Fiber SPR Micro Sensor Modified With Nanostructures

Nowadays most continuous glucose monitoring systems,which are essential for diabetes treatment are based on implantable enzyme electrodes.However,enzyme electrode sensor has disadvantages of hypoglycemia information loss due to current signal drift caused by bioelectricity and irreversible glucose consumption due to enzyme catalysis,which could lead to inaccurate measurement.The fiber SPR sensor constructed a flexible and enzyme-free optical system to overcome such drawbacks.But the miniaturized fiber SPR sensor brings low sensitivity compared with prismbased SPR sensor.In order to solve this problem,although difficult,surface modification is necessary for sensitivity improvement.In this paper,we proposed a fiber SPR micro sensor modified with nanostructures for enhanced sensitivity.ultrasonic cavitation is first employed to roughen the gold surface on fiber SPR sensor.The gold nanostructure,which forms after ultrasonic process could stimulate LSPR effect.The graphene oxide(GO)is bounded onto the rough gold surface through layerby-layer method.And we proposed a novel liquid transfer method to transfer CVD single-layer graphene onto the rough gold surface.The gold nanostructure and two types of 2D materials improve the sensor sensitivity significantly.This work could be divided into following parts.(1)The theory of fiber SPR sensor design: we elaborate the theories of SPR,LSPR and ultrasonic cavitation,ultrasonic process mechanism to gold surface,mechanism of sensitivity enhancement by 2D material,etc.(2)Design and fabrication of fiber SPR sensor: we describe the structure of fiber SPR sensor and optimize three main parameters of the sensor through simulation.We complete the coating process utilizing the thermal evaporation and the encapsulation of fiber SPR sensor has been carried out.(3)The modification method of nanostructure: ultrasonic cavitation is first employed to roughen the gold surface on fiber SPR sensor for construction of gold nanostructures.Binding GO through layer-by-layer method and transferring CVD single-layer graphene by liquid transfer method.(4)Performance test of fiber SPR sensor: we build the test system and the optimization of ultrasonic time,number of GO layer and number of graphene have been conducted experimentally.The result shows that the sensitivity of sensor without any process,sensor with 15 min ultrasonic process and 3-layer GO and sensor with 15 min ultrasonic process and 2-layer graphene are 873nm/RIU,2706nm/RIU and 3113nm/RIU respectively.The three relative coefficients are 0.93,0.86 and 0.98.The two structures of fiber SPR sensor bring 3 fold and 3.6 fold increases in sensitivity respectively.The electro-optical properties of continuous membrane-like graphene is better than the discrete flaky.Thus graphene shows a greater degree of sensitivity improvement than GO.