Application Of Local Surface Plasmon Resonance Of Gold Nanoparticles In Nucleic Acid Assay

Noble metal nanoparticles especially gold nanostructures possess unique optical and electrical properties which have earned extensive attention.Localized surface plasmon resonance(LSPR)is one of the defining properties which displays the collective oscillations of free electrons in metal nanoparticles driven by the electromagnetic field of incident light.The LSPR wavelength shift in extinction spectra and electromagnetic field enhancement around the particles were greatly dependent on the materials,size,shape,surrounding medium,and aggregation states of individual nanoparticles.The ECL behaviors of semiconductor nanocrystals(NCs)were sensitive to the LSPR effect induced by gold nanoparticles(GNPs)with different shape and coupling status,which provide a novel strategy and broaden the application of GNPs for biosensors and life assay.Based on the LSPR of GNPs,the plasmon coupling induced ECL responses and scattering signal changes were investigated.We constructed ultra-sensitive biosensors for the detection of nucleic acid both in vitro and in living cells.The details are summarized as follows:1.Mechanism and application of plasmon coupling induced ECL enhancementWhen two nanoparticles are brought into close proximity,the individual plasmons couple to dimers,leading to the shift of LSPR in extinction spectrum and significant enhancement of EM fields especially in the interparticle junction between two plasmons.We construct the gold nanoparticle dimers on the surface of electrode,and take insight into the ECL enhancement induced by the "hot spot" in the interparticle junction between two plasmons.We constructed 5 nm AuNP monomers and dimers on top of CdS NCs modified GCE,and observed greater enhancement of ECL intensity by AuNPs dimer than that by monomer.To explain the phenomenon,FDTD method,an algorithm to solve Maxwell's curl equation on a discretized spatial grid,was applied for theoretical study.The simulation confirmed enhanced EM field caused by the plasmon coupling.The largest |E|2 values of 5 nm Au dimer shows 2.4 fold to that of monomer,which serves as the key reason for the improved ECL enhancement.We demonstrated the mechanism of the LSPR-ECL enhancement using Jablonski diagram to explain the distance effect,and used the fluorescence lifetimes of CdS,CdS/Au monomer and CdS/Au dimer to simulate the ECL decay times,which agreed well with ECL emissions.The plasmonic coupling strategy shows perspective in ultra-sensitive bioassays.We employ a target induced recycling amplification assisted with DSN enzyme for the detection of microRNA-21(miRNA-21)based on the GNP dimers induced ECL signal enhancement.The CdS nanocrystals(NCs)dropped on the surface of glassy carbon electrode(GCE)were functioned as ECL emitters.In the presence of target miRNA-21,the hairpin-like probe DNA(pDNA)was opened and hybridized with miRNA to form rod-like duplex.Followed by the recognition and cleavage with DSN enzyme,the miRNA-21 was released and subsequently hybridized to another pNDA strand for circles.Finally,pDNA strands with short domain remained on the surface provided locations for GNP dimers,causing a significant enhancement of ECL intensity.We demonstrated the influence of diameters of GNPs theoretically and experimentally,and optimized the distance between GNP dimers and CdS NCs.Under optimal conditions,the concentration of miRNA-21 was sensitively determined in a wide linear range from 10 fM to 20 pM,which showed great potential in the construction of LSPR-ECL biosensors,and broaden the application of noble metal nanoparticles in biosensors.2.Plasmon-enhanced electrochemiluminescence for nucleic acid detection based on gold nanodendritesGold nanodendrites(Au NDs)exhibit extremely strong electromagnetic field located around multiple tip branches due to a plasmon coupling effect.We report a novel plasmon coupling-induced enhancement of ECL from CdTe nanocrystals(NCs)film by Au NDs for the detection of nucleic acid,in which the CdTe NCs film modified on glassy carbon electrode(GCE)as an ECL emitter and Au NDs as both quencher and enhancer.The DNA tetrahedral embedded with a stem-loop hairpin structure on one edge was applied as a switch to regulate the distance between CdTe NCs and Au NDs.In the present of target DNA,the hairpin structure stretched from a"closed" stage to rod-like by hybridizing to both the stem and the loop,and the DNA tetrahedral reconfiguration switched from relaxed stage to taut stage and reached to a large distance.Since LSPR enhanced ECL is distance mediated,the configuration change of DNA tetrahedral resulted in an obvious enhancement of ECL signal.The concentration of target DNA was sensitively determined via such strategy.Combined with controllable asymmetric functionalization of Au NDs,the ECL signal of constructed DNA tetrahedral nanoswitch performed great stability and reproducibility in the range of 1.0 to 500 fM,with the detection limit of 30 aM.Considering the high sensitivity and selectivity in the serum sample assay,we believe that this study could broaden the perspective of non-spherical noble metal nanoparticles for further development of LSPR enhanced ECL biosensors.3.Exploration of the kinetics of toehold-mediated strand displacement via plasmon rulers in living cell analysisDNA/RNA strand displacement is one of the most fundamental reactions in DNA and RNA circuits and nanomachines.We report an exploration of the kinetics of the toehold mediated strand displacement process via core-satellite plasmon rulers.Other than conventional fluorescence kinetics experiment,no additional fluorescent reporting reaction was needed in this system,and the dynamic process could be observed in living cells.The kinetic calculating mode is based on the cumulative probability of strand displacement events,which caused satellite leaving from the core.Via continuously monitoring the scattering signal of plasmon rulers,kinetic parameters of the toehold-mediated strand displacement triggered by a short sequence of miRNA-21 were calculated.We noted that in different matrixes,there was a big difference of deduced second-order rate constants,indicating the impact of surrounding medium to the displacement kinetics.In addition,the influence of invader strand type and toehold length were investigated.Applying several coresatellite plasmon rulers as nanoprobes,kinetic study in living cells was proceeded.The reaction rate constant and expression of microRNA-21 in living cells have been deduced and compared with the acquired data in vitro.The advantages of unique plasmon rulers enable the monitoring and modulating of dynamical biological processes,and monitoring gene expression in living cells.Assisted with statistic analysis,the quantitative detection of microRNA-21 in HeLa cells has been conducted successfully.