Plasmonic Nanopore-based Study On β-Amyloid Peptide Aggregation

Sensing of micro-to nanoscale samples in highly confined space is particularly important,and the ingenious design of solid-state nanopores has allowed the sensing of single nanoparticles,single molecules and single cells.Plasmonic sensors have a unique Raman enhancement activity,they can be combined with nanopore sensors to construct small and size-controllable plasmonic nanopores,which can detect ion current while achieving high signal-to-noise ratio of analyte spectra signal and realize single-molecule detection.In this thesis,a facile chemical reduction method was utilized to synthesize plasmonic nanopores at the tip of the nanopipette,and the electrical and optical properties of the nanopores were studied.Based on electrical detection and surface enhanced Raman scattering（SERS）detection,we can directly study on the amyloidosis process of the Aβ1-42 peptide,which is associated with Alzheimer’s disease.The main content is divided into the following two parts:1.Synthesis of plasmonic nanopores at the tip of glass nanopipetteIn this chapter,we have tried the electron-beam evaporation,photochemical fabrication,and chemical reduction mentioned in the previously published articles to synthesize ideal plasmonic nanopores.The first two synthesis methods showed some shortcomings,and finally we chose simple chemical reduction method to synthesis plasmonic nanopores.By screening the conditions for the synthesis of plasmonic nanopores,we have found that with the reactant concentration of 50 m M HAu Cl₄,5m M Na BH₄ and the reaction time of 1.5 min,we have a high synthesis reproducibility and can obtain plasmonic nanopores of 40±10 nm pore diameter.Compared with the previous two methods,the plasmonic nanopore synthesized by the last method shows a higher Raman enhancement effect and the analytical enhancement factor（AEF）can reach 2.9×10⁵.Under the applied bias potential,the SERS signal of the analyte have been observed,indicating that the plasmonic nanopore synthesized by this method is promising for the single-molecule analysis,providing spectral information in addition to electrochemical information.2.Exploring the aggregation behavior of the neurodegenerative disease-related pathogenic protein—Aβ1-42 peptides through the plasmonic nanoporeUpon applying a bias potential across the plasmonic nanopore,we have collected the ionic current signal of Aβ1-42 monomer and oligomers transport events,respectively.The ratio between the blockade current fluctuation with the baseline current of Aβ1-42 oligomers were larger than that of Aβ1-42 monomer.This phenomenon could be explained by the volume exclusion effect.In addition,we also found that the transport time of Aβ1-42 oligomers was longer than that of monomer.Limited by the huge size of Aβ1-42 fibers with sub-mm or mm length,the transport event of fibers could hardly be obtained through a 20 nm diameter nanopore.Most electrical signal of fibers were resulted from collision between fibers and nanopores.We have observed dynamic SERS spectra of Aβ1-42 oligomers and fibers under a bias potential as well.By improving the preparation and experimental conditions of nanopores,it is expected that the different amyloid aggregates can be distinguished using SERS through principal component analysis.