Fabrication And Electrochemical Sensing Application Of Photolithographic Microarray Electrode

The electrochemical biosensor is composed of an identification element,an electrode and a signal amplifying device.As a transducer,the electrode has an important influence on the performance of the sensor.However,the conventional planar electrodes with small specific surface area and a low surface roughness are disadvantageous for the preparation of highly sensitive sensors.There are two methods for these problems by constructing a three-dimensional sensing coating on the electrode and directly preparing a three-dimensional electrode.The former method often has problems such as poor reproducibility,complicated process and poor adhesion,which is difficult to achieve industrial production.In comparison,the way to construct a three-dimensional electrode is more reproducible and popular.The type of three-dimensional structure is very important for the preparation of high-performance sensors.In a variety of micro-nano structures,microarray structures have attracted wide attention because of their controllability,diversification of preparation methods,and small batch differences.The preparation method usually includes photolithography,electrophoretic deposition,hydrothermal method,and so on.Among them,photolithography technology is the most effective preparation method at present because it has a better industrial base,complete industrial chain,and has great potential for commercialization.Therefore,a series of microarray electrodes with micro-nano structures were designed based on photolithography technology in this paper.Conductivity of the electrode was imparted by subsequent gold spraying?two-step method?or mixing with a conductive filler?one-step method?.A sensing model with high electrochemical activity was successfully constructed based on the three-dimensional electrode which greatly increased the specific surface area and roughness of the electrode.The specific contents are as follows:1.Preparation and application of high aspect ratio three-dimensional microarray electrode by photolithography technologyA series of three-dimensional microarray structures with different diameters and different aspect ratios were designed and fabricated with the photoresist SU-8 2000.The micromorphology was characterized to demonstrate the successful preparation of the three-dimensional microarray structure.The conductive nano-gold layer was introduced by vacuum sputtering because the polymer layer is electrically insulating.Then,the electrochemical performance of gold/microarray was characterized,which showed that the gold/microarray electrode with three-dimensional structure has an ultra-high electrochemical response current.The response current of the 3D electrode with three times specific surface area of the planar electrode can be increased to 13 times of the planar electrode,which demonstrated the inherent advantages of three-dimensional electrode.Finally,in order to verify the practical applicability of the electrode,a simple hydrogen peroxide non-enzymatic sensor was constructed by in situ electrochemical reduction of copper nanoparticles.The sensor exhibited an ultra-high sensitivity to hydrogen peroxide(310.6?A mM^-1 cm^-2,R²=0.999)and had good sensing properties.2.Preparation and sensing application of graphene/SU-8 composite photoresistThe conductivity is an important property of the electrode.In the previous chapter,it required secondary gold spray because the SU-8 2000 photoresist is electrically insulating,which increased the process steps and equipment requirements.The rise of composite materials solved this problem,which provided a new idea for the one-step direct preparation of conductive micro-nano structures.Therefore,in this chapter,a composite photoresist with conductivity was prepared by incorporating a conductive filler?graphene?into the photoresist.The effect of graphene contents on the conductivity and dispersibility of the system was studied.The result showed that the composite photoresist with a higher graphene contents has better conductivity and poorer dispersion.Simultaneously,the composite photoresist?4wt%GR?with the balanced performance not only had the conductivity but also had the patterning function of the photoresist.Subsequently,a non-enzymatic sensor was constructed using the obtained electrode with a conductive micro/nano structure as a transducing element?method as above?.The sensor exhibited good sensing performance and demonstrated the feasibility of the one-step method for preparing conductive patterns/electrode.3.Preparation and sensing application of AgNW/GR/SU-8 composite photoresistIt is inefficient of forming a conductive network when the system contains only the lamellar conductive filler.Some researches showed that the introduction of a small amount of one-dimensional filler can promote the formation of a conductive network because the one-dimensional filler can act as a“bridge”between the two-dimensional fillers.This method can prepare the composite system with better conductivity,which is advantageous for preparing an electrode with higher electrochemical activity.Therefore,this chapter used silver nanowires?AgNW?and graphene?GR?as common fillers to prepare a composite photoresist system.The effect of the contents of conductive filler on the conductivity and dispersibility of the system was studied.It was found that when the graphene was 3wt%and the silver nanowire was 0.75wt%,the conductivity and dispersibility of the composite system reached equilibrium.Moreover,the conductivity of AgNW/GR/SU-8 composite photoresist was greatly improved compared with the GR/SU-8system,which proved the"bridge"effect of the linear material in the two-dimensional structure.Subsequently,a non-enzymatic sensor was constructed using an electrode with a conductive micro/nano structure as a transducing element?method as above?.The sensor exhibited better sensing performance than the GR/SU-8 system and demonstrated the feasibility of the one-step method for preparing conductive patterns/electrode.