LSPR Response Of Gold Nanoparticle Assemblies For Dark-field Imaging Of MicroRNA In Tumor Cells

Due to their unique localized surface plasmon resonance（LSPR）effect,noble metal nanoparticles are widely used in the research of sensing,catalysis and imaging at the single particle level.Based on this,researchers have developed a large number of plasmonic sensing platforms for biological and chemical analysis.The incident light causes the collective oscillation of electrons on the surface of plasmonic nanoparticles,and its scattering cross section is limited to about 10^-10 cm^-2,but the luminosity is about 500,000 times that of fluorophores of the same size,making LSPR sensors have higher sensitivity.The LSPR effect of nanoparticles can be adjusted in many ways:on the one hand,the scattering spectrum of a single particle can be changed by changing the composition,shape and size of nanoparticles.According to this characteristic,plasmas of various shapes and sizes Nanoparticles are widely used,such as spherical,rod-shaped,urchin-shaped,etc.;on the other hand,it can also be tuned by coupling/decoupling,so changing the plasmonic coupling between two or more nanoparticles can be done with for measuring distances between nanoparticles or monitoring reactions.In recent years,using dark field microscopy（DFM）imaging technology,single particle dark field detection has been widely used in the detection and imaging of various molecules,nucleic acids,proteins,cells and other tumor markers.Compared with other detection methods,dark-field microscopy imaging technology shows unique detection advantages,such as low background signal,high temporal and spatial resolution,small and controllable size,etc.In dark-field scattering imaging,noble metal nanoparticles,especially gold nanoparticles,are often used as scattering probes.However,the common response signal based on the LSPR effect of gold nanoparticles is single,and the concentration change of the target can be determined only by the shift of the probe scattering peak or the change of particle color.When the content of the target is low,a signal amplification strategy is needed to ensure the signal strength of the detection.In addition,usually only one target is selected to trigger a single signal response in detection,and the process of double target identification or double signal response is less,and false positive detection results are prone to occur.Therefore,the construction of a dual target response or a single target multiple signal response system is conducive to improving the accuracy of detection results.In this paper,two microRNA sensing strategies are designed,using one target to induce a dark-field-fluorescence dual signal response,or using a dark-field plasmonic nanoprobe to simultaneously detect two targets,in order to improve tumor markers.The accuracy of the detection concentration and the reliability of the early diagnosis of the disease provide new ideas.1.Development of novel nucleoid-satellite structured plasmonic nanoprobes for ultrasensitive detection of tumor markers in dark-field-fluorescence dual mode.The plasmonic nanoprobe uses gold nanoparticles（Au NPs）as the core and silver nanoclusters（AgNCs）as the satellites,and the constructed Au NPs-AgNCs plasmonic nanoprobe has a stable LSPR scattering signal.In the presence of the target microRNA-21,a continuous strand displacement reaction on the probe surface was induced to release the silver nanoclusters on the probe,causing a change in the coupling state of the plasmonic probe to display a dark-field scattering signal response.The color and intensity changes of particle imaging observed under dark-field microscopy can be distinguished by naked eyes,and are highly correlated with the concentration of miRNA-21 from1f M to 1n M.At the same time,the release of silver nanoclusters caused the recovery of its fluorescence,and the hybridization with the complementary strand rich in G bases caused a significant increase in fluorescence,thereby realizing the dark field-fluorescence dual-mode detection.Further,the imaging results of miRNA-21 in HeLa cells were analyzed,showing accurate detection and anti-interference ability in complex samples.2.A DNA-Au tetramer-based pyramid-shaped plasmonic probe was designed for the logic-response detection of two microRNAs.The probe consists of four 30nm Au NPs connected through the central DNA tetrahedron to form a tetramer structure.Due to the plasmonic coupling effect,the gold tetramer has a strong scattering signal.When one of the targets,microRNA-141,exists,a strand of the DNA tetrahedron dissociates and takes away a particle in the pyramid structure,resulting in a certain change in the plasma coupling state,corresponding to a dark field signal response;and When another target,microRNA-21,exists at the same time,the DNA tetrahedron structure dissociates completely,causing the pyramid structure of the Au NPs tetramer to disintegrate into individual scattered gold particles,and the plasma coupling state changes greatly,which can be directly observed Visible changes in dark field signal.The change of the gold particle coupling state is caused by the change of the DNA tetrahedral structure,and the detection of the dual target is realized.Due to the designable and easy-to-program characteristics of DNA sequences,two microRNAs that are highly expressed at the same time in a certain disease can also be selected,and the base sequence of the recognition region in the DNA tetrahedron can be correspondingly modified to realize dual-marker detection for diseases,thereby improving Accuracy of early warning or diagnosis of disease.