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Protein adsorption monitored by plasmon-enhanced semi-cylindrical Kretschmann ellipsometry
Abstract
The Kretschmann-Raether geometry is widely used to investigate the properties of various biological samples and their behavior on different substrates ###citearw11a (mostly on gold surface with/without different functionalization). In this configuration the surface plasmon polaritons (SPPs) are used to enhance the sensitivity of the measurement. Recently, the combination of this method with spectroscopic ellipsometry (SE) became more and more popular. In our work protein adsorption was monitored in situ using this configuration. The performance of the configuration was investigated for different thicknesses of the plasmonic layer. The best measurement parameters were identified in terms of layer thickness, angle of incidence (AOI) and wavelength range. It was shown that the spectroscopic capability over a broad wavelength range, the possibility to adjust the AOI accurately, as well as the phase information from the measurement proves to be a significant advantage compared to standard configuration and surface plasmon resonance configurations.
... If appropriate conditions are fulfilled, the incident light couples with surface plasmons, thus a dip appears in the reflectance spectrum. The exact wavelength ( ) value of this dip is highly dependent on the thickness (d) and optical properties of the Au layer [6], the angle of incidence ( ) of the light beam, the optical properties of the configuration and most importantly the optical properties of the investigated ambient near the Au surface. ...
... The FS slides used for the 40 nm Au layers were identical to those of the BMS. For Au layer plasmonics = d 40 nm was chosen as the most sensitive one, based on previous results from Ref. [6]. The thin Au layer was also characterized by SE at = 60, 65 and 70°, and the result of a transmission intensity measurement was fitted simultaneously. ...
... Fgn Fgn PBS (6) where n PBS is the refractive index of the PBS ambient, and a denotes the refractive index increment of the Fgn solution (n s ) with the Fgn concentration (dn s /dc Fgn ) at the wavelength value of 632.8 nm. The value of a was fixed at 0.18 mL/g. ...
We designed a Bragg mirror structure with an SiO2 top layer to create a resonance in the ultraviolet wavelength range, near the absorption peak position of various proteins. We demonstrate that the wavelength of enhanced sensitivity can be adjusted by proper design of the 1D photonic structure. The possibility to design the wavelength of enhanced sensitivity supports measurements of better selectivity, optimized for the absorption of the target material. Since the width of the resonant peak in the reflectance spectra can be sharper than those of plasmonics, and they can be positioned at more favourable regions of the instrument and material (e.g., in terms of intensity or selectivity), the sensitivity can exceed those of plasmon-enhanced measurements. In this study we demonstrate the main features of the concept at the example of in situ spectroscopic ellipsometry of fibrinogen adsorption in the Kretschmann-Raether configuration. We realized a resonant peak with a full width at half maximum of 3 nm near the wavelength of 280 nm, which coincides with the absorption maximum of fibrinogen. The influence of depolarization and surface roughness on the measurements, and the potential for improving the current experimental detection limit of 45 pg/mm² is also discussed.
... Sensitivity in a plasmon-enhanced Kretschmann geometry using only the amplitude information (fitting only on the ellipsometric angle of Ψ ) or both the amplitude and phase information (fitting on both Ψ and ∆) [73]. ...
... There are two major advantages of this method. (i) The wavelength of resonance can be custom-designed by using proper material stacks and thicknesses, whereas by plasmonic layers the position of resonance cannot be shifted below or above a certain limit [73]. (ii) Using a Bragg structure the surface layer can be chosen to be a dielectric that may play an important role in the surface chemistry. ...
... The next issue is that for a high-sensitivity measurement the refractive index of all the media (e.g. the water, the gold layer, the glass of the hemi-cylinder) have to be known very accurately (see e.g. Fig. 3 in Ref. [73]). Since the properties of these materials may depend on the preparation conditions, the stress or possible contaminations, the use of proper references is a great challenge. ...
Understanding interface processes has been gaining crucial importance in many applications of biology, chemistry, and physics. The boundaries of those disciplines had been quickly vanishing in the last decade, as metrologies and the knowledge gained based on their use improved and increased rapidly. Optical techniques such as microscopy, waveguide sensing, or ellipsometry are significant and widely used means of studying solid‐liquid interfaces because the applicability of ions, electrons, or X‐ray radiation is strongly limited for this purpose due to the high absorption in aqueous ambient. Light does not only provide access to the interface making the measurement possible, but utilizing the phase information and the large amount of spectroscopic data, the ellipsometric characterization is also highly sensitive and robust. This article focuses on ellipsometry of biomaterials in the visible wavelength range. The authors discuss the main challenges of measuring thickness and optical properties of ultra‐thin films such as biomolecules. The authors give an overview on different kinds of flow cells from conventional through internal reflection to combined methods. They emphasize that surface nanostructures and evaluation strategies are also crucial parts of in situ bioellipsometry and summarize some of the recent trends showing examples mainly from their research.
... There are various different approaches to prepare plasmonic nanoparticles for sensing including bulk chemical [11], electrochemical [41], physical deposition [15,[42][43][44][45], self-assembly [24], the formation of nanoaggregate containers [46] or porous nanoparticles [47], ordered adsorption, holographic methods [48], colloid chemistry [49][50][51][52][53], ligand-controlled assembly [54], nanosphere assembly [55,56] and lithography [57], composites with polymers [58], combination with other plasmonic [59] or 2D materials [60], electron beam lithography or ion beam methods [31]. Each method has its advantages in terms of cost, speed, reliability, sensitivity, adjustability, etc. ...
... (i) It is simple, requiring only a thin gold layer's deposition and subsequent annealing at a few hundred • C [16,63,64]. (ii) The LSPRs can be optically generated in simple transmission cells, avoiding the application of the Kretschmann-Raether configuration [43,65,66]. (iii) Gold is stable with no formation of a surface oxide layer. ...
... Recently, biosensors based on optical and electrical transducers have shown great potentials to overcome these limitations [5,6]. In recent years, spectroscopic ellipsometry has gained great interest and attention in the bio-sensing field due to its real-time, label-free and non-destructive measurement method [7,8]. Over the past several years, the ellipsometry technique was used for various biological studies. ...
... [16]. There are two main configurations for propagation of surface plasmons, grating-based and prism-based configurations [7,17]. In this study, we use a Kretschmann flow cell geometry which is shown in Fig. 1. ...
In this work, we investigate whether bacteria can be substantially examined in liquid environment with an ellipsometer in the visible wavelength range. For that investigation a Kretschmann type flow cell was used in which the paths of illuminated and reflected light beams are on the substrate side. To enhance the sensitivity a thin gold layer was applied on the top of glass substrate and the measurement was performed by using surface plasmon polaritons. Porphyrin functionalized coating layers were employed to analyze their performance to capture bacteria and to study the stability and repeatability of the optical response with regard to the ellipsometric measurement. Escherichia coli (E. coli) bacteria were used as first model bacteria and their deposition on the sensing surface was monitored in a real-time measurement in a liquid environment.
... Using ellipsometry, they have shown that the deposition plays a significant role in output values of Δ and Ψ parameters. In 2017, Kalas et al. (2017) have monitored the fibrinogen adsorption on thin gold film using broadband light and various incident angles (Fig. 3c). They have shown that the employment of broad incident wavelengths as well as a range of incident angles provided an optimal adjustment for highly sensitive monitoring. ...
... In 2014, Garcia-Marin et al. (2014) have detected small molecules of glutathione (GSH) using Al-doped ZnO (AZO)/Au bilayer on transparent substrate that was functionalized (Diest et al. 2013). c Ellipsometry parameters before and after the fibrinogen deposition on the sensing chip at the incident angle of 70° (Kalas et al. 2017). d Designed and fabricated chamber for recording the neural signal under electrical stimulation using plasmonic-ellipsometry. ...
Plasmonic biosensing endeavors to offer the ultrasensitivity below 10−7 RIU along with providing a label-free platform for the detection of biomarkers. Integrating the intensity (amplitude) sensing with phase property of light not only can increase the signal to noise ratio but also provides additional information of the phase changes compared to the conventional plasmonic technique. This information can be helpful for in-depth understanding of the biomolecular and cellular interactions of the sample. In this review, we aim to look into the recent works on plasmonic biosensing based on phase-sensitive ellipsometry technique and investigate the various structures that have been provided for this platform up to now. The structures based on thin films, colloids and disordered systems, nanoparticle/nanhole arrays, graphene and 3D structures have been reviewed. Undoubtedly, choosing a structural platform and optimizing its structural parameters can increase the biosensitivity as well as decreasing the limit of detection that plays a key role in biosensing. Due to the vast area of phase-sensitive plasmonics, we limit our focus to ellipsometry technique and its integration with plasmonics. We hope this review can open up new horizons towards the development and fabrication of highly sensitive plasmonic structures applicable in phase-sensitive biosensing.
... Another interesting venture is the combination of GCI with spectroscopic ellipsometry (GCI-SE) in one instrument, which may offer the simultaneous exploitation of the high sensitivity provided by GCI and the spectroscopic capabilities of SE, allowing complex multilayer structures to be analyzed in detail [278]. SE-SPR is a (i) type combination realizing the generation of surface plasmons and simultaneous SE measurement in the proper configuration [279][280][281][282][283]. Whether the data are obtained from (i) or (ii), the postmeasurement combination of QCM and optical data are present complex data analysis challenges. ...
Bacteria repellent surfaces and antibody-based coatings for bacterial assays have shown a growing demand in the field of biosensors, and have crucial importance in the design of biomedical devices. However, in-depth investigations and comparisons of possible solutions are still missing. The optical waveguide lightmode spectroscopy (OWLS) technique offers label-free, non-invasive, in situ characterization of protein and bacterial adsorption. Moreover, it has excellent flexibility for testing various surface coatings. Here, we describe an OWLS-based method supporting the development of bacteria repellent surfaces and characterize the layer structures and affinities of different antibody-based coatings for bacterial assays. In order to test nonspecific binding blocking agents against bacteria, OWLS chips were coated with bovine serum albumin (BSA), I-block, PAcrAM-g-(PMOXA, NH2, Si), (PAcrAM-P) and PLL-g-PEG (PP) (with different coating temperatures), and subsequent Escherichia coli adhesion was monitored. We found that the best performing blocking agents could inhibit bacterial adhesion from samples with bacteria concentrations of up to 107 cells/mL. Various immobilization methods were applied to graft a wide range of selected antibodies onto the biosensor's surface. Simple physisorption, Mix&Go (AnteoBind) (MG) films, covalently immobilized protein A and avidin-biotin based surface chemistries were all fabricated and tested. The surface adsorbed mass densities of deposited antibodies were determined, and the biosensor;s kinetic data were evaluated to divine the possible orientations of the bacteria-capturing antibodies and determine the rate constants and footprints of the binding events. The development of affinity layers was supported by enzyme-linked immunosorbent assay (ELISA) measurements in order to test the bacteria binding capabilities of the antibodies. The best performance in the biosensor measurements was achieved by employing a polyclonal antibody in combination with protein A-based immobilization and PAcrAM-P blocking of nonspecific binding. Using this setting, a surface sensitivity of 70 cells/mm2 was demonstrated.
... Another interesting venture is the combination of GCI with spectroscopic ellipsometry (GCI-SE) in one instrument, which may offer the simultaneous exploitation of the high sensitivity provided by GCI and the spectroscopic capabilities of SE, allowing complex multilayer structures to be analyzed in detail [278]. SE-SPR is a (i) type combination realizing the generation of surface plasmons and simultaneous SE measurement in the proper configuration [279][280][281][282][283]. Whether the data are obtained from (i) or (ii), the postmeasurement combination of QCM and optical data are present complex data analysis challenges. ...
Interfacial layers are important in a wide range of applications in biomedicine, biosensing, analytical chemistry and the maritime industries. Along with the growing number of applications, the analysis of these layer properties and understanding their behavior is becoming crucial. Label-free surface sensitive methods are excellent tools to monitor the structure and formation kinetics of thin layers in real-time even at the nanoscale. In this study, we review the available label-free techniques and demonstrate how the experimentally obtained data can be utilized to extract kinetic and structural information about the formed layers. We outline the most traditional and some novel techniques using optical and mechanical transduction principles. With a special focus, we review the current possibilities o the combination of label-free methods which is a powerful tool to extend the range of detected parameters. We summarize the most important theoretical considerations for obtaining reliable information from measurements taking place in liquid environments and hence layers in a hydrated state. Detailing with both structural and kinetic analysis methods, a thorough overview of the various quantities obtained from the evaluation of the raw label-free data are also provided. Here, thickness, refractive index, optical anisotropy and the related chain orientation, hydration degree, viscoelasticity, footprint, association and dissociation rate constants are all mentioned in detail. To demonstrate the effect of variations in model conditions on the observed data, simulations of kinetic curves at various model settings are also included. Based on our own experience with optical waveguide lightmode spectroscopy (OWLS) and the quartz crystal microbalance (QCM), we have developed software packages for data analysis. Along with this paper, we make the developed software available for the wider scientific community.
... 13 Most in situ IRSE solutions utilize highly transparent bulk materials in configurations that either enable the deflection of the light reflected from the outer surface of the cell 11 or ensure that there is no change of the ellipsometric angles, such as in the case of Kretschmann−Raether configurations. 13,32, 33 The third possibility is to make a compromise with the given optical properties but using a thin-walled cell through which the absorption is acceptable. This leads to a microfabrication method described in the Microfabrication of a Membrane-Based Flow Cell for IRSE section that makes it possible to prepare a membrane cell with thicknesses down to a few microns. ...
Mid-infrared (IR) ellipsometry of thin films and molecule layers at solid–liquid interfaces has been a challenge because of the absorption of light in water. It has been usually overcome by using configurations utilizing illumination through the solid substrate. However, the access to the solid–liquid interface in a broad spectral range is also challenging due to the limited transparency of most structural materials in the IR wavelength range. In this work, we propose a concept of a microfabricated analysis cell based on an IR-transparent Si membrane with advantages of a robust design, flexible adaptation to existing equipment, small volume, multiple-angle capabilities, broad wavelength range, and opportunities of multilayer applications for adjusted ranges of high sensitivity. The chamber was prepared by 3D micromachining technology utilizing deep reactive ion etching of a silicon-on-insulator wafer and bonded to a polydimethylsiloxane microfluidic injection system resulting in a cell volume of approximately 50 μL. The mechanical stability of the 2 and 5 μm-thick membranes was tested using different “backbone” reinforcement structures. It was proved that the 5 μm-thick membranes are stable at lateral cell sizes of 5 mm by 20 mm. The cell provides good intensity and adjustment capabilities on the stage of a commercial mid-IR ellipsometer. The membrane configuration also provides optical access to the sensing interfaces at a broad range of incident angles, which is a significant advantage in many potential sensing structure configurations, such as plasmonic, multilayer, 2D, or metamaterial applications.
... Recently, there has been a rising interest in modifying conventional ellipsometric techniques to study vital biological processes. Kalas et al. investigated protein adsorption with the help of plasmonic ellipsometry with a Kretschmann-Raether geometry [225]. Similarly, Sohrabi and Hamidi utilised plasmonic ellipsometry to study brain activity [226]. ...
In recent years, several types of optical sensors have been probed for their aptitude in healthcare biosensing, making their applications in biomedical diagnostics a rapidly evolving subject. Optical sensors show versatility amongst different receptor types and even permit the integration of different detection mechanisms. Such conjugated sensing platforms facilitate the exploitation of their neoteric synergistic characteristics for sensor fabrication. This paper covers nearly 250 research articles since 2016 representing the emerging interest in rapid, reproducible and ultrasensitive assays in clinical analysis. Therefore, we present an elaborate review of biomedical diagnostics with the help of optical sensors working on varied principles such as surface plasmon resonance, localised surface plasmon resonance, evanescent wave fluorescence, bioluminescence and several others. These sensors are capable of investigating toxins, proteins, pathogens, disease biomarkers and whole cells in varied sensing media ranging from water to buffer to more complex environments such as serum, blood or urine. Hence, the recent trends discussed in this review hold enormous potential for the widespread use of optical sensors in early-stage disease prediction and point-of-care testing devices.
... After incubation at the room temperature for 30 min, the surfaces were taken out of the well, the extra medium on the diamond surface was carefully removed using a soft tissue and the surface was blown dry with nitrogen. The thickness of salt-protein layer on the diamond surface was measured by ellipsometry (EL Xe02C, DRE, Ratzeburg, Germany) [38] in three different positions per surface and three measurements per position. During ellipsometry measurements, an incidence angle of 50 and a 632 nm laser were used. ...
Diamond has been a popular material for a variety of biological applications due to its favorable chemical, optical, mechanical and biocompatible properties. While the lattice orientation of crystalline material is known to alter the interaction between solids and biological materials, the effect of diamond’s crystal orientation on biological applications is completely unknown. Here, we experimentally evaluate the influence of the crystal orientation by investigating the interaction between the <100>, <110> and <111> surfaces of the single crystal diamond with biomolecules, cell culture medium, mammalian cells and bacteria. We show that the crystal orientation significantly alters these biological interactions. Most surprising is the two orders of magnitude difference in the number of bacteria adhering on <111> surface compared to <100> surface when both the surfaces were maintained under the same condition. We also observe differences in how small biomolecules attach to the surfaces. Neurons or HeLa cells on the other hand do not have clear preferences for either of the surfaces. To explain the observed differences, we theoretically estimated the surface charge for these three low index diamond surfaces and followed by the surface composition analysis using x-ray photoelectron spectroscopy (XPS). We conclude that the differences in negative surface charge, atomic composition and functional groups of the different surface orientations lead to significant variations in how the single crystal diamond surface interacts with the studied biological entities.
... In most cases, enhancement of the sensitivity is related with increasing the electromagnetic field at the surface of a sensitive element. The detection limit value can be considerably reduced by using the systems with a high value of the ratio signalto-noise, namely: interferometry, ellipsometry or polarimetry [61][62][63]. Leading firms producing SPR-devices as well as scientific community improve both technology and design of SPR-devices to increase their sensitivity and accuracy in measurements. ...
Considered in this review are main directions of developing technology and construction of the available sensors based on surface plasmon resonance phenomenon to increase their sensitivity and accuracy of measurements. It has been shown that reducing roughness of the plasmon carrying layer in the sensor as well as application of an
additional covering dielectric layer with developed surface enables two-fold increase in the sensitivity due to the twice increased surface of interaction between the sensor and studied substance. The main technical way enabling to diminish surface roughness is thermal annealing, and the best result is usually reached for the annealing temperature
120 °С. In most cases, as a dielectric layer they use metal oxides Al2O3, TiO2, SiOx and ZnO, which allows attaining the detection limit in changes of the studied substance refraction index close to 1 • 10–9, what is one order better than that in available commercial analytic devices based on SPR phenomenon. Shown in the review are promising directions for development of SPR sensorics such as application of multilayer graphene coatings and polymer layers prepared by polymerization in high-frequency plasma of inert gas. Also, adduced in the paper are statistical data that show
the number of publications in scientific journals within this topic. This number underwent an exponential growth and to the end of 2015 was about six thousands, which is indicative of these investigations topicality and stimulates further studying the possibilities to improve and develop new analytical devices based on the SPR principle. In our opinion, further development of these sensors will be directed to increasing the selectivity, wear resistance of the sensitive element surface as well as to developing the methods for regeneration of receptors suitable for multiple using the sensitive elements.
Plasmonic AgAl/Si3N4 sensor layer structure was deposited on a fused silica glass slide by dual DC magnetron sputtering. The composition of the AgxAl1−x layer was laterally graded in which x linearly changes from x=0 to x=1 over a distance of 20 mm. The Si3N4 layer serves both as a resonator and a protective layer providing homogeneous chemical properties on top of the inhomogeneous AgAl layer. The structure was illuminated through a hemi-cylinder for variable-angle measurements in the Kretschmann-Raether configuration using a focused spot that enabled the change of x by moving it along the gradient of the composition. Optical properties of AgxAl1−x in the whole composition range were obtained. The positions of resonant peaks were shifted by changing the angle and the lateral position of the spot in a flow-cell configuration. The optical sensing performance of the bilayer system was investigated for x=0 and x=1. Based on the capabilities of ellipsometry limit of detection in refractive index unit values of ≈4−8⋅10−6 can be achieved in the resonant positions utilizing both p- and s-polarizations. Due to the flexible tunability of the resonant wavelengths by moving a focused spot, the above sensitivity is available in-situ, over the spectral range of 265-1504 nm.
Oxide-based materials and structures are becoming increasingly important in a wide range of practical fields including microelectronics, photonics, spintronics, power harvesting, and energy storage in addition to having environmental applications. This book provides readers with a review of the latest research and an overview of cutting-edge patents received in the field.
It covers a wide range of materials, techniques, and approaches that will be of interest to both established and early-career scientists in nanoscience and nanotechnology, surface and material science, and bioscience and bioengineering in addition to graduate students in these areas.
Features:
Contains the latest research and developments in this exciting and emerging field
Explores both the fundamentals and applications of the research
Covers a wide range of materials, techniques, and approaches.
https://www.taylorfrancis.com/books/oxide-based-materials-structures-rada-savkina-larysa-khomenkova/e/10.1201/9780429286728
In this study, the physicochemical characterization of lysozyme adsorbed on gold was investigated. Through the use of MP-SPR it was possible to establish that the orientation of molecules changes from side-on to between or end-on with increasing surface coverage. The data confirms that the process of adsorption is driven primarily by electrostatic interactions but also by hydrophobic forces. MP-SPR data was compared with the Random Sequential Adsorption model for a molecule with an ellipsoidal shape. Contact angle measurements showed that higher surface coverage also translates in more hydrophilic properties of obtained lysozyme layer. Comparison of CD and PM-IRRAS spectra in solution and adsorbed state respectively showed changes in the secondary structures of lysozyme. These changes are dependent on pH, but fundamentally they go in the direction of the increase of β-turn/random content with a simultaneous decrease in β-sheet fraction, which suggests that aggregation is not occurring. The combination of MP-SPR and QCM-D measurements allowed the estimation of the number of water molecules associated with the lysozymes films. It has been observed that hydration decreases from 70% in pH=4 to 30% in pH=11. This data indicates that hydration is driven mainly by the degree of protonation of lysozyme molecules.
Environmental monitoring of Ni is needed around the WHO threshold limit of 0.34 µM. This sensitivity target can usually only be met by time consuming and expensive laboratory measurements. There is a need for cheap field-applicable methods, even if it is only used for signaling the necessity of a more accurate laboratory investigation. In this work bio-engineered protein-based sensing layers were developed for Ni detection in water. The bacterial Ni-binding flagellin variants were fabricated using genetic engineering, and their applicability as Ni-sensitive biochip coatings was tested. Nanotubes of mutant flagellins were built by in vitro polymerization. A large surface density of the nanotubes on the sensor surface was achieved by covalent immobilization chemistry based on a dithiobis(succimidyl propionate) crosslinking method. The formation and density of the sensing layer was monitored and verified by spectroscopic ellipsometry and atomic force microscopy. Cyclic Voltammetry (CV) measurements revealed a Ni sensitivity below 1 µM. It was also shown that even after two months storage the used sensors can be regenerated and re-used by rinsing in 10 mM solution of ethylenediaminetetraacetic acid at room temperature.
Plasmon-enhanced in situ spectroscopic ellipsometry was realized using the Kretschmann geometry. A 10-μL flow cell was designed for multi-channel measurements using a semi-cylindrical lens. Dual-channel monitoring of the layer formation of different organic structures has been demonstrated on titania nanoparticle thin films supported by gold. Complex modeling capabilities as well as a sensitivity of ~40 pg/mm² with a time resolution of 1 s was achieved. The surface adsorption was enhanced by the titania nanoparticles due to the larger specific surface and nanoroughness, which is consistent with our previous results on titanate nanotubes.
A semi-cylindrical lens in Kretschmann geometry combined with a flow cell was designed for a commercial rotating compensator ellipsometer to perform internal reflection spectroscopic ellipsometry measurements, while allowing the use of multiple angles of incidence. A thin glass slide covered with a gold film was mounted between the half-cylindrical lens and a small-volume flow cell ensuring an improved sensitivity for protein adsorption experiments. The performance of the system was investigated depending on the angle of incidence, wavelength range and thickness of the gold films for surface plasmon resonance enhanced ellipsometric measurements, and a sensitivity increase was revealed compared to ellipsometric measurements with standard flow cells, depending on the measurement parameters and configuration. The sensitivity increase was demonstrated for fibrinogen adsorption.
The influence of substrate materials on protein adsorption was studied by spectroscopic ellipsometry (SE) and atomic force microscopy. For model proteins fibrinogen and flagellar filaments were chosen and their kinetics of adsorption, surface coverage and adsorbed amount on virgin and chemically activated SiO(2) and Ta(2)O(5) thin films were investigated. In case of flagellar filaments the SE data were analyzed with an effective medium model that accounted for the vertical density distribution of the adsorbed protein layer. Adsorption was measured in situ using flow cells with various fluid volume. Compared to commercially available cells, a flow cell with significantly smaller volume was constructed for cost-effective measurements. The development of the flow cell was supported by finite element fluid dynamics calculations.
Preface; 1. Introduction; 2. Theoretical foundations; 3. Propagation and
focusing of optical fields; 4. Resolution and localization; 5. Nanoscale
optical microscopy; 6. Near-field optical probes; 7. Probe-sample
distance control; 8. Optical interactions; 9. Quantum emitters; 10.
Dipole emission near planar interfaces; 11. Photonic crystals,
resonators, and cavity optomechanics; 12. Surface plasmons; 13. Optical
antennas; 14. Forces in confined fields; 15. Fluctuation-induced
interactions; 16. Theoretical methods in nano-optics; Appendices; Index.
A phase shifting optical waveguide interferometer is demonstrated for label-free evanescent wave biosensing in aqueous solutions. In the proposed configuration, the reference and measurement arms of the interferometer are combined inside an integrated optical Ta2O5 waveguide using an ion implanted grating. Biomolecules adsorbing on the waveguide surface shift the phase in the measurement arm, which is modulated at the same time by a periodically relaxing liquid crystal phase modulator. It is demonstrated that by analyzing the periodic intensity response at the end facet of the waveguide, the phase shifts in the measurement arm can be monitored in real-time with a precision of 10−4rad. The high phase resolution allows the detection of surface adsorbed molecule densities below 1pg/mm2 without using any labeling or on-chip referencing. The instrument performance is demonstrated by monitoring in situ protein adsorption and affinity binding of low molecular weight pure biotin to an immobilized avidin layer.
Ellipsometry is well-suited for bioadsorption studies and numerous reports, mainly using null ellipsometry, are found on this subject whereas investigations addressing structural properties of thin biolayers are few. Here two examples based on the use of spectroscopic ellipsometry (SE) on the latter are briefly discussed. In the first example, time evolution of thickness, spectral refractive index and surface mass density of a fibrinogen matrix forming on a silicon substrate are investigated with SE and a structural model of the protein matrix is discussed. In the second example a model dielectric function concept for protein monolayers is presented. The model allows parameterization of the optical properties which facilitates monitoring of temperature induced degradation of a protein layer. More recently, photonic structures in beetles have been studied with SE. It is shown here that full Mueller-matrix SE can resolve very complex nanostructures in scarab beetles, more specifically chiral structures causing reflected light to become circularly polarized.
A recently developed real time spectroscopic ellipsometer with an ultraviolet-extended spectral range (1.5–6.5 eV) has been applied to investigate the sputter deposition of BN films with high cBN content. Based on the optical contrast between the two phases (sp2 and sp3 bonded BN) above 4.5 eV, it has been possible to characterize the growth of these films using a two-layer isotropic optical model. In this model, the innermost layer represents the combined contribution from the sp2 bonded material (aBN and hBN) denoted collectively as hBN, whereas the outermost layer represents the contribution of the predominantly sp3 bonded material denoted as cBN. The BN films were grown on crystalline silicon substrates using two processes: (i) r.f. magnetron sputtering of a BN target with pulsed d.c. substrate biasing; and (ii) pulsed d.c. sputtering of a B4C target with r.f. substrate biasing. In both cases, the thickness evolution of the hBN and cBN layers as well as their dielectric functions over the extended spectral range have been determined. The cBN content deduced from the two-layer analysis is in good agreement with estimates from ex situ infrared transmission spectroscopy.
The quality of flagellin films in terms of thickness and homogeneity was investigated by spectroscopic ellipsometry. Flagellin films were prepared in three steps: silanization, glutaraldehyde activation and finally the coating with proteins. The process of film preparation was optimized by varying the duration of the silanization and by testing sticking on different substrates including Si wafer covered with different thickness of silicon-oxide and also covered with a thin film of tantallum pentoxide. Spectroscopic ellipsometry was applied to gain in-depth information on the film properties for the optimization of the immobilization. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
A variety of simple non-destructive techniques were investigated to suppress backside reflections from transparent glass and plastic substrates. Different “glassy” materials such as translucent adhesive tape, white glue, grease, paint, and modelling clay were investigated and found to work well for substrate materials with refractive indices in the range of 1.35 to 1.60, including materials such as fused silica, float glass, display glass, microscope slides, plastic sheets, etc. These back-surface suppression techniques are also useful in suppressing anisotropic effects from plastic substrates. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
In this study, we have reconstructed the statistical 3D structure of hundreds of nanometers thick surface immobilized flagellar filament protein layers in their native environment, in buffer solution. The protein deposition onto the surface activated Ta2O5 film was performed in a flow cell, and the immobilization process was followed by in situ spectroscopic ellipsometry. A multilayer optical model was developed, in that the protein layer was described by five effective medium sublayers. Applying this method, an in-depth analysis of the protein layer formation was performed. Based on the kinetics in the distribution of the surface mass density, the statistical properties of the filamentous film could be determined computationally as a function of the measurement time. It was also demonstrated that the 3D structure of the protein layer can be reconstructed based on the calculated in-depth mass density profile. The computational investigation revealed that the filaments can be classified into two individual groups in approximately equal ratio according to their orientation. In the first group the filaments are close to laying position, whereas in the second group they are in a standing position, resulting in a significantly denser sublayer close to the substrate than at a larger distance.Highlights► Flagellar filaments were immobilized onto Ta2O5 substrates in flow-cell. ► The surface was monitored in situ with spectroscopic ellipsometry. ► New optical model was developed for the characterization of the filamentous layers. ► The depth profile of protein mass density was determined. ► The statistical 3D structure of the filamentous layer was reconstructed.
Protein filaments composed of thousands of subunits are promising candidates as sensing elements in biosensors. In this work in situ spectroscopic ellipsometry is applied to monitor the surface immobilization of flagellar filaments. This study is the first step towards the development of layers of filamentous receptors for sensor applications.Surface activation is performed using silanization and a subsequent glutaraldehyde crosslinking. Structure of the flagellar filament layers immobilized on activated and non-activated Si wafer substrates is determined using a two-layer effective medium model that accounted for the vertical density distribution of flagellar filaments with lengths of 300–1500 nm bound to the surface. The formation of the first interface layer can be explained by the multipoint covalent attachment of the filaments, while the second layer is mainly composed of tail pinned filaments floating upwards with the free parts. As confirmed by atomic force microscopy, covalent immobilization resulted in an increased surface density compared to absorption.
The application of ellipsometry of the study of the adsorption behavior of proteins and synthetic macromolecules at the air-water interface has been investigated. It is shown that for macromolecules the amount adsorbed per unit area, Γ, as determined by ellipsometry, only has a well-defined physical meaning if the refractive-index increment remains constant up to high concentrations present in the adsorbed layer. It has been found experimentally that this conditioned is fulfilled for proteins. The ellipsometric Γ values of some protein agree satisfactorily with those obtained by two independent techniques has been used to investigate the adsorption from solution of κ-casein, bovine serum albumin, and polyvinyl alcohol. For bovine serum albumin, Γ reaches a plateau value of 2.9 mg/m2 for concentrations ≥ 0.05 wt%. The thickness of the adsorbed molecules. For κ-casein, Γ steadily increases with increasing centration and multilayers are formed. The technique provides interesting information on conformational changes in adsorbed macromolecules, on the rate of the process, and on the conditions under which these occur.
In this article, spectroscopic ellipsometry studies of plasmon resonances at metal-dielectric interfaces of thin films are reviewed. We show how ellipsometry provides valuable non-invasive amplitude and phase information from which one can determine the effective dielectric functions, and how these relate to the material nanostructure and define exactly the plasmonic characteristics of the system. There are three related plasmons that are observable using spectroscopic ellipsometry; volume plasmon resonances, surface plasmon polaritons and particle plasmon resonances. We demonstrate that the established method of exploiting surface plasmon polaritons for chemical and biological sensing may be enhanced using the ellipsometric phase information and provide a comprehensive theoretical basis for the technique. We show how the particle and volume plasmon resonances in the ellipsometric spectra of nanoparticle films are directly related to size, surface coverage and constituent dielectric functions of the nanoparticles. The regularly observed splitting of the particle plasmon resonance is theoretically described using modified effective medium theories within the framework of ellipsometry. We demonstrate the wealth of information available from real-time in situ spectroscopic ellipsometry measurements of metal film deposition, including the evolution of the plasmon resonances and percolation events. Finally, we discuss how generalized and Mueller matrix ellipsometry hold great potential for characterizing plasmonic metamaterials and sub-wavelength hole arrays. (C) 2011 Elsevier Ltd. All rights reserved.
Total internal reflection ellipsometry (TIRE) in spectroscopic mode in the wavelength range 400–1200 nm is employed in situ at a solid/liquid interface for investigation of protein adsorption on thin semitransparent gold films. In this configuration, the surface plasmon resonance phenomenon gives a large enhancement of the thin film sensitivity. Adsorption of a monolayer of the protein ferritin is monitored kinetically in situ and results in a change in the ellipsometric parameter Δ of more than 90° compared to 3° in similar ellipsometric measurements on gold substrates. This large sensitivity demonstrates a potential for sensor applications. The ferritin layer optical function is modeled with a Cauchy dispersion model resulting in a layer thickness of 9.2 nm, in good agreement with the dimension of the ferritin molecules. A transition layer between the protein film and the gold layer is necessary to introduce in the model to account for interactions between the protein layer and the gold film. The large sensitivity of TIRE for thin layers opens up a pathway to analyze in detail the structure of thin protein layers provided that a further development of the experimental setup and the model for the protein layer is carried out.
Over the past 5 years, more than 100 SPR biosensors for the detection of a variety of chemical and biological analytes were demonstrated. Most of these biosensors are based on prism coupling and angular or wavelength spectroscopy of surface plasmons. Commercial SPR systems have played an important role in the development of detection applications due to their increasing spread and the availability of special SPR platforms and kits dedicated to specific applications (e.g., Biacore Q for food analysis). Data collected in Tables 1-3 illustrate recent applications of SPR biosensors and achieved levels of performance. The performance figures should be compared with caution as performance of an SPR biosensor is a result of a multitude of factors (performance of optical platform, characteristics of the employed biorecognition element, suitability and degree of optimization of the immobilization method, detection format, and methodology), and thus low performance of one part of the biosensor (e.g., optical platform) can be compensated for by high performance of another component (e.g., biorecognition elements). Clearly, analytes implicated in food safety have received the most attention (Table 1). Bacterial pathogens such as E. coli and Salmonella were the most frequently targeted analytes. Detection limits below 102 bacteria/mL were reported. A great deal of research has been devoted to the development of SPR biosensors for other significant groups of analytes such as Staphylococcal enterotoxins (best demonstrated LODs < 1 ng/mL and antibiotics (best LODs < 1-10 ng/ mL depending on the substance). Several analytes have been detected also in complex food matrices. In the field of medical diagnostics (Table 2), the most attention has been paid to the development of SPR sensors for the detection of cancer markers (best LODs < 1-100 ng/mL) and antibodies (best LODs < 1-100 ng/mL). However, most of the detection experiments were performed in buffers rather than in clinical samples. The development of SPR biosensors for environmental monitoring (Table 3) has focused mainly on the detection of pesticides. The best LODs ranged from 1 to 100 pg/mL, depending on the analyte. Detection experiments were performed in buffers or real-world water samples. Conclusions: In the past, 5 years, SPR biosensor technology has made substantial advances in terms of both sensor hardware and biospecific coatings. SPR biosensors have been applied for the detection of a variety of chemical and biological analytes. We envision that the performance of SPR biosensor technology will continue to evolve and that advanced SPR sensor platforms combined with novel biospecific surfaces with high resistance to the nonspecific binding will lead to robust SPR biosensors enabling rapid, sensitive, and specific detection of chemical and biological analytes in complex samples in the field. These biosensors will benefit numerous important sectors such as medical diagnostics, environmental monitoring, and food safety and security. Abbreviations: ATR, attenuated total reflection; CCD, charge-coupled device; DNA, deoxyribonucleic acid; ELISA, enzyme-linked immunosorbent assay; LED, light-emitting diode; LOD, limit of detection; MALDI-TOF, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry; RIU, refractive index unit; RNA, ribonucleic acid; scFvs, single-chain antibody fragment; SAM, self-assembled monolayer; SP, surface plasmon; SPR, surface plasmon resonance; WDM, wavelength division multiplexing.
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