Microfiber Optic Dopamine Sensor Based On Au-Cu_2-xS Resonant Coupling Enhancement

Dopamine controls stress response,consciousness,learning,sleep-wake cycle,motivation,and memory formation in the body.Its low levels of dopamine contribute to the development of various neurodegenerative diseases and its spontaneous oxidation causes a significant oxidative load on neurons.However,most of the existing detection methods require expensive equipment,complex pre-processing procedures,and is of poor sensitivity and stability.The fiber optic biosensor can sense the precise concentration change of its surface through the high-resolution refractive index sensing method.It can detect the dynamic process of dopamine biomolecules in vivo and virto with the advantages of strong anti-electromagnetic interference ability,label-free and high mechanical flexibility.Since dopamine is a small molecule.Recently,most of the fiber-optic dopamine sensors in the laboratory have focused on improving the detection limit.They have not investigated the oxidation and release process in neuronal cells.Facing the above,we develop a fiber-optic sensor with ultrahigh sensitivity for dopamine detection and investigate its oxidation and release process.The research contents and results are as follows:1.The coupling of Au@MoS₂ and Cu_2-xS@GO was designed to increase the energy density of evanescent field on the fiber surface.Gold nanoparticles enhances the evanescent field of microfiber with the plasmonic electromagnetic enhancement.MoS₂ increases the charge transfer of Au@MoS₂ and further improves this effect.The localized surface plasmon resonance frequency of Cu_2-xS was tuned to the near infrared range to match the frequency of microfiber evanescent wave.And graphene oxide（GO）with good biocompatibility was selected to wrap Cu_2-xS to achieve covalent binding to single-stranded DNA.The aptamer,as a bridge connecting the Au@MoS₂ layer and the Cu_2-xS@GO nanoparticle,shortened the distance between these two and caused electromagnetic field coupling through conformational transition after capturing the dopamine molecule.Thus,the dopamine bond at the electromagnetic field coupling-enhanced site between the Au@MoS₂ layer and the Cu_2-xS@GO nanoparticle.2.The sensitization mechanism of aptamer phase transition was introduced.The Au@MoS₂and Cu_2-xS@GO are sequentially modified to the fiber surface,which are connected by single-stranded DNA（ss DNA）.The small refractive index change caused by the dopamine binding is translated into a large refractive index change induced by the conformational transition of an aptamer with a Cu_2-xS@GO nanoparticle attached to its end.With the dual-amplified enhancement of the nanointerface,the microfiber exhibited an ultrahigh sensitivity for detecting dopamine molecules at the single-molecule level and presented a limit of detection of 7.83 a M in pure solution and 55 a M in artificial sweat.3.Free iron ions in the human body are the main cause of dopamine oxidation.The optical microfiber sensor in this work is employed to monitor the oxidation process of dopamine molecules.In addition,it also can be explored to trace the dopamine release from dopamine neuroergic cells under electrical stimulation.