Evanescent field response to immunoassay layer thickness on planar waveguides (original) (raw)
Related papers
2019
Optical Waveguide Lightmode Spectroscopy (OWLS) is widely applied to monitor protein adsorption, polymer self-assembly, and living cells on the surface of the sensor in a label-free manner. Typically, to determine the optogeometrical parameters of the analyte layer (adlayer), the homogeneous and isotropic thin adlayer model is used to analyze the recorded OWLS data. However, in most practical situations, the analyte layer is neither homogeneous nor isotropic. Therefore, the measurement with two waveguide modes and the applied model cannot supply enough information about the parameters of the possible adlayer inhomogeneity and anisotropy. Only the so-called quasihomogeneous adlayer refractive index, layer thickness, and surface mass can be determined. In the present work, we construct an inhomogeneous adlayer model. In our model, the adlayer covers the waveguide surface only partially and it has a given refractive index profile perpendicular to the surface of the sensor. Using analytical and numerical model calculations, the step-index and exponential refractive index profiles are investigated with varying surface coverages from 0 to 100%. The relevant equations are summarized and three typically employed waveguide sensor structures are studied in detail. We predict the errors in the calculated optogeometrical parameters of the adlayer by simulating the OWLS measurement on an assumed inhomogeneous adlayer. We found that the surface coverage has negligible influence on the calculated refractive index below film thicknesses of 5 nm; the calculated refractive index is close to the refractive index of the adlayer islands. But the determined quasihomogeneous adlayer refractive index and surface mass are always underrated; the calculated quasihomogeneous thickness is heavily influenced by the surface coverage. Depending on the refractive index profile, waveguide geometry, and surface coverage, the thickness obtained from the homogeneous and isotropic modeling can even take negative and largely overestimated values, too. Therefore, experimentally obtained unrealistic adlayer values, which were dismissed previously, might be important indicators of layer structure.
Immunosensing using a metal clad leaky waveguide biosensor for clinical diagnosis
Sensors and Actuators B: Chemical, 2012
The optical detection technologies have been used in biosensors for the highly sensitive, real-time and label-free detection of biomolecules. In this report, a metal clad leaky waveguide (MCLW) was used as an immunosensing tools. We optimized the structure of the sensor chip for highly sensitive detection, followed by fabrication of the MCLW sensor chips and construction of a detection system for immunosensing. Titanium and SiO 2 films were deposited onto a BK7 substrate using an E-beam evaporator and the thickness of the films was 9 nm and 347 nm, respectively. The sensing response of the system to the bulk refractive index was calibrated using various concentrations of a glycerol solution. As a result, the MCLW sensor system was able to detect a change of ∼3.8 × 10 −6 RIU in the refractive index of the ambient solution. In addition, immunosensing was achieved using the MCLW sensor for an antigen-antibody reaction in real time. The biotin-labeled antibody of human interleukin 5 (hIL5) was immobilized on the sensor surface containing modified with streptavidin. The hIL5 in a bio-solution was quantitatively analyzed in real time using the MCLW sensor system.
Biomolecular sensors utilizing waveguide modes excited by evanescent fields
Journal of Microscopy, 2008
Properties of evanescent-field-coupled waveguide-mode sensors consisting of a multi-layer structure made of a SiO 2 waveguide, a thin metal layer (Au, Cu, W or Ti), and a high refractive index glass substrate illuminated under the Kretschmann configuration have been theoretically and experimentally investigated. In all cases, reflectivity changes attributed to streptavidin combining to biotinyl groups were observed in close spectral vicinity of the waveguide resonances. The sensors with the Au and the Cu layers show superior sensitivity as compared to those with the W and the Ti layers, whereas the W and Ti layers show better thermal and chemical stability. The results indicate that the materials of thin metal layers should be chosen in accordance with the purpose of sensors and/or environment in which the sensors are used.
Performance of a highly sensitive optical waveguide Mach-Zehnder interferometer immunosensor
Sensors and Actuators B-chemical - SENSOR ACTUATOR B-CHEM, 1993
We describe a highly sensitive sensor which uses the evanescent field of a reusable planar optical waveguide as the sensing element. The waveguide used is optimized to obtain a steep dependence of the propagation velocity on the refractive-index profile near the surface. The adsorption of a layer of proteins thus results in a phase change, which is measured interferometrically using a Mach-Zehnder interferometer set-up. The stability of the interferometer is such that phase changes = (1 × 10-2)2pi per hour can be measured. Immunoreactions have been monitored down to concentrations of 5 × 10-11 M of a 40 kDa protein.
Modification of the surface of integrated optical wave-guide sensors for immunosensor applications
Fresenius' Journal of Analytical Chemistry, 2001
Methods have been developed which enable attachment amino and epoxy groups to the surface of integrated optical wave-guide sensors for immunosensor applications. The SiO 2 -TiO 2 surfaces were modified by use of the trifunctional silane reagents γ-aminopropyltriethoxysilane (APTS) and γ-glycidoxypropyltrimethoxysilane (GOPS) in organic and/or in inorganic phases. Silanization methods were optimized taking into consideration the concentration of silane reagent used and the temperature and time of reaction. To evaluate the layers formed, immobilization experiments were undertaken on the modified surfaces using the bovine serum albumin (BSA)-anti-BSA IgG antibody model molecule pair. The regenerability of the sensitized surfaces was also studied.
The critical sensor: a new type of evanescent wave immunosensor
Biosensors and Bioelectronics, 1996
A new planar waveguide immunosensor has been developed in which adsorption at a surface, changing the refractive index contrast, is measured. In this "critical" sensor the change in the effective refractive index contrast is transducted to a shift of the critical reflection angle. The sensor's response after a specific binding of antigens to antibodies is discussed theoretically. In addition, an experimental sensitivity evaluation on the basis of several immunosensing experiments is presented. The obtained lower detection limit is 2 × 10 -2 nm in adlayer growth, equivalent to 12 pg/mm z of analyte coverage. This sensitivity is comparable to the performance of the surface plasmon resonance sensors or the grating coupler sensors. However, the "critical" sensor has some advantages. These are mainly the ease of fabrication and adjustment prior to a measurement, and the fact that for an experiment no metal layer has to be used.
Sensors, 2020
In this paper, a compact, integrated, semiconductor-clad strip waveguide label-free biosensor is proposed and analyzed. The device is based on CMOS-compatible materials such as amorphous-Si and silicon oxynitride. The optical sensor performance has been modeled by a three-dimensional beam propagation method. The simulations indicate that a 20-µm-long device can exhibit a surface limit of detection of 3 ng/cm 2 for avidin molecules in aqueous solution. The sensor performance compares well to those displayed by other photonic biosensors with much larger footprints. The fabrication tolerances have been also studied in order to analyze the feasibility of the practical implementation of the biosensor.
Optimizing the Limit of Detection of Waveguide-Based Interferometric Biosensor Devices
Sensors, 2019
Waveguide-based photonic sensors provide a unique combination of high sensitivity, compact size and label-free, multiplexed operation. Interferometric configurations furthermore enable a simple, fixed-wavelength read-out making them particularly suitable for low-cost diagnostic and monitoring devices. Their limit of detection, i.e., the lowest analyte concentration that can be reliably observed, mainly depends on the sensors response to small refractive index changes, and the noise in the read-out system. While enhancements in the sensors response have been extensively studied, noise optimization has received much less attention. Here we show that order-of-magnitude enhancements in the limit of detection can be achieved through systematic noise reduction, and demonstrate a limit of detection of ∼ 10 - 8 RIU with a silicon nitride sensor operating at telecom wavelengths.
The realization of an integrated Mach-Zehnder waveguide immunosensor in silicon technology
Sensors and Actuators B: Chemical, 1997
We describe the realization of a symmetric integrated channel waveguide Mach-Zehnder sensor which uses the evanescent field to detect small refractive-index changes (2~n~n ~ 1 x 10 -4) near the guiding-layer surface. This guiding layer consists of ridge structures with a height of 3 nm and a width of 4 gm made in SisN4. This layer has a thickness of I00 nm. The sensor device has been tested with glucose solutions of different bulk refractive indices. Results of a slab-model calculation are in good agreement with obtained experimental results. The feasibility of applying this sensor for immunosensing, detecting directly the binding of antigen to an antibody receptor surface, is shown with antibody-antigen binding experiments. © 1997 Elsevier Science S.A.