Ultrasensitive Surface Plasmon Resonance Biosensors Based On Two-dimensional Materials

In recent years,the application of the theory of surface plasmon resonance?SPR?in optical studies has caused widespread concern,such as the food safety testing,environmental monitoring,medical diagnosis,biological engineering and so on.Especially the applications of SPR in the biosensing technology have attracted wide attentions and researches.Surface plasmon polariton?SPP?exists on the surface of metals,which is sensitive to the change in the refractive index of sensing medium.A small change in the refractive index of sensing medium near the interface can result in a significant change in the characteristics of the reflectance curve.The conventional SPR sensors based on Kretschmann structure are designed by coating the gold?Au?thin film on the prisms to excite surface plasmon waves?SPWs?.However,the sensitivity of the conventional SPR biosensor has a deficiency with low sensitivity,and the biosensor with a higher sensitivity is demanded.Since entering the 21 st century,the material science has entered a new stage of rapid development,many new materials have been found and aroused great interest,many advanced and practical two-dimensional?2D?materials have been found and studied to have an application,such as graphene,TMDCs,black phosphorus and so on.With the introduction and the application of these two-dimensional materials,the development of SPR sensor has a good prospect.In this paper,we mainly study the enhancement of sensitivity of two-dimensional materials in SPR biosensors.A total of six SPR biosensor chips based on two-dimensional materials were designed.The innovations are as follows:?1?An ultra-high sensitivity SPR sensor based on the graphene-aluminum?Al?-graphene sandwich-like structure is proposed.It is found that our proposed graphene optical sensor is 3.4 times more sensitive than the Al-based sensor without the graphene layers.Especially,the sensitivity can be enhanced marked by increasing the number of graphene layers.The related researches published on “Journal of Applied Physics”.?2?A novel long-range surface plasmon with graphene is proposed to enhance the sensitivity and detection accuracy?DA?of biosensor.Comparing to the conventional long-range SPR?LRSPR?structure with Au,the coating of the metal surface with graphene is employed to increase the biomolecules adsorption,prevent oxidation,and enhance the sensitivity and DA.Further,we demonstrated that the sensitivity can has nearly tenfold improvement with a huge increasing DA in the proposed LRSPR biosensor compared with the SPR biosensor.Finally,we discuss the influence of the refractive index of sensing medium on the LRSPR biosensor,and find that the sensitivity is changing with the refractive index of sensing medium and an optimal sensitivity can be obtain at a suitable refractive index.The related researches published on “IEEE Photonics Journal”.?3?An ultrasensitive biosensor based on hybrid structure,composed of long-range SPP?LRSPP?and dielectric planar waveguide?PWG?mode,is proposed.Both PWG and LRSPP modes have strong resonances to form the strong coupling between two modes,and the two modes can couple to enhance sensitivity of sensors.The highest imaging sensitivity with 2264 RIU-1 and 3619 RIU-1 have been realized in the proposed sensor based on Au and Al-monolayer graphene,and it is nearly 1.2 times and 1.9 times larger than the sensitivity?1910 RIU-1?of the conventional LRSPR sensor.Moreover,it is demonstrated that the PWG-coupled LRSPP biosensor is applicable the sensing medium with refractive index in the vicinity of 1.34.The related researches published on “Photonics Research”.?4?A SPR biosensor based on MoS₂/graphene-Al hybrid structure is proposed to enhance the sensitivity.The sensitivity of the proposed biosensor is enhanced by using three methods.Firstly,prisms of different refractive index have been discussed and it is found that sensitivity can be enhanced by using a low refractive index prism.Secondly,the influence of the thickness of the air layer on the sensitivity is analyzed and the optimal thickness of air is obtained.Finally,the sensitivity improvement and mechanism by using molybdenum disulfide?MoS₂?-graphene hybrid structure is revealed.The maximum sensitivity 190.83 o/RIU is obtained with six layers of MoS₂ coating on both surfaces of Al thin film.The related researches published on “Journal of Lightwave Technology”.?5?A SPR biosensor based on guided-wave SPR?GWSPR?is proposed.Compared with SPR biosensor,GWSPR biosensor has a higher sensitivity.In order to further enhance the sensitivity of the GWSPR biosensor,the MoS₂-graphene hybrid structure is proposed to cover on the surface of the thin silicon film.It is demonstrated that the sensitivity of the proposed biosensor configuration can be doubled by using optimized MoS₂-graphene hybrid structure.By analyzing the electric field distributions with the proposed GWSPR biosensor,it is shown that the electric field intensity has a dramatic change with a slight change in refractive index of sensing medium,and it also means that the biosensor is sensitive to detect the analytes.Moreover,the proposed GWSPR biosensor has a wide detection range of refractive index of sensing medium,and the sensitivity is increased with the refractive index of sensing medium increasing.The related researches published on “Plasmonics”.?6?The heterostructure of two-dimensional materials are promising and useful in the field of SPR biosensors.To enhance the sensitivity,we design a novel SPR biochemical sensor by using heterostructures of few-layer black phosphorus?BP?and graphene/transition metal dichalcogenides?TMDCs?.The SPR biosensor based on the different heterostructures of BP and graphene/TMDCs are analyzed,and the highest sensitivity with 279 °/RIU for the heterostructure of BP and bilayer WSe2 is obtained.The maximum sensitivity of our proposed SPR biosensor is about 2.4 times of the conventional biosensor.The related researches published on “Sensors and Actuators B: chemical”.