Study Of Microlens Array For Polymer Microfluidic Chip Fluorescence Enhancement

Microfluidic system based on laser induced fluorescence(LIF)detection have been widely used in the field of biochemistry,such as clinical diagnosis,environment inspection and biological warfare agents.Because of the little amount of sample in the systems,the induced fluorescence is weak and lower sensitivity.In order to enhance the fluorescence detection system strength and sensitivity of detection,a microfluidic chip integrated microlens array(MLA)was designed and fabricated.The main contents are as follows:(1)Based on principle of Fermat and the classical geometrical optics theory,double spherical micro lens in a heterogeneous medium of object-image relations was derived.On the basis of the double spherical micro lens of object-image relations,a curvature radius of a micro-lens approaching infinity,flat convex microlenses object-image relation is deduced,and then the flat convex micro lens focal length was deduced.In addition,the design method of photoresist microlens was introduced and shape shifts was analyzed before and after photoresist reflow.(2)Different size of PDMS micro lens array was designed and fabricated and the forming mechanism of the photoresist microlens was studied.Firstly,using photolithography and thermal reflow technology,photoresist microlens array was produced on the silicon substrate.Secondly,PDMS micro lens array mold was abtained by the casting technology.Finally,a PDMS cover plate with MLA was produced using soft-lithography technology.Reflow process of the photoresist cylindrical was studied.The height of the photoresist cylinder rises with the increase of temperature between 120 ? and 150 ?,and its shape transforms gradually volcano shape into sphere shape.The bottom diameter photoresist decreases by 5% after reflow.In addition,the relationship between the photoresist cylindrical deep width ratio and photoresist microlens' osculation angle was studied.The osculation angle rises as the photoresist cylindrical deep width ratio increases.However,when deep width ratio is less than 0.04,the photoresist microlens can not be formed.(3)A PDMS microfluidic chips integrated microlens array was fabricated.The performance of the proposed lens was examined with FITC.Fluorescence images was abtained by fluorescence convert microscopy,and fluorescence intensity was acquired using MATLAB software.The relationship between the fluorescence intensity and the concentration of FITC was studied.Result shows that the fluorescence intensity rise with the increase of FITC concentration.However,when the concentration is higher than 10 ?mol/L,the fluorescence intensity remians unchanged.The fluorescence intensity and sensitivity of detection with the microlens was approximately 2.2 times higher than those without the microlens.Fill factor's influence on fluorescence intensity was explored under the condition of same microlens.The fluorescence intensity increased with the increase of the fill factor.