Covalent Binding vs. Adsorption of Biomolecules on Silicon Nitride Planar Waveguides (original) (raw)
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Medical devices & sensors, 2020
The development of optical biosensors based on silicon dioxide or silicon nitride transducers requires the chemical activation of their surface to achieve stable, repeatable and homogeneous binding of biomolecules. In the present study, the chemical activation of silicon dioxide and silicon nitride surfaces with 3-aminopropyl-triethoxysilane (APTES) was optimized so as to enable the immobilization of biomolecules by adsorption or covalent bonding. Chemical activation was performed with either aqueous or organic solution of APTES and the surfaces were used to immobilize directly protein molecules by physical adsorption or further modified with glutaraldehyde to allow covalent binding of protein molecules. The protein immobilization capacity of the chemically activated silicon dioxide and silicon nitride surfaces was evaluated through incubation with mouse γ-globulins and reaction with a fluorescently labeled goat anti-mouse IgG antibody. By determining the surface fluorescence signal intensity, it was found that modification with 5% (v/v) APTES solution in ethanol followed by modification with glutaraldehyde provided 30% higher fluorescence signals than all the other protocols tested. In addition, this method provided the lower signal variation between different chips. To test the possible advantages of the chemical activation protocols for optical biosensing applications they were also applied to a label-free white light interference spectroscopy sensor and evaluated through a) real-time monitoring of the reaction between immobilized on the sensor surface mouse γ-globulins with an unlabeled goat antimouse IgG antibody and b) a non-competitive immunoassay for the determination of C-reactive protein. The results showed that in case of antibody, physical absorption provided marginally higher higher binding capacity to covalent bonding.
Biosensors and Bioelectronics, 2010
The selective introduction of functional groups on the surface of silicon nitride/silicon oxide nanostructures was studied. Chemical strategies based on organosilane, Si-H and N-H reactivities were assayed. Among these strategies, the use of glutaraldehyde to selectively immobilize biomolecules only on the silicon nitride part of the chip surface was the most effective for the covalent attachment of proteins, maintaining also their bioavailability. The biomolecule surface coverage results up to 80% and the modification is selective versus silicon oxide; the biomolecule attaching only to silicon nitride and leaving the silicon oxide area of the device unmodified. The effectiveness of our novel selective surface modification procedure is also supported by comparing experimental and numerical calculations of the optical performance of a label-free optical ring resonator based on Si 3 N 4 /SiO 2 slot-waveguides.
Talanta, 2020
The 3-aminopropyltriethoxysilane (APTES) is a common method for biomolecule immobilization on silicon and silicon derivatives such as silicon nitride (Si 3 N 4). However, there are many parameters which impact the efficiency of APTES modification such as APTES concentration and reaction time. Thus, various APTES concentrations (0.1%, 0.5%, 1%, 2%, 5%, and 10%) under different reaction times (15, 30, 60 and 120 min) were compared to achieve the optimal APTES modification condition which produced a thin and stable APTES layer on Si 3 N 4 surface. The modified surfaces were characterized by contact angle (CA) measurement, Fourier transform infrared (FTIR) spectroscopy and spectroscopic ellipsometry to determine the wetting property, chemical bonding composition and surface thickness, respectively. In addition, biotin was used as a model to determine the effectiveness of APTES modification condition by coupling with glutaraldehyde (GA). The Alexa Flour 488 conjugated streptavidin was performed to visualize the presence of biotin using fluorescence microscopy due to the specifically binding between biotin and streptavidin. The atomic force microscopy (AFM) was utilized to determine the surface topology which was an indicator to demonstrate the agglomeration of APTES molecule. Moreover, ion sensitive field effect transistor (ISFET) was employed as a biosensor model to demonstrate the effect between surface thickness and sensitivity of biosensor. The results show that the APTES thickness is directly correlated to the APTES concentration and reaction time. Since the importance parameter for ISFET measurement is the distance between biomolecule and sensing membrane of ISFET, the thicker APTES layer negatively impacts the sensitivity of ISFET based biosensor because of the ion shielding effect. Therefore, these results would be valuable information for development of Si 3 N 4 biosensor, especially ISFET based biosensor.
Characterization of anhydrous silanization and antibody immobilization on silicon dioxide surface
Formation of uniform and cluster free silane The thicker silane layer on the sensor surface alters the monolayer is one of the fundamental prerequisite for affinity mechanical properties of the biosensor. It also induces cantflever based biosensors. We report anhydrous silanization stresses on the sensor surface which may leads to difficulties protocol for uniform silane monolayer on silicon dioxide (SiO2) s n the s ensor suracewicayi ed o difficulTi surface using [3-(2-aminoethyl) aminopropyll-trimethoxysiane (APTES) and characterized by AFM, spectroscopic anticipate these problems silane monolayer with controlled ellipsometry and FTIR. Silanization coverage is controled by thickness on biosensor is essential. availability of surface water. The roughness of the resulting In the conventional protocol of aqueous phase silanized surface following our protocol is in the range of SiO2 silanization, the aminosilanes undergo hydrolysis and surface roughness. Silanized SiO2surface is used to immobilize polymerization in the bulk phase before depositing and human immunoglobulin (HlgG) on it. FITC tagged goat forming bonds with the silicon dioxide surface [1]. However, antihuman IgG is allowed to react with HIgG. The immobilized this results in the formation of polysilane networks prior to surface is further characterized using Fluorescent spectroscopy deposition. Thus polymerization of multifunctional silane and Fluorescent Microscope. Characterization results obtained molecules is observed both parallel and perpendicular to the from anhydrous silanization protocol are compared with the solfces leadtoforatoofiane me cule te conventional aqueous silanization protocol.
Analytical and Bioanalytical Chemistry, 2012
Methodology for the functionalization of siliconbased materials employed for the development of photonic label-free nanobiosensors is reported. The studied functionalization based on organosilane chemistry allowed the direct attachment of biomolecules in a single step, maintaining their bioavailability. Using this immobilization approach in probe microarrays, successful specific detection of bacterial DNA is achieved, reaching hybridization sensitivities of 10 pM. The utility of the immobilization approach for the functionalization of label-free nanobiosensors based on photonic crystals and ring resonators was demonstrated using bovine serum albumin (BSA)/anti-BSA as a model system.
Silicon-based biosensors for rapid detection of protein or nucleic acid targets
Clinical chemistry, 2001
We developed a silicon-based biosensor that generates visual, qualitative results or quantitative results for the detection of protein or nucleic acid targets in a multiplex format. Capture probes were immobilized either passively or covalently on the optically coated surface of the biosensor. Intermolecular interactions of the immobilized capture probe with specific target molecules were transduced into a molecular thin film. Thin films were generated by enzyme-catalyzed deposition in the vicinity of the surface-bound target. The increased thickness on the surface changed the apparent color of the biosensor by altering the interference pattern of reflected light. Cytokine detection was achieved in a 40-min multiplex assay. Detection limits were 4 ng/L for interleukin (IL)-6, 31 ng/L for IL1-beta, and 437 ng/L for interferon-gamma. In multianalyte experiments, cytokines were specifically detected with signal-to-noise ratios ranging from 15 to 80. With a modified optical surface, spe...
Analytica Chimica Acta, 2012
In this work we report the fabrication and characterization of a label-free impedimetric immunosensor based on a silicon nitride (Si 3 N 4 ) surface for the specific detection of human serum albumin (HSA) proteins. Silicon nitride provides several advantages compared with other materials commonly used, such as gold, and in particular in solid-state physics for electronic-based biosensors. However, few Si 3 N 4based biosensors have been developed; the lack of an efficient and direct protocol for the integration of biological elements with silicon-based substrates is still one of its the main drawbacks. Here, we use a direct functionalization method for the direct covalent binding of monoclonal anti-HSA antibodies on an aldehyde-functionalized Si-p/SiO 2 /Si 3 N 4 structure. This methodology, in contrast with most of the protocols reported in literature, requires less chemical reagents, it is less time-consuming and it does not need any chemical activation. The detection capability of the immunosensor was tested by performing nonfaradaic electrochemical impedance spectroscopy (EIS) measurements for the specific detection of HSA proteins. Protein concentrations within the linear range of 10 −13 -10 −7 M were detected, showing a sensitivity of 0.128 M −1 and a limit of detection of 10 −14 M. The specificity of the sensor was also addressed by studying the interferences with a similar protein, bovine serum albumin. The results obtained show that the antibodies were efficiently immobilized and the proteins detected specifically, thus, establishing the basis and the potential applicability of the developed silicon nitride-based immunosensor for the detection of proteins in real and more complex samples.
Feasibility Studies on Si-Based Biosensors
Sensors, 2009
The aim of this paper is to summarize the efforts carried out so far in the fabrication of Si-based biosensors by a team of researchers in Catania, Italy. This work was born as a collaboration between the Catania section of the Microelectronic and Microsystem Institute (IMM) of the CNR, the Surfaces and Interfaces laboratory (SUPERLAB) of the Consorzio Catania Ricerche and two departments at the University of Catania: the Biomedical Science and the Biological Chemistry and Molecular Biology Departments. The first goal of our study was the definition and optimization of an immobilization protocol capable of bonding the biological sensing element on a Si-based surface via covalent chemical bonds. We chose SiO 2 as the anchoring surface due to its biocompatibility and extensive presence in microelectronic devices. The immobilization protocol was tested and optimized, introducing a new step, oxide activation, using techniques compatible with microelectronic processing. The importance of the added step is described by the experimental results. We also tested different biological molecule concentrations in the immobilization solutions and the effects on the immobilized layer. Finally a MOS-like structure was designed and fabricated to test an electrical transduction OPEN ACCESS Sensors 2009, 9 3470 mechanism. The results obtained so far and the possible evolution of the research field are described in this review paper.
Biosensors, 2012
New silicon nitride coated optical gratings were tested by means of Optical Waveguide Lightmode Spectroscopy (OWLS). A thin layer of 10 nm of transparent silicon nitride was deposited on commercial optical gratings by means of sputtering. The quality of the layer was tested by x-ray photoelectron spectroscopy and atomic force microscopy. As a proof of concept, the sensors were successfully tested with OWLS by monitoring the concentration dependence on the detection of an antibody-protein pair. The potential of the Si 3 N 4 as functional layer in a real-time biosensor opens new ways for the integration of optical waveguides with microelectronics.
CMOS-compatible Si 3 N 4 Waveguides for Optical Biosensing
Procedia Engineering, 2015
We present a CMOS-compatible silicon nitride (Si 3 N 4) waveguide technology platform suitable for monolithic co-integration with optoelectronics in the visible and <1.1 μm near infrared wavelength region. With an optimized fabrication process employing low-temperature plasma enhanced chemical vapour deposition (PECVD) and reactive ion etching (RIE), propagation losses of 0.86 dB/cm were achieved at =850 nm for wire waveguides with a cross section of 600x250 nm². As an example of application we show Mach-Zehnder interferometer based label-free optical detection of the S-protein/S-peptide interaction. Moreover, we present experimental steps towards the realisation of multi-channel biosensors using spiral shaped waveguide structures ensuring a small form factor.