-Off, which allow producing high quantity of low-cost devices, suitable to be a disposable sensor. The manufacturing process consists of the development of a stamper obtained through interferential lithography, the replica molding of polymeric substrate and the metal layer deposition through sputtering. These gratings have been optimized for transmittance measurements and their response as a function of incident light and azimuthal angles has been analyzed. Measurements of bulk with different refractive indexes, in order to estimate sensor sensitivity, and then of grating functionalized with different lengths alkanethiols have been performed. All experimental data have been compared with simulations results. In fact the behavior of the gratings has been studied through different simulation methods. In particular the digital gold grating has been studied through Finite Element Method (FEM) implemented in COMSOL Multiphysics; the vector model has been applied for both sinusoidal gold gratings and trapezoidal silver ones. The latter grating has been also analyzed through Rigorous Coupled Wave Analysis (RCWA). As already mentioned, during the last period of my Ph.D., I have collaborated with Next Step Engineering to develop an innovative industrial process that allows creating both grating for plasmonic events detection and electronic/microfluidic hybrid devices within a single, well-established, production line. With this process I have manufactured all the custom devices I used for my experimental activity. Moreover, this industrial process is the object of an Italian patent that is now pending and I am one of the inventors. During my PhD I have also developed microfluidic devices through a particular technique of polymer etching, able to create clear-cut profiles without deforming the planar structure, and also through suitable changes of production process adopted by Next Step Engineering, previously mentioned. The former devices have been used with silver gratings for the measurements of bulk with different refractive indexes.
Il tema principale dell’attività di ricerca che ho svolto durante il mio periodo di Dottorato in Scienza e Tecnologia dell’Informazione è stato lo studio e lo sviluppo di sensori basati sull’effetto di risonanza plasmonica per la rilevazione di molecole di interesse medico e biologico. In particolare, tra le varie configurazioni che permettono l’eccitazione plasmonica, mi sono focalizzata sullo studio dei reticoli nanostrutturati, i quali permettono di raggiungere elevate sensibilità, se paragonati ai dispositivi accoppiati con prisma, e di miniaturizzare e integrare il sistema di misura come obiettivo nel lungo periodo. Inizialmente la mia attività si è concentrata sullo sviluppo di un banco opto-elettronico che permettesse di rilevare il segnale plasmonico e trasdurlo in un segnale elettrico. Il banco doveva essere in grado di variare indipendentemente alcuni parametri determinanti per l’eccitazione plasmonica, ossia l’angolo di incidenza del fascio laser, l’angolo azimutale tra il piano di scattering e il vettore del reticolo, e la polarizzazione della luce incidente. La luce modulata dal reticolo viene poi trasformata in corrente elettrica attraverso un array di fotodiodi, e quindi acquisita attraverso un analizzatore di parametri. Ho mirato a realizzare un banco molto versatile in modo da poter effettuare misure sia di riflettanza, andando ad analizzare la luce riflessa dal reticolo, sia di trasmittanza, analizzando la luce trasmessa dal campione. L’introduzione di uno stadio motorizzato ha permesso di rendere la misura più automatizzata e gestibile via software, attraverso un programma custom sviluppato in LabVIEW, e lasciando manuali solo pochi passaggi iniziali. Ho analizzato tre tipologie diverse di reticoli: - Reticolo d’oro con superficie sinusoidale, ottimizzato per effettuare misure in riflessione con modulazione della polarizzazione della luce incidente, sfruttando l’aumento di sensibilità derivante dall’angolo azimutale non nullo. Tale reticolo è stato fornito dal laboratorio LaNN (Laboratorio di ricerca per la Nanofabbricazione e i Nanodispositivi) del Consiglio Nazionale delle Ricerche (CNR) di Padova. Il reticolo è stato realizzato attraverso litografia interferenziale di uno strato di fotoresist deposto su un vetrino (o silicio), da cui è stato ricavato uno stampo che permette la replica della nano struttura; infine, attraverso un’evaporazione termica, è stato depositato uno strato d’oro. Inizialmente ho analizzato il reticolo in condizione “fresh”; successivamente ho effettuato misure di “bulk” con indici di rifrazione diversi, per poter stimare la sensibilità del sensore. Ho poi misurato la capacità del dispositivo nel rilevare molecole di interesse biologico, dapprima attraverso prove di rilevazione di avidina presente in una soluzione, sfruttando il legame avidina-biotina, poi con prove di rilevazione di singole catene di DNA, attraverso l’immobilizzazione sulla superficie della nanostruttra di acido peptidonucleico (PNA) complementare. - Reticolo d’oro digitale, ideato per sfruttare il fenomeno di trasmissione straordinaria della luce. Tale reticolo è stato realizzato dal laboratorio LaNN del CNR di Padova attraverso la tecnica di litografia a fascio di elettroni (Electron Beam Lithography-EBL) e nasce con l’obiettivo di creare un sistema di rilevazione estremamente semplice, poiché l’unico parametro di sensing, e quindi variabile, è la polarizzazione della luce incidente. La capacità del sistema di discriminare variazioni superficiali di indice di rifrazione è stata valutata funzionalizzando il reticolo con dodecanethiol, ossia una molecola composta da una catena di dodici atomi di carbonio in grado di formare uno strato di dimensioni e indice di rifrazione noti. - Reticolo trapezoidale in argento, nato dalla collaborazione con lo Spin-Off Next Step Engineering, che mi ha coinvolta nell’ultimo periodo di dottorato. Infatti, ho partecipato in prima persona alla realizzazione del sensore, sfruttando le facilities industriali a cui l’azienda ha accesso, permettendo di produrre dispositivi a basso costo e in elevate quantità, quindi adatti ad un utilizzo di tipo “usa e getta”. Il processo di fabbricazione prevede la realizzazione di uno stampo attraverso litografia interferenziale, una fase di replica a stampo su substrato polimerico e la deposizione di uno strato metallico per polverizzazione catodica. Tali sensori sono stati ottimizzati per la misura della luce trasmessa e si è analizzato il comportamento al variare dell’angolo di incidenza e dell’angolo azimutale. Si è quindi misurato il comportamento del sensore in presenza di bulk ad indici di rifrazione diversi per la stima della sensibilità, e successivamente si sono effettuate misure funzionalizzando il campione con alcantioli di diversa lunghezza. I risultati sperimentali sono stati confrontati con quelli ottenuti dalle simulazioni. Infatti si è studiato il comportamento di ogni reticolo attraverso metodi di simulazione diversi. In particolare il reticolo digitale in oro è stato studiato attraverso il metodo degli elementi finiti (FEM) implementato in COMSOL Multiphysics, il modello vettoriale è stato applicato sia per lo studio del reticolo sinusoidale in oro che del reticolo trapezoidale in argento. Quest’ultimo reticolo è stato analizzato anche attraverso il metodo RCWA (Rigorous Coupled Wave Analysis). Come già accennato, durante l’ultimo periodo di dottorato ho contribuito a sviluppare, in collaborazione con lo Spin-Off dell’università di Padova Next Step Engineering, un innovativo processo di produzione industriale che consente di creare non solo reticoli per la rilevazione di segnali plasmonici, ma anche dispositivi ibridi elettronici/microfluidici per applicazioni biologiche e mediche, all’interno di una singola linea produttiva automatizzata. Con questo processo ho prodotto i reticoli in argento, che ho utilizzato per la mia attività sperimentale. Il processo di produzione è oggetto di un brevetto italiano attualmente in fase di deposito, di cui sono uno degli inventori. Durante il dottorato ho approfondito anche lo sviluppo di dispositivi microfluidici sia attraverso tecniche di incisione polimerica, in grado di creare profili di taglio netti senza deformarne la struttura planare, sia apportando le appropriate modifiche al processo produttivo utilizzato da Next Step Engineering, precedentemente citato. I dispositivi realizzati sono stati utilizzati per le misure di bulk a diversi indici di rifrazione utilizzando i reticoli in argento.

Variable pressure electron beam etching and lithography for Teflon AF has been demonstrated. The relation between dose and etching depth is tested under high vacuum and water vapor. High resolution structures as small as 75 nm half-pitch have been resolved. Several simulation tools were tested for surface plasmon excitation. Grating based dual mode surface plasmon excitation has been shown numerically and experimentally.

Sinusoidally patterned metallic surfaces, known as plasmonic gratings, constitute one of the principal structures which allow to achieve the coupling between an incident light beam and a Surface Plasmon Polariton mode. A variety of phenomena are available when the grating is rotated of an azimuthal angle with respect to the incidence plane. Aim of this work is a comprehensive investigation of the propagation properties of the surface mode under this configuration, correlating the role of the anisotropy introduced by the grating to the position and shape of the plasmonic resonance dip in the reflectance spectra. Analytical models and physical interpretations are provided; both experimental and computational means are exploited in order to validate the models, including the observation of innovative effects. Thin-film coupled modes, the Long Range and Short Range Surface Plasmon Polaritons, are studied and experimentally observed in the azimuthally rotated configuration. Special attention is paid to the role of the plasmon radiative losses, due to the scattering by the grating. Their dependence on the grating amplitude and the plasmon propagation direction is unraveled, and correlated to the width of the observed plasmonic resonances. The outcomes of these analyses lead to the evaluation of the sensitivity and Figure of Merit achievable when the considered configurations are exploited in the framework of Surface Plasmon Resonance sensing. The developed concepts and methods are proved to be valuable tools to predict and understand the response of actual plasmonic structures applied as sensing devices against gaseous analytes. Experimental tests of the plasmonic platforms as TNT, hydrogen and aromatic compounds sensors are reported, giving promising results. A particularly remarkable experiment is the combined exploitation of Long Range modes and azimuthally rotated configuration to sensibly enhance the performance of a xylene sensor
Superfici metalliche con modulazione sinusoidale, note come grating plasmonici, costituiscono una delle principali strutture che permettono di ottenere l’accoppiamento tra un fascio di luce incidente e un Plasmone Polaritone di Superficie. Una varietà di fenomeni sono accessibili quando il grating viene ruotato di un angolo azimutale rispetto al piano di incidenza. Scopo di questo lavoro è uno studio approfondito delle proprietà di propagazione del modo di superficie in questa configurazione, correlando il ruolo dell’anisotropia introdotta dal grating con la posizione e forma del dip di risonanza plasmonica negli spettri in riflettanza. Vengono presentati modelli analitici e interpretazioni fisiche; metodi sia sperimentali che computazionali vengono impiegati per validare i modelli, includendo l’osservazione di nuovi effetti. I modi accoppiati di film sottile, ovvero i Plasmoni Long Range e Short Range, vengono studiati e osservati sperimentalmente nella configurazione ad azimuth ruotato. Una particolare attenzione è dedicata al ruolo delle perdite radiative del plasmone, dovute allo scattering da parte del grating. La loro dipendenza dall’ampiezza del grating e dalla direzione di propagazione del plasmone è spiegata, e correlata con la larghezza delle risonanze plasmoniche osservabili. I risultati di queste analisi conducono alla valutazione delle sensibilità e Figura di Merito che si possono ottenere quando le configurazioni considerate sono sfruttate nell’ambito della sensoristica a Risonanza Plasmonica di Superficie. I concetti e metodi sviluppati si dimostrano strumenti di valore per predire e interpretare la risposta di strutture plasmoniche reali, applicate come dispositivi di sensing verso analiti allo stato gassoso. Le piattaforme plasmoniche vengono testate come sensori per TNT, idrogeno e composti aromatici, con risultati promettenti. Un esperimento particolarmente interessante è l’uso combinato dei modi Long Range e della configurazione ad azimuth ruotato per incrementare notevolmente le performance di un sensore di xylene

Reflection measurements on nanoparticle arrays fabricated using electron-beam lithography confirm the predicted particle-grating interaction. An unexpected polarization-dependent splitting of the film-mediated collective resonance is successfully attributed to the existence of out-of plane polarization modes of the metal nanoparticles. In order to distinguish between the excitation of propagating surface plasmons and localized nanoparticle plasmons, spectrally resolved leakage radiation measurements are presented. Based on these measurements, a universally applicable method for measuring the wavelength dependent efficiency of coupling free-space radiation into guided surface plasmon modes on thin films is developed. Finally, it is shown that the resonantly enhanced near-field coupling the nanoparticles and the propagating surface plasmons can lead to optimized coupler device dimensions well below 10 micrometers].; The current thrust towards developing silicon compatible integrated nanophotonic devices is driven by need to overcome critical challenges in electronic circuit technology related to information bandwidth and thermal management. Surface plasmon nanophotonics represents a hybrid technology at the interface of optics and electronics that could address several of the existing challenges. Surface plasmons are electronic charge density waves that can occur at a metal-dielectric interface at optical and infrared frequencies. Numerous plasmon based integrated optical devices such as waveguides, splitters, resonators and multimode interference devices have been developed, however no standard integrated device for coupling light into nanoscale optical circuits exists. In this thesis we experimentally and theoretically investigate the excitation of propagating surface plasmons via resonant metal nanoparticle arrays placed in close proximity to a metal surface. It is shown that this approach can lead to compact plasmon excitation devices. Full-field electromagnetic simulations of the optical illumination of metal nanoparticle arrays near a metal film reveal the presence of individual nanoparticle resonances and collective grating-like resonances related to propagating surface plasmons within the periodic array structure. Strong near-field coupling between the nanoparticle and grating resonances is observed, and is successfully described by a coupled oscillator model. Numerical simulations of the effect of nanoparticle size and shape on the excitation and dissipation of surface plasmons reveal that the optimum particle volume for efficient surface plasmon excitation depends sensitively on the particle shape. This observation is quantitatively explained in terms of the shape-dependent optical cross-section of the nanoparticles.
ID: 028917015; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2010.; Includes bibliographical references (p. 111-119).
Ph.D.
Doctorate
Optics and Photonics

Neurotensin (NT) is a tridecapeptide neurotransmitter found in the central nervous system and gastrointestinal tract. Neurotensin receptor 1 (NTS1), a high affinity receptor for NT, is a member of the GPCR superfamily and is a putative target for the treatment of conditions such as Schizophrenia, Parkinson’s Disease and drug addiction. Overexpression and purification are typically limiting steps in the high resolution structure determination of GPCRs. In this study, through the optimisation of the E.coli strain used for overexpression of rat NTS1 (NTS1) and the inclusion of phospholipids in the purification buffers to prevent delipidation, an approximate 3-fold improvement in active receptor yield was obtained relative to existing protocols. Preliminary electron microscopy (negative stain and cryo) confirmed a monodisperse receptor population. Purified NTS1 is now being produced at a sufficient level for high resolution structural studies, including 3D crystallisation and further electron microscopy studies. The existing construct for the expression of NTS1 in E.coli, termed NTS1B, was modified to contain a fusion to the genes encoding either the eCFP or eYFP fluorescent proteins. These constructs were used for the E.coli expression of NTS1 tagged with either fluorescent protein at the C-terminus. Tagged receptor was successfully expressed at levels of up to 0.29 ± 0.03 mg per l of culture. Successful purification and proteolytic removal of the MBP and TrxA-His10 fusion partners was achieved whilst retaining both fluorescence and ligand binding capability (K_d = 0.91 ± 0.17 nM). Purified, fluorescent receptor was reconstituted into brain polar lipid (BPL) liposomes in an active conformation which was both fluorescent and able to bind NT. Experimentation with alternative lipid compositions suggested that specific lipids are required in order to maintain ligand-binding activity. FRET between the eCFP- and eYFP-tagged receptors was observed in reconstituted samples. The FRET efficiency was comparable to that observed in vivo for other GPCRs, including the yeast α-factor receptor, which is believed to be dimeric. This suggests that NTS1 could also be multimeric. In contrast, no FRET was observed in detergent samples. Therefore, a functioning in vitro system has been developed which enables the study of NTS1 multimerisation in lipid bilayers and future studies will attempt to implement single molecule fluorescence techniques. In addition, fluorescent derivatives of NT were successfully synthesised and purified. Radioligand competition assays and fluorescence correlation spectroscopy (FCS) confirmed that the fluorescent peptides bound to purified NTS1 in specific competition with unlabelled NT. Surface plasmon resonance (SPR) was used to confirm the ligand binding activity of purified NTS1. A novel approach was utilised which involved the measurement of the binding of detergent-solubilised NTS1 to immobilised, N-terminally biotinylated NT on the sensor surface. The use of a rigorous control, which consisted of immobilised ‘scrambled sequence’ NT, demonstrated a specific interaction. Analysis of the kinetics revealed a multiphasic interaction with a K_d in the nanomolar range. In summary, improvements to the expression and purification of NTS1, the generation of fluorescent constructs as useful tools in the study of receptor multimerisation and the optimisation of lipid-reconstitution protocols have opened up several preliminary lines of study which show considerable potential for future research.

Le développement de techniques basées sur une seule molécule au cours des dernières décennies a permis de sélectionner, de suivre et de mesurer directement une molécule individuelle. Dans cette thèse, la dynamique structurelle d'un seul émetteur quantique, servi par l'hypéricine, est caractérisée. En utilisant la microscopie à balayage confocale combinée à des modes laser polarisés radialement / azimutalement, une réorientation tridimensionnelle du moment dipolaire de transition d'une seule molécule est observée. Pour quantifier les propriétés temporelles de la tautomérie, la fonction d'autocorrélation des photons est utilisée pour extraire les fluctuations d'intensité. Les résultats montrent l'influence distincte de l'environnement local, comme la matrice PVA et l'effet de deutération. L'environnement photonique local d'une molécule est modifié par la microcavité / nanocavité. Un changement significatif du taux d'émission radiatif et des spectres de fluorescence est discuté. Il nous permet de mesurer le rendement quantique absolu en utilisant une microcavité accordable. Les résultats montrent la possibilité de contrôler la tautomérisation en modifiant l'environnement photonique. Par la suite, la dissociation moléculaire est discutée par des spectres Raman améliorés en surface à molécule unique bénéficiant de l'amélioration en champ proche de la nanocavité. Une stratégie d'optimisation expérimentale rapide vers une amélioration optimale de la fluorescence est décrite
The development of single molecule-based techniques in the last decades has enabled directly selecting, tracking, and measuring an individual molecule. In this thesis, the structural dynamics of a single quantum emitter, served by hypericin, is characterized. By using confocal scanning microscopy combined with radially/azimuthally polarized laser modes, three-dimensional reorientation of the transition dipole moment of a single molecule is observed. To quantify the temporal properties of the tautomerism, photon autocorrelation function is used to extract the intensity fluctuations. The results show the distinct influence of the local environment, such as PVA matrix and deuteration effect. The local photonic environment of a molecule is modified by the microcavity/nanocavity. A significant change of the radiative emission rate and of the fluorescence spectra is discussed. It allows us to measure the absolute quantum yield by using a tunable microcavity. The results show the possibility of controlling tautomerization by changing the photonic environment. Subsequently, molecular dissociation is discussed by single molecule surface-enhanced Raman spectra profiting from near field enhancement of nanocavity. A fast experimental optimization strategy towards optimal fluorescence enhancement is outlined

In der medizinischen Diagnostik, Bioverfahrenstechnik und Umwelttechnik besteht ein steigender Bedarf an kompakten Analysegeräten für die schnelle Vor-Ort-Detektion spezifischer biochemischer Substanzen. Im Rahmen der Arbeit wurde daher ein neuartiger faseroptischer Sensor entwickelt, der in der Lage ist kleinste Brechzahländerungen, z.B. durch molekulare Bindungsprozesse, zu detektieren. Die hohe Empfindlichkeit an der vergoldeten Spitze der Sensorfaser beruht auf der Oberflächenplasmonenresonanz (SPR) einer einzelnen Mantelmode, die durch ein langperiodisches Fasergitter (LPG) ermöglicht wird. Die Übertragungsfunktion des Sensors wurde unter Verwendung eines Schichtwellenleitermodells schnell und präzise modelliert. Es konnte gezeigt werden, dass in einem wässrigen Umgebungsmedium die höchste Empfindlichkeit im Spektralbereich um 660 nm unter Annahme einer rund 35~nm dicken und 2~mm langen Goldbeschichtung erreicht wird. Weiterhin wurde nachgewiesen, dass mit einer intermediale Schicht aus Cadmiumsulfid die SPR der Mantelmode in einen höheren Spektralbereich verschoben und damit die Empfindlichkeit deutlich verbessert werden kann. Um eine geringe Polarisationsabhängigkeit des Sensors sicherzustellen, wurde ein nasschemisches Abscheidungsverfahren für die allseitige Goldbeschichtung der Sensorfaser entwickelt. Die spezifischen optischen Eigenschaften dieser Abscheidungen wurden mit Hilfe von LPGs untersucht, die durch eine spezielle UV-Belichtung hergestellt wurden. Die Experimente ergaben, dass die komplexe Permittivität nasschemischer Abscheidungen mit Schichtdicken oberhalb von 50~nm mit aufgedampften Goldschichten vergleichbar ist. Die Verluste der adressierten Mantelmoden wurden mit einer äquivalenten Sensoranordnung aus zwei identischen LPG untersucht. Dabei konnte ein Skalierfaktor abgeleitet werden, der die effiziente Berechnung der Mantelmodendämpfung erlaubt. Es wurde nachgewiesen, dass die Brechzahlauflösung etablierter volumenoptischer SPR-Sensoren mit einer einfachen Transmissionsmessung an einer geeigneten Wellenlänge erreicht werden kann. Die äußerst kompakte Sensorfläche des faseroptischen Sensors ermöglicht darüber hinaus die Untersuchung deutlich kleinerer Probenvolumina ohne ein zusätzliches mikrofluidisches System zu benötigen. Es wurde gezeigt, dass sekundäre Brechzahländerungen aufgrund von Temperaturschwankungen oder unspezifische Ablagerungen durch eine differentielle Auswertung zweier identischer Sensoren kompensiert werden können. Die verbleibende Querempfindlichkeit wird durch die Polarisationsabhängigkeit der Sensoren bestimmt. Die geringste Querempfindlichkeit konnte daher mit einer homogenen nasschemischen abgeschiedenen Sensorfläche nachgewiesen werden
Compact analysis devices which facilitate the rapid detection of specific biochemical substances are in increasing demand in the fields of point-of-care medical diagnostics, bioprocess engineering and environmental engineering. The aim of this work was therefore to design a novel fiber-optic sensor able to detect small refractive index changes such as those caused by molecular binding processes. The high level of sensitivity at the gold-plated tip of the sensor fiber stems from the surface plasmon resonance (SPR) of a single cladding mode, which is the result of a long-period fiber grating (LPG). The transfer function of the sensor was calculated quickly and accurately using a slab waveguide model. It was observed that the highest level of sensitivity in an aqueous ambient medium is achieved at a wavelength of 660 nm assuming a gold coating of 35 nm in thickness and 2 mm in length. Furthermore, it was demonstrated that an intermedial cadmium sulfide layer shifts the SPR of the cladding mode towards higher wavelengths, thus leading to significantly enhanced sensitivity. An electroless plating process for the omnidirectional deposition of gold on the sensor fiber was developed in order to minimize the sensor\'s dependency on polarization. The specific optical properties of the gold layer deposited were investigated with the aid of LPGs fabricated using a special UV exposure method. The experiments showed the complex permittivity of electroless platings with a thickness of over 50 nm to be comparable with that of evaporated gold layers. The losses of the addressed cladding modes were investigated using an equivalent sensor setup consisting of two identical LPGs. This facilitated the determination of a scaling factor enabling the effcient calculation of cladding mode attenuation. It was demonstrated that it is possible to obtain the refractive index resolution of established volume optical SPR sensors with the aid of simple transmission measurements at a specific wavelength. Moreover, the extremely compact sensing area of the fiber-optic sensor enables the investigation of smaller sample volumes without the need for an additional microfluidic system. Secondary refractive index changes caused by temperature fluctuations or unspecific binding events can be compensated for by means of the differential interrogation of two identical fiber-optic sensors. The residual cross sensitivity is determined by the polarisation dependency of the sensor. The lowest cross sensitivity was therefore demonstrated in combination with a homogeneous electroless plated sensor surface

It is widely known that early estimates about the binding properties of drug candidates are important in the drug discovery process. Surface plasmon resonance (SPR) biosensors have become a standard tool for characterizing interactions between a great variety of biomolecules and it offers a unique opportunity to study binding activity. The aim of this project was to develop a SPR based assay for pre-screening of low molecular weight (LMW) drug compounds, to enable filtering away disturbing compounds when interacting with drugs. The interaction between 47 LMW compounds and biological ligands were investigated using the instrument BiacoreTM, which is based on SPR-technology.

碩士
國立中央大學
光機電工程研究所
101
The purpose of the dissertation is to use four-step phase shifting technique to get the phase shift of reflective light caused by the change of refraction index when grating-coupled surface plasmon resonance is processing. Whenever we do an experiment, the signal stability is often interfered by the light source and the pivot optical component. Using four-step phase shifting technique to solve these problems will be a good choose. The structure has been verified workable in our experiment. The experimental results show that the sensitivity is 1.6*10^2 (degree/RIU) and the resolution is 0.048 degree.

碩士
國立虎尾科技大學
光電與材料科技研究所
98
In this study, we used two commercialized optical simulation software programs, EM Explorer and GSolver, to conduct simulation. Calculations in the simulation were based in a finite difference time domain (FDTD) and using the rigorous coupled wave analysis (RCWA) algorithm. To confirm whether if the calculations performed by the software consisted with the theory, the Kretschmann configuration and metal grating structure were simulated, respectively. The results were then compared with the theoretical calculations of the Fresnel equation. The results showed that the calculated results by the two software programs met with the theory. Further on we simulated and designed two types of grating coupler electro-optic modulators. The first type was an inverse grating structure, where simulation results showed the resonance angle was 22.98°, full width at half maximum (FWHM) was approximately 0.07°. When the refractive index of the EO polymer layer changed to 0.0015, the resonance angular shift was 0.06°. The incident angle was fixed at 22.98°, with an applied 9.09 V to enable the reflectivity change from 4 % to 69 %, which a voltage around 4.5 V can achieve 50% of modulation index; the second was a grating coupler with a long-range surface plasmon structure. Simulation results showed the resonance angle was 35.81°, FWHM approximately 0.05°. When the refractive index of the EO polymer layer changed to 0.0007 the resonance angular shift was 0.06°. The incident angle was fixed at 35.81°, with an applied 10.61 V to enable the reflectivity change from 1% to 60 %, which a voltage around 5 V can achieve 50 % of modulation index.

Complex biological samples such as serum contain thousands of proteins and other molecules spanning up to 13 orders of magnitude in concentration. Present measurement techniques such as protein microarrays and quantum dot FRET do not permit the analysis of all pair-wise interactions between the components of such a complex mixture to a given target molecule. In this thesis, we explore the use of nanoparticle tags which encode the identity of the molecule to obtain the statistical distribution of pair-wise interactions using their Localized Surface Plasmon Resonance (LSPR) signals. The encoding is done through choice of shape, size and material of the nanoparticles. Protein interactions produce plasmonic coupling between pairs of such particles which are well resolved in the scattering spectra. In this thesis, we analyze the multiplexing capacity of such an approach and compare it with a FRET based method. It is observed that multiplexing capacity is significantly higher for plasmonic coupling based method proposed in this thesis compared to the use of commonly available FRET pairs. One of the practical disadvantages of single nano-particle resolved plasmonic sensing is the low scattering intensity causing a deteriorated signal to noise ratio of detection. As part of this work, we investigated the effect of substrate on light scattering from the nanoparticle and showed that high reflectivity substrates with field reflection coefficients approaching unity result in nearly an order of magnitude enhancement of scattered light intensity. Going further on the practical realizations of plasmonic sensors, we analyzed Grating Coupled Surface Plasmon Resonance (GC-SPR) sensors based on commercially available DVD gratings using Rigorous Coupled Wave Analysis (RCWA) technique implemented in the numerical package R-Soft. We showed that by using a multi-layer dielectric coating the linewidth of the plasmonic response can be reduced by more than an order of magnitude, consequently enhancing the limit of detection of the DVD based sensor.

碩士
國立臺灣科技大學
電子工程系
103
Surface plasmon resonance (SPR) is a physical phenomenon that happens between the interface of metal and non-conductive materials and can be induced by external electrons or photons injection. When the light wave is propagating from the high to low refractive index in the material and the incident angle is larger than the total internal reflection, the free electrons in the metal will be excited and resonate in the longitudinal direction at the specific angle. The attenuated total reflection is typically utilized to generate the non-radiative surface plasmon wave. We can say that the incident light angle is large than the total internal reflection, the evanescent wave in the transmitted medium will penetrate into half of the wavelength. When the propagation constants between the evanescent and surface plasmon waves are the same, the surface plasmon resonance is happening and the reflective light will rapidly drop to the minimum. By applying this feature onto the biosensing applications, the real-time, high sensitivity and label-free detection are possessed. Therefore, it has been extensively utilized in bio-detection and immunochemistry for its efficiency in analyzing the small refraction index variation of detected materials. Typically there are two modulations, angle and wavelength, for surface plasma resonance, which were sensing the analytes using the smallest reflection at the resonance angle and wavelength. In this thesis, the 1550-nm wavelength for fiber optic communications, used as the light source, was injected on the prism interface to generate the surface plasmon between the metal and non-metal materials. The SPR wavelength modulation was implemented by the fiber-optic communication wavelengths due to its deep penetration depth and high sensitivity compared with the visible light. In this thesis the biosensor will only explore the prism coupling with the wavelength modulation for characterize the surface plasmon resonance. In order to sense the small amount of analytes, such as short base pair synthetic miR-21 DNA, the waveguide coupled surface plasmon resonance demonstrated more sensitivity than the traditional one because of its additional guided wave and metal layers to enhance the evanescent wave between the layers of metal and guide wave for narrow reflective spectrum. After the simulation from the commercial software Matlab, the full width at half maximum from the waveguide coupled surface plasmon resonance is 2.11 times than the tradition one. The system resolution is also improved up to 2.13 times for better sensitivity in biosensing. Our experimental data showed that the thickness of metal directly on the prism would significantly affect the linewidth. On the other hand, the wavelength modulation sensitivity on the waveguide coupled surface plasmon resonance is less sensitive to injected angle variation compared with the traditional one.

This dissertation consists of two topics. One is a "Multi-pass Fiber Optic Surface Plasmon Resonance Sensor (SPR)" and the other is a "Nano-metallic Surface Plasmon Lens." Since both topics involved surface plasmon, the title of this dissertation is named "Surface plasmon coupled sensor and nanolens." For a multi-pass fiber optic SPR sensor, a fiber optic 4-pass SPR sensor coupled with a field-assist capability for detecting an extremely low concentration of charged particles is first demonstrated. The multipass feature increases the sensitivity by a factor equal to the number of passes. The field-assist feature forces charged particles/molecules to the SPR surface, increasing the sensitivity by an additional factor of about 100. Overall, the sensitivity exceeds the one-pass SPR device by a factor of about 400. A 10 pM concentration of 47 nm diameter polystyrene (PS) latex beads and 1 ?M concentration of salt dissolved in DI water were detected within a few seconds by the combined system. The equivalent index resolution for atomic size corresponding to ionized chlorine in salt is 10-8. This technique offers the potential for sensitive and fast detection of biomolecules in a solution. Secondly, a 44-pass fiber optic surface plasmon resonance (SPR) sensor coupled with a field-assist capability for measurement of refractive index change due to positive and negative ions is shown. The field-assist feature forces ions to the SPR surface, causing the SPR signal response to change which reflects a decrease or increase in refractive index depending on whether positive or negative ions are being attracted to the surface. This technique offers the potential for the sensitive detection of cations and anions in a solution. For a nano-metallic surface plasmon lens, we analyze the transmission of a normally incident plane wave through an Ag/dielectric layered concentric ring structure using finite difference time domain (FDTD) analysis. The dependency of the transmission efficiency on the refractive index in slit is studied. The numerical analysis indicates that the focusing beyond diffraction limit is found even at the extended focal length comparable to the distance of 7" from the exit plane using a circularly polarized coherent plane wave, ?=405 nm. Especially, compared to an Ag-only structure, the Ag/ LiNbO3 structure amplifies the transmission power by a factor of 6. Therefore, this Ag/dielectric layered lens has the potential for significantly higher resolution imaging and optical data storage.

碩士
國立臺灣大學
光電工程學研究所
107
Based on highly Ga-doped ZnO (GaZnO) thin films of different thicknesses on sapphire substrate, grating structures of different grating ridge depths but with a fixed grating period at 1100 nm are fabricated for studying their surface plasmon polariton (SPP) and localized surface plasmon (LSP) resonance behaviors through the reflection and transmission measurements with light incident from top (air side) and bottom (sapphire side). When GaZnO thin film is thick (300 nm), the SPP and LSP features can be observed only from top through reflection measurement. When GaZnO thin film becomes thinner, the SPP and LSP features can be observed from top and bottom through either reflection or transmission measurement. However, the observed SPP and LSP features from top and bottom are slightly different due to the different effects of air and sapphire. When the grating structure consists of periodic isolated GaZnO islands, no SPP or LSP can be observed unless the ridge height is large enough for supporting LSP. Simulation studies are performed to well support the experimental data.

碩士
國立中央大學
機械工程研究所
91
Due to the increasing demand for the development of light modulator with larger bandwidth and higher efficiency in the optical communication, in this thesis we present a novel ultrahigh efficiency and high dynamic response light modulator based on an external applied voltage to modulate the excitation degree of incident waveguide light in surface plasmons (SPs), known as the attenuation total reflection method (ATR method). This waveguide-coupled surface plasmon light modulator is fabricated by spin coating an organic electro-optic (E-O) polymer film onto the metal layer with suitable thickness of 30~40 nm, and then deposited a bottom metal electrode under the polymer. The molecular orientation of E-O polymer is aligned into noncentro-symmetry structure by applying contact poling process. When an external applied electric field created a linear variation of refractive index of poled E-O polymer according to the Pockels effect, the excitation degree of incident waveguide light in surface plasmons is changed and then the reflected light is modulated. Besides, we present in the thesis an optimizing design principle for efficient light modulator through the concentration of engery by waveguide coupled, surface plasmons, electro-optic effect, simulation, and theory analysis. To accurately determine the reflective index, attenuation coefficient, and the thickness of the metal layer, we analyzed the ATR spectra by techniques including Lorentzian equation analysis, Fresnel’s equation data-fitting and optimal linear data analysis. Alternatively, by using least square data-fitting techniques which employ two waveguide mode, we could calculate the refractive index and thickness of electro-optic polymer. We also estimated the attenuation coefficient of the polymer by anaylzing the reflection minimum of ATR spectrum. Finally, we calculated its actual electro-optic coefficient of this modulator by analyzing both E-O pockels effect and ATR spectrum. However, because the modulator fabricated in our experiment is not on optimum condition, the results so far show only 1% modulation in the intensity of the reflected light with driving voltage 30V. Finally, we present a novel and high efficiency electro-optic light modulators based on long range surface plasmon wave coupled with classical surface plasmon wave. Due to the excitation of surface plasmon wave, the energy is concentrated in the waveguide, so the efficiency could be improved. By simulation, it could effectively reduce driving voltage and increase the modulation index of 70 % with driving voltage 10 V.

碩士
國立成功大學
機械工程學系碩博士班
95
As for the application on optical fiber sensor, we combine the advantages of traditional LPG sensor and present prism coupler surface plasmon resonance (SPR) sensor. Now we further propose a novel type of optical fiber SPR sensor. It simply employs a long-period fiber grating with proper period to couple a core mode to the co-propagating cladding mode that can excite surface plasmon wave (SPW) and monitors the change of the transmitted core mode power, which is operating at a fixed wavelength, to determine the variation of the refractive index of analyte. As far as the excitation of SPW, the model of numerical simulation, and the complexity of measurement equipment are concerned. In this dissertation, we derive the dispersion relation of guiding modes in this four-layer optical-fiber SPR sensor, and the unconjugated form of coupled-mode equations. In order to increase greatly the efficiency on analyzing this new SPR sensor, further simplifications on the integration form of coupling constants are proposed. In addition, we also do some basic experiment to confirm its application. In order to understanding more about our specific period, we also discuss about the relationship between mode order and period of LPG by simulating. We calculate from two aspects which are period fixed and cladding mode order fixed to inspect the affect between each other. From the results of simulation, we can plot diagrams of the cladding mode order against grating period and effective refractive index in cladding mode against the period of grating for resonant wavelength at 1550 nm. In aspects of mathematics and physics, all cladding modes exist possibly by solving the structure of fiber through arithmetic equations. But to be concerned with practicality, it is impossible to control the cladding modes independently and accurately.

We report on the development and on the first use of the widefield surface plasmon (WSPR) microscope in the examination of the cell surface interface at submicron lateral resolutions. The microscope is Kohler illuminated and uses either a 1.45 numerical aperture (NA) oil immersion lens, or a 1.65 NA oil immersion lens to excite surface plasmons at the interface between a thin gold layer and a glass or sapphire cover slip. Like all surface plasmon microscope systems the WSPR has been proven in previous studies to also be capable of nanometric z-scale resolutions. In this study we used the system to image the interface between HaCaT cells and the gold layer. Imaging was performed in air using fixed samples and the 1.45 NA objective based system and also using live cells in culture media using the 1.65 NA based system. Imaging in air enabled the visualisation of high resolution and high-contrast submicron features identified by vinculin immunostaining as component of focal contacts and focal adhesions. In comparison, imaging in fluid enabled cell surface interfacial interactions to be tracked by time-lapse video WSPR microscopy. Our results indicate that the cell surface interface and thus cell signalling mechanisms may be readily interrogated in live cells without the use of labelling techniques.

碩士
國立虎尾科技大學
光電工程系光電與材料科技碩士班
106
This paper proposes a back-side incident grating coupled structure that can be fabricated using nanoimprint technology. This component has a flat surface and is suitable for sensing the attachment properties of biological cells. We also compare this component with the conventional front-side incident grating coupled structure and analyze the characteristics and sensitivity of the intensity and phase detection of these two different grating coupled surface plasmon resonance elements as sensors. The simulation results show that the sensitivity performance of these two sensors is similar. For the back-side incident sensor, the light will not pass through the material under test during sensing. Besides, the surface is a flat structure, comparing with the grating surface, there will be no surface profile effect when the material under test is attached to the component. We used a low-refractive-index material as the grating structure and it is fabricated on the substrate by nanoimprint technology. Then, a layer of titanium dioxide (TiO2) is sputtered on the surface. The film is combined with a sol-gel method to deposit a titanium dioxide (TiO2) solution on the grating, and finally a layer of gold (Au) is evaporated to form a surface plasma resonance element structure. In order to detect phase changes, we use heterodyne interference technology to match the phase change of the phase-locked amplifier recording component, and use Labview automation program to combine automatic measurement with stepper motor, optical power meter, lock-in amplifier and computer.

碩士
國立臺灣大學
應用力學研究所
93
Grating coupling is a major method to excite surface plasmon resonance; this thesis took the extraordinary transmission phenomenon first proposed by Ebbesen et al. as the starting point to study gratings of different materials and various profiles in order to understand the influence of these changes on surface plasmon resonance. It is anticipated to utilize parameters learned during the course of this research to facilitate the design of nanowriter optical head and other related applications. In simulations, we use rigorous coupled wave analysis (RCWA) and finite difference time domain (FDTD) to calculate the reflection spectrum and electromagnetic mode of surface plasmons, both of which is coupled by using gratings. The surface plasmon dispersion curve and coupling efficiency under different grating profiles were successfully calculated. We consider the non-metal surface gratings as a homogeneous dielectric layer by using effective medium theory. For metal surface gratings, we found the surface plasmon resonance condition of gradient gratings is different to binary gratings, thus the coupling efficiency and band gap width of gratings under different grating depths will be different. The distribution of electromagnetic field under different wavelength of light will be different. More specifically, the coupling efficiencies and band gap width under different grating depth were found to be different. We can obtain the design criterion of optical head and other optical devices through the above simulations. In experiments, we use electron beam lithography to make the gradient gratings, and produce metal and non-metal surface gratings with proper fabrication process. The fabrication process of nanowriter optical head was then detailed. We also take advantage of wet etching to manufacture the triangular nanoimprint mold with an attempt to reach the mass production goal of nanowriter optical head and other applications by using nanoimprint techniques.

碩士
長庚大學
光電工程研究所
96
The characterization of optical and electrical properties of quantum dot like (QD-like) in InGaN/GaN multiple quantum well heterostructures have been investigated. From the temperature-dependent photoluminescence spectra, it has been carried out regarding the introduction of hydrogenation reduction not only to encourage indium atoms coherence motion tend three-dimensional cluster formations to form QD-like nanostructures, but also to provide better confine ability to enhance the exciton radiative recombination and increase the light output intensity. The time-resolved photoluminescence temporal decays of QW emission were investigated to examine the dynamics of the exciton recombination. It further shows the exciton with longer lifetime for the stronger localization effect QD-like structures due to the improvement of lattice mismatch and the reduced defect density that exciton trapped in deep or shallow energy states. Utilizing the band diagram theory method, the optical behavior of PL spectra of different QD-like structures can be well explained after introducing the hydrogenation reduction process. With increasing the injection current, the blue-shift of electroluminescence (EL) peak energy spectra induced by stronger screening effect was augmented in the multiple quantum wells. The radiative recombination mechanism and other devices performance will be discussed in detail in this study.

博士
國立成功大學
電腦與通信工程研究所
94
In the recent years, utilizing the spectrum characteristic of long-period fiber grating (LPG), numerous components extensively applied on optical fiber communication system have been proposed such as band rejection filters, gain flatteners, and dispersion compensators. In contrast to fiber Bragg grating, it is well-known that the LPG has considerable spectrum bandwidth. So far, on the optical communication component design, the researches as to LPG are all to emphasize the coupling characteristic between core mode HE11 and low order cladding modes. Obviously, it is almost impossible to use LPG to design the optical communication components that possess the narrow bandwidth and conform Wavelength Division Multiplexing standard (WDM), not to mention Dense Wavelength Division Multiplexing standard (DWDM). In this dissertation, we use strict coupled-mode theory to study and quantify the spectrum characteristic of LPG in detail with the aim of supplying a concrete concept to design narrow-bandwidth optical communication components. In contrast to the wide spectrum bandwidth resulting from the coupling between core mode and low order cladding modes, we will prove that a 0.4 nm FWHM can be achieved as long as the period of LPG is properly designed to choose some high order cladding. Then, we will further apply this new concept to design the narrow bandwidth optical add-drop multiplexer (OADM) based on two parallel LPGs. In addition, in order to obtain the maximal power transmission, we also derive the structure parameters of OADM such as the distance between two parallel fibers and the length of two LPGs according to four-mode coupled-mode equations. As for the application on optical fiber sensor, we combine the advantages of traditional LPG sensor and present optical-fiber surface-plasmon-resonance (SPR) sensor and further propose a new type of optical-fiber SPR sensor. It simply employs a long-period fiber grating with proper period to couple a core mode (HE11) to the co-propagating cladding mode that can excite surface plasmon wave (SPW) and monitors the change of the transmitted core mode power, which is operating at a fixed wavelength, to determine the variation of the refractive index of analyte. As far as the excitation of SPW, the model of numerical simulation, and the complexity of measurement equipment are concerned, it is obvious that this new structure is superior to the proposed SPR sensor, consisting of a bent polished single-mode SPR optical fiber. In this dissertation, we derive the dispersion relation of guiding modes in this four-layer optical-fiber SPR sensor, and the unconjugated form of coupled-mode equations. In addition, in order to increase greatly the efficiency on analyzing this new SPR sensor, further simplifications on the integration form of coupling constants are proposed. The numerical results will demonstrate that this new and simple configuration may be used as a highly sensitive amplitude-sensor. Furthermore, it can be easily adapted for a SPR fiber optical probe by depositing a mirror on the fiber tip.

In der medizinischen Diagnostik, Bioverfahrenstechnik und Umwelttechnik besteht ein steigender Bedarf an kompakten Analysegeräten für die schnelle Vor-Ort-Detektion spezifischer biochemischer Substanzen. Im Rahmen der Arbeit wurde daher ein neuartiger faseroptischer Sensor entwickelt, der in der Lage ist kleinste Brechzahländerungen, z.B. durch molekulare Bindungsprozesse, zu detektieren. Die hohe Empfindlichkeit an der vergoldeten Spitze der Sensorfaser beruht auf der Oberflächenplasmonenresonanz (SPR) einer einzelnen Mantelmode, die durch ein langperiodisches Fasergitter (LPG) ermöglicht wird. Die Übertragungsfunktion des Sensors wurde unter Verwendung eines Schichtwellenleitermodells schnell und präzise modelliert. Es konnte gezeigt werden, dass in einem wässrigen Umgebungsmedium die höchste Empfindlichkeit im Spektralbereich um 660 nm unter Annahme einer rund 35~nm dicken und 2~mm langen Goldbeschichtung erreicht wird. Weiterhin wurde nachgewiesen, dass mit einer intermediale Schicht aus Cadmiumsulfid die SPR der Mantelmode in einen höheren Spektralbereich verschoben und damit die Empfindlichkeit deutlich verbessert werden kann. Um eine geringe Polarisationsabhängigkeit des Sensors sicherzustellen, wurde ein nasschemisches Abscheidungsverfahren für die allseitige Goldbeschichtung der Sensorfaser entwickelt. Die spezifischen optischen Eigenschaften dieser Abscheidungen wurden mit Hilfe von LPGs untersucht, die durch eine spezielle UV-Belichtung hergestellt wurden. Die Experimente ergaben, dass die komplexe Permittivität nasschemischer Abscheidungen mit Schichtdicken oberhalb von 50~nm mit aufgedampften Goldschichten vergleichbar ist. Die Verluste der adressierten Mantelmoden wurden mit einer äquivalenten Sensoranordnung aus zwei identischen LPG untersucht. Dabei konnte ein Skalierfaktor abgeleitet werden, der die effiziente Berechnung der Mantelmodendämpfung erlaubt. Es wurde nachgewiesen, dass die Brechzahlauflösung etablierter volumenoptischer SPR-Sensoren mit einer einfachen Transmissionsmessung an einer geeigneten Wellenlänge erreicht werden kann. Die äußerst kompakte Sensorfläche des faseroptischen Sensors ermöglicht darüber hinaus die Untersuchung deutlich kleinerer Probenvolumina ohne ein zusätzliches mikrofluidisches System zu benötigen. Es wurde gezeigt, dass sekundäre Brechzahländerungen aufgrund von Temperaturschwankungen oder unspezifische Ablagerungen durch eine differentielle Auswertung zweier identischer Sensoren kompensiert werden können. Die verbleibende Querempfindlichkeit wird durch die Polarisationsabhängigkeit der Sensoren bestimmt. Die geringste Querempfindlichkeit konnte daher mit einer homogenen nasschemischen abgeschiedenen Sensorfläche nachgewiesen werden.
Compact analysis devices which facilitate the rapid detection of specific biochemical substances are in increasing demand in the fields of point-of-care medical diagnostics, bioprocess engineering and environmental engineering. The aim of this work was therefore to design a novel fiber-optic sensor able to detect small refractive index changes such as those caused by molecular binding processes. The high level of sensitivity at the gold-plated tip of the sensor fiber stems from the surface plasmon resonance (SPR) of a single cladding mode, which is the result of a long-period fiber grating (LPG). The transfer function of the sensor was calculated quickly and accurately using a slab waveguide model. It was observed that the highest level of sensitivity in an aqueous ambient medium is achieved at a wavelength of 660 nm assuming a gold coating of 35 nm in thickness and 2 mm in length. Furthermore, it was demonstrated that an intermedial cadmium sulfide layer shifts the SPR of the cladding mode towards higher wavelengths, thus leading to significantly enhanced sensitivity. An electroless plating process for the omnidirectional deposition of gold on the sensor fiber was developed in order to minimize the sensor\'s dependency on polarization. The specific optical properties of the gold layer deposited were investigated with the aid of LPGs fabricated using a special UV exposure method. The experiments showed the complex permittivity of electroless platings with a thickness of over 50 nm to be comparable with that of evaporated gold layers. The losses of the addressed cladding modes were investigated using an equivalent sensor setup consisting of two identical LPGs. This facilitated the determination of a scaling factor enabling the effcient calculation of cladding mode attenuation. It was demonstrated that it is possible to obtain the refractive index resolution of established volume optical SPR sensors with the aid of simple transmission measurements at a specific wavelength. Moreover, the extremely compact sensing area of the fiber-optic sensor enables the investigation of smaller sample volumes without the need for an additional microfluidic system. Secondary refractive index changes caused by temperature fluctuations or unspecific binding events can be compensated for by means of the differential interrogation of two identical fiber-optic sensors. The residual cross sensitivity is determined by the polarisation dependency of the sensor. The lowest cross sensitivity was therefore demonstrated in combination with a homogeneous electroless plated sensor surface.