Far-field Directional Fluorescence Emission Enhancement Of Quantum Dots By Sharp Convex Gold Groove And Its Hybrid Structure

Biosensing is widely used in food testing,environmental monitoring,medicine and other fields and is closely related to human health.Therefore,improving the sensitivity of biosensing is of great significance to the life and health of human beings.By enhancing the far-field and ultra-far-field directional luminescence of the fluorescent material,the light trapping amount can be effectively increased,thereby improving the detection sensitivity.As a commonly used detection method in life sciences,fluorescence detection is characterized by real-time,high efficiency,intuitiveness,and sensitivity.Quantum dots are often used as probes in biomedical detection because of their unique advantages over other fluorescent materials.In biological detection using quantum dots as fluorescent markers,the luminescence effect of quantum dots has a direct effect on the sensitivity of biosensing.Therefore,it is important that sof great significance to enhance the detection and biosensing sensitivity of the directional fluorescence intensity in the far-field range of the enhanced quantum dots.Firstly,the grooved width of 4?m and the depth of 10?m were proposed for the gold-groove structure and two other wider gold grooves.The effects of quantum dot polarization and quantum dot position on directional emission were studied.The luminescence mechanism is due to the enhanced propagation of the waveguide resonance mode formed by the interaction of the scattered light emitted from the quantum dots and the reflected light within the gold channel to the far field.It has been found that the light intensity of the far field is higher than that of the gold groove structure with a wider gold groove structure and light coupling.When the quantum dots are located separately 3.5 ?m and 7.6 ?m above the bottom of the gold groove,this structure can achieve up to 17-fold and 6.6-fold far-field fluorescence enhancement compared to no structure.In addition,the influence of the thickness of the gold film and the effect of the structure in other wavelength bands was studied.The far-field fluorescence enhancement in the wide band can be achieved by ensuring that the bulge gold groove structure with a film thickness of 100 nm.Secondly,based on the above-mentioned gold cell,we propose a composite structure with a dielectric microcylinder.The ultra-far-field directional fluorescence emission intensity of quantum dot is studied as the size and refractive index of the dielectric microcylinder changes,the position of the quantum dot,and the amount of bio-solution in the gold groove.It was found that when the radius of the micro half-cylinders is 4~6?m and the refractive index is 1.5~1.7,the quantum dots located within 5.5?m above the grooves have obvious enhancement effect,and the enhancement factor is up to 87.37 times.The mechanism of far-field directional fluorescence emission enhancement is the combined effect of scattered light from quantum dots,waveguide resonance mode of gold channels,photonic jet,and lens effects.In addition,the fluorescent material in the solution can be greatly excited due to the optical photonic jet of the micro-cylinder and the waveguide mode in the gold groove.Finally,we propose a hybrid structure that a micro-half-cylindrical and cascading micro-half-cylindrical on a convex gold groove is proposed.The effect of size variation,refractive index change and convexity change of the dielectric microsemi-cylinders on the far-field and ultra-far-field directional fluorescence emission enhancement was studied.It was found that the hybrid structure can indeed enhance far-field directional fluorescence intensity,and when the refractive index range of the micro-half cylinder was 2.1~2.5,it works better.Comparing the fluorescence intensity of the single-and double-layer semi-cylindrical on gold groove,it was found that the double-layer semi-cylindrical on gold groove is more effective than the single-layer semi-cylindrical on gold groove.At the same time,the excitation process of a single-layer semi-cylindrical on gold groove was studied.It was found that the hybrid structure can effectively excite the fluorescent materials in the groove.In addition,it was found that the refractive index ratio(the ratio of the refractive index of the lens to that of the surrounding environment)of the microsphere/micro cylinder spray was not completely applicable to the micro hemisphere/micro half cylinder.