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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.

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... 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. ...
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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. ...
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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.
... 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. ...
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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.
... 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. ...
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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.
... 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. ...
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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.
... 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]. ...
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... 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. ...
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... 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. ...
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... 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. ...
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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.
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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.
Article
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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