Ultrasensitive metadevices for biosensing

• Main Author: Xiao, Shuqi
• Other Authors: Luo Yu
• Format: Thesis-Master by Coursework
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Electrical and electronic engineering::Optics, optoelectronics, photonics
• Online Access: https://hdl.handle.net/10356/150843
• Institution: Nanyang Technological University

Cheap biosensors for fast, real-time probes of biological analytes, are highly required in many new healthcare programmes. Surface plasmonic platforms are suitable for low-cost real-time diagnostic devices due to high sensitivity for the variation of dielectric functions of molecules at the interface (caused by the absorption) and the possibility for the integration into the biosensing systems. However, major barriers remain in building point-of-care plasmonic devices due to absorption losses inherent in metals at optical band, specificity of analyte identification, the difficulty in placing the sample molecules at the hot-spots on the devices. Moreover, traditional optical biosensors normally use resonance shift to detect the variations in refractive index of different analytes rather than identify the molecules themselves. Detecting the molecule’s vibrational modes is one way to solve this problem. Starting with the principles, a metadevice is designed and its structure is introduced in the dissertation. The principles mainly include the surface plasmon polaritons and modulation of graphene by Fermi level. Surface plasmon polaritons have the outstanding capability to enhance and confine large electromagnetic field, which can dramatically increase the interaction between the light and the molecules and improve detection sensitivity of the molecule vibrational fingerprints. Graphene is a special inorganic material and can be consider as a conductor like metal. Most importantly, its permittivity can be modulated by changing Fermi level, which provide the possible to tune the peak of surface plasmon polariton spectra. The configuration of this metadevice consists of a silica substrate, a gold grating and a monolayer graphene acting as a conductor to sustain the surface plasmon polaritons. It can be employed as an ultrasensitive sensor to detect molecules spreading on it. By tuning the Fermi energy of graphene, the different spectrums are recorded and analyzed in order to identify the special molecule fingerprint according to their dielectric function. Relying on the structure, simulation has been done in Finite-difference Time-domain Simulation Software and the simulation result is collected and processed in Matlab and the simulation reveals good result of the metadevice. Utilizing 8 nm thick goat anti mouse immunoglobulin G and recombinant protein A/G as the sensing analyte, the simulation has showed a good result. The wavelengths at the extreme values can be considered as the characteristic absorption peaks measured by the metadevice. The deviation is less than 0.015 μm from the characteristic absorption peak at the wavelengths of 6.000 μm and 6.523 μm. This indicates that the structure of metadevice can well distinguish the protein or even some other substances.