Biosensor Based On Plasmonic Mach-Zehnder Interferometer With Metallic Gratings

Several great breakthroughs have been made in the field of traditional optical sensing system recently.The performance and integration of the systemimprove constantly as well as the cost decreasing.But in the field of biosensor,the traditional optical sensing technology demonstrates the disadvantages of high cost.And large size,and it is facing many difficulties in the optical integration.Biosensors have a wide range of applications in clinical detection,water quality monitoring and virus detection.Biosensors with the characteristics such as low cost,small size,high sensitivity,and fast response are the aim of many researchers.At present,the biosensing technology has reached several achievements.Among them,surface plasmon polaritons(SPPs),as a new generation of sensing technology,can realize photonic components in a true sense and overcome the diffraction limit of light.The potential for development has attracted the attention of many scholars.Because SPPs waves are very sensitive to changes in the refractive index and dielectric properties around them,based on these properties,nano plasmon structures have become a new choice for biosensor devices.The typical SPPs biosensing technology is to couple the incident electromagnetic waves to the metal-dielectric interface to form the SPPS by a prism,that is called kretschmann structure.This method has relatively high sensitivity,but it is hard to integrate.An alternative to the prism is metal nano structure which can excite the SPPs and be integrated on a chip.Even if the nano plasmon biosensor overcomes the defects of large size and difficult to integrate,in order to be practically applied in the field of biosensing,a big breakthrough is needed in sensitivity,such as the one proposed by Hao Jiang et al.Periodic nano plasmon sensor with a sensitivityof 637.3nm/RIU,Saeed Mirzanejhad proposed a plasma-based Mach-Zehnder interferometric sensor with a sensitivity of 468nm/RIU.The sensitivity is hard to reach 92000nm/RIU(the size is too large and lacks the possibility of integration with electronic chips).In order to improve the sensing performance of biosensors,researchers have proposed that the waveguide optimization is a key task to improve its sensitivity,such as Hybrid plasma waveguide(HP),silicon-on-insulator(SOI)waveguide,the mental strip loaded horizontal slot hybrid plasmonic waveguide,and plasma slit waveguide.Up to now,there have been a variety of nano biosensors,such as sub-wavelength wave guide sensors,MachZehnder interferometric sensors.In order to further improve the sensing performance of the biosensor,a new nano plasmon sensing structure is proposed by combining the nano plasmom structure and the interferometric plasmon sensing structure.Because interferometric sensors rely on the interference of light,they do not need an overly complicated sensing structure.By adjusting the size of the sensor structure,the sensing performance can be effectively improved,and it has become an effective prototype to sensing technology.In this paper,a kind of biosensor combining Mach-Zehnder interferometer and periodically arranged nano plasmon structure is adopted.Due to the simple structure and lower cost of the Mach-Zehnder interferometric sensor,it has the advantages of the both structures.This sensor comprises a silichn nanowire and two different silver nanoparaicle chains deposed on the silica substrate.The gaps between the chains and the nanowire act as the two arms of the MZI,this kind of slot waveguide can limit the optical mode within the nano slit due to high index contrast or surface plasmon enhancemen,and by adjusting the size of the periodic silver nanoparticle chains on both sides to achieve the effect of optimizing the sensing performance.This sensor can effectively reduce the transmission loss of the sensor and improve the sensing performance.