Efficient functionalization of the silicon nitride waveguide with bioreceptors, e.g. antibodies, is key to increase antigen binding activity in photonic sensors based on silicon nitride (SiN) waveguides. A bioreceptor coating technique using silica nanoparticles (NPs) to enhance the density of functionalized antibodies, by increasing the surface areas for biomolecule binding, is proposed. The detection of S100 Calcium-Binding Protein A6 (S100A6), a proposed cholangiocarcinoma marker, has been demonstrated using the SiN resonator sensor with 400nm thick waveguide, fabricated by low-cost 500 nm technology. The NPs were synthesized by silica condensation. Antibodies were attached to the NPs by 1-ethyl-3-(3- dimethyl aminopropyl)–carbodiimide (EDC)/ N-hydroxysuccinimide (NHS)-crosslinking. Then the NPs were coated on SiN sensor by N-terminal to N-terminal crosslinkers. It was found that the application of silica NPs coating showed increased sensor sensitivity at approximately 8.8 pm/(ng/ml) in optical resonant wavelength shift compared to 0.36 pm/(ng/ml) by our previous antibody coating technique using (3-Aminopropyl) triethoxysilane (APTES) silanization with EDC/NHS protein crosslink.
We developed an economical assembly for a silicon photonics resonator device including a device mount and lensed fiber holders for input and output fibers. The parts are fabricated by 3D printing technology using resin with digital light processing (DLP) technique and cured with UV light (405nm). The lensed fibers are aligned to the device waveguides using 6-axis aligner platform and their holders are affixed to the device mount by UV glue. Our in-house assembly module is able to firmly affix the fiber holders to the device mount and align the input and output lens fibers to the device spot size converter (SSC) of dimension 3.4 × 3.5 μm2. After alignment completion, the assembly can be detached from the aligner stage to be used in un-stabilized benchtop measurement system. The benchtop measurement system for the silicon photonic sensor device consists of a tunable laser, a polarizer, an optical power meter, and a container housing the device assembly, peristalsis pump and control circuits that was developed inhouse for microfluidics control having flow rate in the level of nanoliter/minute. In addition, a software has been developed for the measurement of the device resonant wavelength and wavelength shift due to sensor activity. We have demonstrated that the silicon photonics resonator that has been mounted on our assembly in the above measurement system showed acceptable performance by comparing the results with those obtained by mounting the device on stabilized fiber alignment platform. Thus, the 3D printed assembly may be used for silicon photonics device mount in early portable sensor prototype development.
In medical diagnostics there is an increasing demand for biosensors that can specifically detect biological analytes in a fluid. Especially label-free sensing, consistings of a transducer with biorecognition molecules immobilized on its surface without relying on fluorescent dye. In this paper we study the design and fabrication of a silicon nanowire photonic ring resonator and its feasibility as a biosensor. We have simulated and fabricated racetrack ring resonators which have a few tenths of micrometer gap, up to 0.5 μm between the input / output waveguides and the resonators. It is found that the devices can be designed with large Q factors. Sensitivity to biomaterial detection has been simulated for antibody (goat anti-mouse IgG) - antigen (mouse IgG) using 3-dimensional Finite Difference Time Domain technique. The simulated results show that the ring resonator has a response 15 nm resonance shift per refractive index unit. Antibody coating method is also discussed in this paper which can be applied to other antibody-antigen types.
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