Electrochemical Detection Of Biomolecules Based On Novel Stimuli-responsive Polymers

It has been reported that the pathogenesis of Alzheimer's disease(AD)is closely related with a variety of biomolecules.However,the concentration of endogenous biomolecules in brain is low and the biological environment is complex.Besides,it is difficult to accurately diagnose disease with a single biomolecule.Therefore,the sensitive and selective detection of various AD-related molecules is an important means of elucidating the mechanism of neurodegenerative diseases at the molecular level,which is important for the diagnosis of disease.Based on the "recognition-mediating-function"(RMF)design concept,we designed and synthesized a variety of novel stimuli-responsive polymers.Based on the hydrogen bonds,these polymers can translate the recognition of biomolecules into their macroscopic properties.In addition,compared with small-molecule organic probes,the recognition efficiency of these polymer is higher due to multiple hydrogen bonds.Due to the function integration of the polymer,we can synthesize multi-responsive polymers.Considering the excellent characteristics of electrochemical methods,we modified stimuli-responsive polymers onto the surface of screen-printed electrodes.The conformation and wettability changes were beneficial for the access and enrichment of redox labels and biomolecules to the electrode surface,thus,largely improving the sensitivity of electrochemical assays.Besides,the charge transfer resistance(Rct)decreased after the addition of target sugar,easily avoiding the fake signal by potential interferences.Compared with traditional electrochemical sensors,nanopore possess confined space.The subtle changes of the physical /chemical properties in the confined space may largely amplify the identification signal to realize the ultrasensitive detection of molecules.In addition,due to its advantages of easily made,low cost,excellent mechanical and chemical stability,and adjustable orifice diameter,the glass nanopipette-based nanopore platform is attracting more and more attention.In this paper,we developed novel glass nanopipette based on stimuli-responsive polymers.The changes of the polymer morphology or the charge in inner wall may affect the ion current in the napore.In order to study the role that different biomolecules play in the pathogenesis of AD,we designed a dual stimuli-responsive polymer and detected two biomolecules on the same platform.Moreover,by utilizing microdialysis,we can detect biomolecules in different brain regions of AD mice.The full text is divided into five parts,as follows:Chapter 1: Overview This chapter mainly introduces the research background and detection method of AD-related biomolecules,the properties,the classification,the synthetic methods and applications of stimuli-responsive polymers.We focus on the preparation and properties of stimuli-responsive polymers based on the “RMF” design concept and the application of stimuli-responsive polymers in electrochemical biosensors.Finally,we proposed the concept of this paper.Chapter 2: Signal amplification detection of monosaccharides enantiomers based on stimuli-responsive copolymer/graphene hybrid-modified electrode interface In this work,a novel stimuli-responsive copolymer/graphene composite was synthesized through atom transfer radical polymerization(ATRP).Based on the signal amplification of this material,we established an electrochemical method with high sensitivity and selectivity for monosacharrides.On the one hand,through the synergetic hydrogen-bonding interactions,the polymers could translate the recognition of monosaccharides into their conformational change,which increased the active area of the electrode and the accessibility of redox substrates onto electrode surfaces.On the other hand,the conformational change of copolymer chains induced advantageous wettability responses,which facilitated the enrichment of monosaccharides and redox labels near the electrode surface,thus,largely improving the sensitivity of electrochemical assays.The detection limit of glucose in this work is as low as 1 n M.In addition,this method showed not only chiral distinguish ability toward different monosaccharide enantiomers,but also good selectivity toward monosaccharides in comparison to potential interference molecules.Finally,the electrodes were successfully applied for discriminating glucose enantiomers in live cells and studying their different transport mechanism.Based on the significant analytical performance and “RMF” design principle,the present work provided a new methodology to design sensitive and selective electrochemical sensors for other biomolecular species related with AD.Chapter 3: Rational design of a stimuli-responsive polymer electrode interface coupled with in vivo microdialysis for measurement of sialic acid in live mouse brain in Alzheimer's disease Sensitive and selective monitoring of sialic acid(SA)in cerebral nervous system is of great importance for studying the role that SA plays in the pathological process of AD.In this work,we first reported an electrochemical biosensor based on a novel stimuli-responsive copolymer for selective and sensitive detection of SA in mouse brain.Notably,through synergetic hydrogen-bonding interactions,the copolymer could translate the recognition of SA into their conformational transition and wettability switch,which facilitated the access and enrichment of redox labels and targets to the electrode surface,thus significantly improving the detection sensitivity with the detection limit down to 0.4 p M.Besides amplified sensing signals,the proposed method exhibited good selectivity toward SA in comparison to potential interference molecules coexisting in the complex brain system due to the combination of high affinity between phenylboronic acid(PBA)and SA and the directional hydrogen-bonding interactions in the copolymer.The electrochemical biosensor with remarkable analytical performance was successfully applied to evaluate the dynamic change of SA level in live mouse brain with AD combined with in vivo midrodialysis.The accurate concentration of SA in different brain regions of live mouse with AD has been reported for the first time,which is beneficial for progressing our understanding of the role that SA plays in physiological and pathological events in the brainChapter 4: Ultrasensitive detection of ?-amyloid(A?1–40/1–42)based on glass conical nanopores modified with stimuli-responsive copolymer In the pathological progress of AD,the aggregation of ?-amyloid(A?)is susceptible to the chemical composition on the cell membrane.Sialic acids(SAs),located on the terminal position of brain gangliosides,work as bridges for the binding between ganglioside and A?,promoting a conformational transition of A?.In this work,we designed and synthesized a new three-component copolymer containing sialic acid as the recognition unit.The copolymers were introduced onto the glass conical nanopores through covalent bonds,achieving a simple,low-cost and ultrasensitive platform for detecting A?(1–40/1–42).Upon treated with A?,the conformation of copolymer could translate from contraction state into stretched state,which led to the reduction of effective pore size.Then,the ion current through the nanopore decreased.Based on the signal amplification of glass conical nanopore with a confined space,A?(1–40/1–42)monomers could be detected with a detection limit down to 3.2 f M.Besides,this method exhibited good selectivity.By combining with in vivo microdialysis,this copolymer-modified glass nanopore with remarkable analytical performance was successfully applied to evaluate the concentration of A?(1–40/1–42)monomer in live mouse brain with AD.This work has not only established an effective method for detecting the concentration of A? monomer in the pathological process of AD,but also provided a new methodology to design novel glass nanopores based on stimuli-responsive polymers for the detection of multiple biomolecules related with AD.Chapter 5: Detection of zinc ion and ?-amyloid(A?1–40/1–42)based on glass-conical nanopores modified with double-responsive copolymer In this work,we synthesized a novel stimuli-responsive polymer containing sialic acid(SA)and quinoline derivatives(AQZ)as recognition functional units.Then,the copolymer was introduced onto the glass conical nanopores through covalent bonds,achieving a platform for detecting both A? monomers and Zn2+.In this method,the AQZ units could combine with Zn2+ through metal coordination.Thus,the inner surface charge changed and the ion current at the negative voltage decreased.Upon treated with A?,the polymer chain in the pore relaxed.Then,the effective diameter of the nanopore reduced,eventually the ion current in the pores decreased.In addition,the fluorescence intensity of the glass inner wall changed after being treated with target molecules due to the fluorescence characteristics of AQZ.In summary,this system can not only detect two biomolecules on the same platform,but also provide a new methodology to design novel glass nanopores with dual signal response.