Research On Biological Sensing Based On Fano Resonance Terahertz Metasurfaces

The terahertz(THz)wave has very attractive characteristics for biosensing applications,due to some interesting features such as being a non-ionizing radiation,very sensitive to weak interactions.However,a fundamental drawback is its relatively long wavelength(10-1000 μm)which makes it blind to small features,hindering seriously biological sensing.Recently,new ways to overcome this limitation have become possible thanks to the advent of metasurfaces.These artificial ultra-thin metasurfaces are usually made of periodic metallic resonators and whose electromagnetic response can be controlled at will by design.By creating fine details comparable to the size of the biomolecules being test,this design allows the metasurfaces to surpass the restrictions of classical THz spectroscopy.The strong electromagnetic field concentration near nano structures at resonance makes them highly sensitive to tiny variations in the nearby environment,allowing for an enhanced detection more accurate than classical THz spectroscopy.Additionally,metasurfaces based on Fano resonance structures can excite asymmetric resonances to present sharp narrow spectrum with high quality(Q)factors,and be highly sensitive to the variation of surrounding dielectric environment.Based on above reasons,we proposed a terahertz metasurface biosensors based on Fano asymmetric split ring resonators and used to detect the protein A/G,protein A/G+IgG.The details of the paper are listed as follows:A new terahertz metasurfaces biosensor based on Fano resonances fabricated on 25 μm flexible polyimide substrate was proposed and its unit cell is composed of asymmetric split ring arrayed periodically.First,we study the physical mechanism of Fano resonances.Secondly,we use numerical simulation software,the structural parameters of the metasurfaces are optimized and studied the characteristics of transmission spectrum in TE and TM modes,respectively.Simulation results show that two resonance dips are located near 0.81 THz and 1.13 THz,respectively.The two resonance dips of Q factor reached 5.67 and 3.45,the refractive index sensitivity(S)are 160 GHz/RIU and 240 GHz/RIU,and the value of FOM(figure of merit)are 0.91 and 0.83,respectively.Correspondingly,we fabricated and measured the proposed structure.The experimental results are consistent with the simulation results.Finally,we studied the sensing of protein A/G and IgG with THz metasurface.In our experiments,the resonance dips shifts of 8.9 GHz and 11.7 GHz,17.6 GHz and 52.9 GHz toward low frequency were observed,respectively.The results illustrated that our metsurface biosensors have high sensitivity and label-free detection for proteins,which provides new feasible way of biosensing in terahertz domain.