Preparation and Application of Single Nanoelectrode

Author:Wang Dong Mei

Supervisor:li yong xin


Degree Year:2018





Nanoelectrodes are widely used in the field of electrochemical research due to their advantages of small charging current,fast transfer rate and smaller solution resistence,such as the study of electron transfer kinetics,high resolution imaging for scanning electrochemical microscopy(SECM),and detection of individual molecules and single nanoparticle.It is well known that precious metals(such as gold,platinum and silver)have excellent electrocatalytic activity,reactivity and surface-enhanced Raman(SERS)activity.However,there are relatively few studies on the application of single metal nanoelectrode.Based on this,the paper aims to prepare single nanodisk electrode and nanowire electrode though laser-assisted pulling technique and etching process and study its application in the construction of biological sensor and electrocatalysis.The main work is as follow:1)Single Au nanowire electrodes(AuNWEs)were fabricated by laser-assisted pulling/Hydrofluoric acid(HF)etching process,which then were characterized by transmission electron microscopy(TEM),electrochemical method and finite-element simulation.The as-prepared single AuNWEs were used to construct electrochemical aptamer-based nanosensors(E-AB nanosensors)based on the formation of Au-S bond that duplex DNA tagged with methylene blue(MB)was modified on the surface of electrode.In the presence of adenosine triphosphate(ATP),the MB-labeled aptamer dissociated from the duplex DNA due to the strong specific affinity between aptamer and target,which lead to the reduction of MB signals.Moreover,BSA was employed to further passivate electrode surface bonding sites for the stable of the sensor.The as-prepared E-AB nanosensor has been used for ATP assay with excellent sensitivity and selectivity,even in a complex system like cerebrospinal fluid of rat brain.Considering the unique properties of good stability,larger surface area and smaller overall dimensions,this E-AB nanosensor should be an ideal platform for widely sensing applications in living bio-system.2)A label-free electrochemical apta-nanosensor fabricated on single gold nanodisk electrode(AuNDE)for thrombin sensing with high sensitivity was developed via a novel signal amplification strategy.This recognition platform was fabricated via self-assembly of helper DNA(HP-DNA),thrombin aptamer(TBA)and gold nanoparticles(AuNPs)-DNA complexes to form a sandwich structure on AuNDE surface.A novel signal amplification strategy via designed AuNPs-DNA complexes was introduced using Ru(NH3)63+as the signal reporter based on the electrostatic interaction.In the presence of thrombin,the strong interaction between aptamer and target led to the dissociation of sandwich DNA complexes from AuNDE,which resulted in the reduction current of Ru(NH3)63+.This proposed sensing platform showed a wide detection range of 0.1 pM~5 nM and a low detection limit of 0.02 pM.Considering the small overall dimensions and high sensitivity,this nanosensor can be potentially applied for bioanalysis in living biosystem.3)Utilizing the effect of proximity-dependent hybridization,a bipedal DNA walker based on DNA hybridization was designed for the detection of miRNA-21.First,the hairpin helper DNA was fixed on the electrodes as the orbital,and the bipedal DNA walker was built through the hybridization of two hairpin DNA modified with the azide(N3)and dibenzo(DBCO),respectively.The hybridization occurred and the penta cyclic compound was synthesized simultaneously.Then,the two-legged DNA walker was constructed.When the target miRNA was added,it opened the hairpin structure of DNA walker and hybridized with orbital hairpin DNA via proximity effect to expose the prelocked toehold domain of orbital DNA for the hybridization of MB-labeled fuel DNA.The toehold-mediated strand displacement reaction brought the electro-chemical signal molecule MB close to the electrode and meanwhile released the bipedal molecular machine to traverse the sensing surface by the surface programmatic chain reaction.Using miRNA-21 as a model target,combine with the advantages of single nanoelectrode and sensor based on bipedal molecular machines,this method showed a linear detection range from 0.5 fM to 50 pM with a detection limit of 60 aM.The proposed detection strategy was enzyme-free and allowed highly sensitive and selective detection of a variety of DNA or RNA by using corresponding DNA-based affinity probes,showing potential application in bioanalysis.4)Single Ag nanowire electrodes and single Ag@Pt nanowire electrodes were simply fabricated by laser-assisted pulling technique and etching process.There is still a challenge to pull a single silver nanoelectrode.We successfully prepared a single Ag nanodisk electrode by adjusting the parameters and steps of the gold nanoelectrode and obtained nanowire by etching it in HF solution.The Ag nanowire electrode is characterized with transmission electron microscopy,EDS and electrochemistry.In order to better explore the application of Ag nanowire,we prepared single Pt@Ag nanowire electrode through metal displacement reaction and characterized it with high-resolution transmission electron microscopy,EDS and electrochemistry.We also investigated its catalytic performance in MOR,and also monitored its catalytic performance in 4-nitrophenylthiophenol reduction reaction with SERS.The experimental results showed that the catalytic performance of Pt@Ag nanowire for methanol in alkaline solution was significantly higher than that of commercial Pt/C catalyst,and the Pt@Ag nanowire had good catalytic performance for the reduction of 4-nitrophenylthiophenol in the presence of NaBH4.