Enhanced Fluorescence Emission In Hybrid Metal-dielectric Structure

Fluorescence detection can be widely used in many fields,such as biological sensing,environmental detection,and chemical analysis due to the advantages of simple operation,high sensitivity,and safe.However,with the development of fluorescence technology,the sensitivity of fluorescence is becoming higher and higher.The sensitivity of fluorescence is related to the intensity of fluorescence,and the enhancement of fluorescence intensity can be achieved by using a micro/nano structure.Among them,fluorescence enhancement in the near field range has been extensively studied.However,in the actual in vitro detection,the fluorescent substance is far away from the structure.so it is significant to study the fluorescence enhancement when the fluorescent substance is far away from the structure.Based on the above analysis,a semicircular tube with fishtail-shaped lens hybrid structure is proposed.The effect of fluorescence intensity are investigated when the inner diameter and thickness of the semicircular tube,the angle andthickness of the fishtail lens,refractive index of semicircular tube and fishtail lens are changed.The results showed that the inner diameter and thickness of the semicircular tube is 2.5μm,0.5μm,and the thickness and angle of the fishtail-shaped lens is 0.5μm,30°,respectively,the fluorescence enhancement effect is higher.Besides,the fluorescence enhancement of our structure is up to11 times and 3.6 times compared with bare glass and the semicircular tube structure.Following,we further explored the effect of structural shape changes on fluorescence intensity.In addition,based on the previous structure,we designed the number of fishtail lenses to three.Changing the position,thickness,angle of the three fishtail lenses,we can observe the change on fluorescence.When the angle between the three lenses is 30°,thickness of three lenses are 0.5μm,the intermediate lens is 30° and the other two lenses angle are 10°,the fluorescence is significantly enhanced.Finally,an Ag-Si hybrid structure is designed to enhanced fluorescence.According to the comparison of Ag,Si,Si-Ag and glass structure,the designed structure can achieve fluorescence enhancement.The Ag-Si structure is discussed in the excitation and emission processes.In the emission process,the effect of the fluorescence intensity is discussed when change the thickness of the silver and silicon pillars in the structure,the width of the slit,and the position of the quantum dots.When the thickness of the silver pillar and the silicon pillar are both 0.5μm and the width of the slit is 2μm,the Ag-Si structure can achievefluorescence enhancement compared with the glass.In addition,in the excitation process,the fluorescence intensity of Ag-Si structure is higher than bare glass structure and the electric field distribution of Ag-Si structure is more uniform in the slit between the two pillars than the Ag and Si-Ag structures.So,fluorescence enhancement can be achieved and the detection of molecular motion behavior is more accurate in Ag-Si structure.