Study Of Electrochemical Aptasensor Based On Silver Nanoparticles

Due to the superiority in sensitivity,simplicity,cost and miniaturization,electrochemical biosensor is one of the mostly used analytical methods for life science.The development of ultrasensitive electrochemical biosensor for detecting disease-related proteins is of particular importance in clinlic dignostic and reseach field.Aptamers have been used as biological recognition elements in the application of electrochemical biosensors,because of their characteristic of cost-effective synthesis,high binding affinity and flexibility for signal transduction.Screen printed electrode,taking advantage of low cost,high sensitiveity,good reproducibility and mass production ability,can meet the requirements for rapide and in situ analysis.The combination beteween nanomaterials based signal amplification and electrochemical biosensing technique have drawn more attentions in the current researches.Metal nanoparticles have shown distinct physical and chemical properties,among which,silver nanoparticles(AgNPs)have attracted increasing attention for applications in chemistry and biomedical science,according to their unique optical,electrical,chemical and catalytic properties.In this thesis,the biofunctionalization and electrochemical detection of AgNPs was studied on the assay platform by using screen printed electrodes.Several electrochemical biosensors based on AgNPs as well as aptamers were developed for the analysis of biomarkers.The main content includes the following aspects:1.Study on the development of aptasensor based on micro screen printed electrode and multiwell plate.In this chapter,an assay platform based on micro screen printed electrode as well as multiwell plate was designed for the development of electrochemical aptasensor for platelet derived growth factor BB(PDGF-BB)detection using catalytic silver enhancement induced by AgNPs.Biotinlayted aptamer was immbolized on the streptavidin-coated microplates,and AgNPs modified with thiol functionalized aptamer was used as detecting probe.Through a sandwich-type reaction,massive deposition of silver promoted by AgNPs was formed in the sensor system.The deposited silver was dissolved in acidic solution,releasing numerous silver ions,which was easily detected by square wave anodic stripping voltammetry.The stripping peak current of silver was related to the concentration of PDGF-BB.Under the optimal conditions,the sensor showed a good analytical performance towards PDGF-BB,displaying a wide dynamic range from 3.12 ng mL"1 to 200 ng mL"1 with a detection limit of 1.23 ng mL-1.This sensing strategy would have a promising future for detection of biomarkers with high specificity and sensitivity in clinic diagnostic.2.Fabrication of streptavidin functionalized silver nanoparticles decorated graphene and its application in electrochemical aptasensor.In this chapter,silver nanoparticles and graphene hybrid(AgNPs/graphene)was fabricated according to a self-assembly procedure followed by functionalization with streptavidin(SA).SA functionalized AgNPs/graphene(SA-AgNPs/graphene)was used as electrochemical label in the electrochemical detection of human immunoglobulin E(IgE)through a sandwich-type strategy.The thiol-capped IgE DNA aptamer was immbolized on the gold nanoparticles modified screen printed electrode,and was used as capture probe for IgE.SA-AgNPs/graphene linked with biotinylated goat anti-human IgE antibody was used as detection probe.During the assay process of the sensor,the electrochemical stripping response from AgNPs anchored on the graphene was used as signal output for quantitavely detecting IgE.The results demonstrated that this electroehemical aptasensor possessed a dynamic range from 10 to 1000 ng mL-1 for IgE,with a low detection limit of 3.6 ng mL-1.The proposed electrochemical aptasensor in this work also provides a sensitive and fast electrochemical sensing platform for other protein detection.3.The development of signal amplification based on silver nanoparticles aggregate and its application in electroehemical aptasensor.In this chapter,a signal amplfication strategy was designed for the development of electrochemical aptasensor based on the combination of the hybridization inducing aggregation of AgNPs and detection for silver by differential pulse andonic stripping voltammetry.The capture aptamer that specifically recognizes PDGF-BB was immobilized on gold nanoparticles modified screen printed electrode array.After a sandwich type reaction,two kinds of DNA-modified AgNPs were simultaneously added on the electrode surface for specifically recognizing PDGF-BB and forming the AgNPs aggregate caused by in situ hybridization of DNA.Compared to the single labeled tag,the tracing aggregate tags showed a strong electro-activity for signal..amplification through stripping detection of silver after pre-oxidization.The sensor showed a wide linear range and a lower detection limit by using the proposed strategy.The multiplied protein assay for PDGF-BB and Thrombin on the SPE array chip was achieved.The cross-talk between different aptamer modified electrodes on the same array was avoided because of the advantage of DNA modified AgNPs with reasonable design.The array detection was also applied in the logic gate operation.The proposed method described here is ideal for multi-analytes determination in clinical diagnostics with good analytical performance.4.Signal amplification strategy in the electrochemical aptasensor based on the synergy effects of silver nanoparticles catalysis and electropolymerizationIn this chapter,a novel electrochemical aptasensor based on magnetic separation platform was designed for highly sensitive determination of PDGF-BB.Owing to the amplified catalysis of AgNPs aggregates induced by DNA in situ hybridization,the o-nitrophenol(o-NP)was reduced to o-aminophenol(o-AP)by NaBH4.The produced o-AP was electro-co-deposition with multiwalled carbon nanotubes(MWCNTs)on the screen printed electrode,producing a conducting nano-composite.The signal readout in this aptasensor for PDGF-BB was obtained by direct measurement of the poly(o-AP-MWCNTs)film on the screen printed electrode.Under the optimal conditions,the assay displayed a wide dynamic working range of between 0.1 ng mL-1 and 100 ng mL-1 with a detection limit of 60 pg mL-1 relative to target PDGF-BB.Incorporation of good catalytic ability of hybridization inducing AgNPs aggregates and excellent electrochemical property of poly(o-AP-MWCNTs)nanocomposite,the electrochemical signal was amplified.Owing to the high loading of catalytic AgNPs as well as the electro-catalytic ability of MWCNTs through electrodepositon,this method would have a promising future for application in clinical diagnostics.