Construction Of Novel Optical Sensor Based On Noble Metal Nanomaterials And Application In Biomarker Detection

Noble metal nanomaterials possess great surface area and apparent surface plasmons resonance effect and dielectric confinement effect,they display excellent physical,chemical,optical performance,including good stability?no bleaching phenomenon?,high yield,high conductive capability,catalytic performance and good biocompatibility.Base on these feactures,noble metal nanomaterials are widely used in electrochemical and biological sensors and photothermal therapy field,etc.In this paper,we focused on these features of nanomaterials including surface plasmon resonance effect,plasmon coupling effect,fluorescence and the characteristics of great surface area,and illustrated these applications in detecting biological markers having important clinical significance such as Uracil-DNA glycosylase?UDG?,miRNA,Alzheimer's protein.We constructed new optical biosensors as following:Firstly,a chemiluminescence sensor for uracil glycosylase?UDG?detection with high efficiency,high sensitivity and high signal-to-noise ratio has been developed to catalyze luminol chemiluminescence reaction,which was based on the three-way junction?TWJ?structure-driven strand displacement reaction and the formation of G-quadruplex spherical nucleic acid enzyme?G4-SNAzyme?actuated by DNA walker technology.The system was composed of TWJ structure and spherical nucleic acid structure?SNA?.The TWJ structure included three kinds of chains:DNA hairpin with closed walker,probe with U base,and substrate chain to maintain the stability of the system.Spherical nucleic acid structure?SNA?was a nucleocapsid structure formed by the DNA coated on the surface of AuNPs.There were two kinds of strands modified on the surface of AuNPs,one was used to hybridize with TWJ structure,and the other was used for forming G-quadruplex DNAzyme.Target uracil glycosylation enzyme removed U bases in UP probe with high specificity and left an apurinic/apyrimidinic?AP site?.With the aid of Endo IV,the UP probe was cut off and toehold region was exposed.At this point,the strand in the SNA will hybridize with the TWJ structure,triggering the chain replacement reaction mediated by toehold and the subsequent DNA walker reaction.Eventually,the blocked G-quadruplex DNA on surface of AuNPs was released.In the presence of hemin and K⁺,many G-quadruplex DNAzyme structures were formed on the surface of gold nanoparticles,forming G4-SNAzyme with strong peroxidase activity.G4-SNAzyme could catalyze luminol to generate chemiluminescence signals in the presence of H₂O₂.Different from the traditional G-quadruplex DNA enzyme catalyzing the luminol chemiluminescence reaction,G-quadruplex DNA enzyme was modified on the surface of gold nanoparticles owning large specific surface area,which acted as a kind of enrichment effect,thereby significantly improved the peroxidase activity of G4-SNAzyme,chemiluminescence signal was significantly enhanced.This method was characterized by high signal-to-background ratio,high sensitivity and good selectivity.It provided a simple and effective platform for detecting the concentration of uracil glycosylase in tumor cells.Secondly,a sensitive and simple fluorescent biosensor for miRNA detection has been developed based on DNA three-way junction?TWJ?-driven strand displacement reaction and fluorescence light-up AgNCs probe.The analysis units of this method were composed of the closed G-rich DNA hairpin,the complementary strand of target,the substrate chain that maintains the stability of the system,and the AgNC probe that generated fluorescence signal.MiRNA hybridized with complementary strand and the TWJ structure would be changed,which triggered the toehold in G-rich DNA hairpin exposed.The fluorescence of the silver cluster was significantly enhanced.AgNC probe hybridized with the toehold region,triggering the occurrence of toehold-mediated strand displacement reaction.Eventually AgNC-SP/GrHP structure was formed and the fluorescence of AgNCs was enhanced.By means of strand displacement reaction,the system achieves rapid chain migration process without the aid of enzyme,which not only reduced the cost but also effectively reduced the effect of enzyme on fluorescence of AgNCs.This method had advantages of simple operation,high signal-to-noise ratio and strong fluorescence response,providing a reliable platform for the detection of miRNA.Thirdly,we constructed a robust and convenient surface-enhanced Raman scattering?SERS?biosensing platform for simultaneous detection of A??1-42?oligomers and Tau protein using different Raman dyes-coded polyA aptamer-AuNPs?PAapt-AuNPs?conjugates.In this method,two kinds of AuNPs labeled with different Raman dyes?DTNB and 4-AATP?were designed,and polyA-aptamers were respectively modified on the surface of the two kinds of AuNPs.The aptamers were used to capture the target and the polyA oligonucleotide sequences were used to anchor the surface of AuNPs.After the specific binding of the target Tau protein/A??1-42?oligomers and their aptamers respectively,polyA oligonucleotides could deviate from the AuNPs surfaces,which destroyed the stability of nanoconjugates in the solution,resulting in the plasmonic coupling effect between adjacent AuNPs,and enhancing the SERS signal of dyes between AuNPs.This was the first time that polyA coated AuNPs were used for protein markers detection.This method had high sensitivity and specificity and provided a simple and reliable method for the early clinical diagnosis of Alzheimer's disease.