Single-particle Imaging Analysis Of The Light-matter Interaction Between Gold Nanobipyramids And Para-aminothiophenol

In recent years,with the development of nanotechnology,researches and knowledges on light-matter interaction at the nanoscale have considerably advanced and increased,and noble metal nanoparticles have become one of the most popular materials in the field of light-matter interaction due to their unique local surface plasmon resonance(LSPR)phenomenon generated by irradiation.Firstly,noble metal nanoparticles have tunable LSPR spectra under illumination,showing different colors of their colloidal solution,which can be used as probes for analyzing sensing and imaging.Moreover,the LSPR of noble metal nanoparticles under illumination produce hot carriers,photothermal and local electric field enhancement effect,which can affect the photo chemical behavior and photophysica processes of organic molecules adsorbed on the surface of metal nanoparticles,resulting the change of molecular spectra or plasmon resonance spectra and color of colloidal solution.With the development of single nanoparticle analysis technology,using single particle dark-field microscopy(DFM)and single particle scattering spectroscopy to study nanometer-scale light-matter interaction has gradually become a reseach frontier,which can overcome the shortcomings of averaging the analysis signals of assemblies in solution and highlight individual differences,improving the sensitivity and accuracy of analysis.Therefore,single particle dark-field microscopy(DFM)and spectroscopy have been widely used in fields such as monitoring the chemical reaction,nanofabrication of the nanocomposite material,biosensing,imaging,and so on.In the past decade,the most representative light-matter interaction of thiophenol derivatives on the surface of noble metal plasmonic nanoparticles have been further studied and applied in plasmon-enhanced spectroscopy,plasmon-driven photocatalytic reactions,and energy and charge transfer on the hybrid interfaces.At present,the aggregates of nobel metal nanoparticles were often utilized to obtain the surface-enhanced Raman spectroscopy of aromatic thiol molecules to explore the mechanism,and single-particle scattering imaging and spectra of noble metal nanoparticles were also used to analyze the mechanism.However,the mechanism of light-matter interaction of thiophenol derivatives on the surface of noble metal nanoparticles has always been controversial,and the interaction is easily affected by various physical and chemical factors in the surrounding environment,which increases the complexity of the plasmon-enhanced light-matter interactions of organic molecules.Therefore,fully understanding this complex light-matter interaction mechanism by using both of molecular spectroscopy and single particle scattering analysis in real time and in-situ remains a challenge.In fact,it is necessary to explore the light-matter interaction between light and nobel metal nanoparticles,the light-matter interaction between light and organica molecule from the single particle level,which is helpful for better understanding the mechanism of plasmon-enhanced light-matter interaction of organic small molecules on the surface of noble metal nanoparticle.These researches are of great significance for further development and application of plasmon-enhanced sensing and imaging probes.Therefore,considering the above problems and difficulties about light-matter interaction of thiophenol derivative on the surface of noble metal nanoparticles,the anisotropic gold nanobipyramids(Au NBPs)with high-purity and uniform size and organic nanoparticles formed by photochemical reactions of thiophenol derivatives in water media were choosen as single-particle dark-field scattering imaging probes,which were used to study the light-matter interaction mechanism of Au NBPs and para-aminothiophenol(p-ATP).Moreover,these studies were applied in analytical sensing,photo induced organic conversion and the nanofabrication of hybrid nanomaterials.1.The analysis and application of the scatting light color signal of the gold nanobipyramids.In recent years,with the continuous optimization of the synthesis method,Au NBPs with high purity,uniform size,and unique tip enhancement effect can be obtained easily.The solution of Au NBPs under illumination has unique LSPR spectrum and different colors,which can be adjusted with the change of the aspect ratio of Au NBPs,making it become one of the most popular plasmonic sensing probes.Currently,single-particle analysis of Au NBPs is mainly based on the single-particle scattering spectrum.However,single-particle scattering imaging color signals of Au NBPs that are simpler and easier to obtain are often ignored.Therefore,in this work,Au NBPs with different aspect ratios were synthesized for exploring the dependence of the DFM imaging color on the aspect ratio,size,particle coupling,structural anisotropy and the direction of the Au NBPs,which were further applied to monitore the morphological changes accompanying with gold amalgamation reaction.Moreover,the polarized light scattering imaging of Au NBPs was used to monitor the anisotropy of the surface reaction under polarized light at single-particle level.The results showed that the dark-field light scattering imaging color of Au NBPs were mainly red,and as the aspect ratio increases,the color changed from red to orange-red and yellow.The red Au NBPs were selected as single-particle light scattering imaging probes to study the gold amalgamation reaction caused by ascorbic acid and Hg²⁺.It was found that the reaction in the dark-fied microscope was stronger than the solution reaction.Firstly,the tip of the Au NBPs reacted with Hg,then the morphology of Au-Hg nanoalloys gradually changed from bipyramids to rice grains and sphere,and the color of scattering light changed from red to orange,yellow,green,cyan,and blue.Therefore,a simple and rapid analysis method for detecting Hg²⁺was established according to the rainbow colors of Au-Hg nanoalloys.In addition,the scattering imaging color of Au NBPs under polarized light irradiation also depended on the direction of the Au NBPs.When the incident polarized light was perpendicular or parallel to the longitudinal axis of the Au NBPs,the color of Au NBPs shown green and red respectively.So,the polarized light scattering color of Au NBPs can be used to sense the orientation of Au NBPs simply,which can also be used to monitor the anisotropy reaction on Au NBPs surface under polarized light irradiation in real time.2.Monitoring the photo-oxidation coupling of para-aminothiophenol in an aqueous environment in real time by dark-field microscopy imaging.The chemical transformation under visible light irradiation is of great significance in green preparation.Here,the photo-oxidative coupling reaction of para-aminothiophenol(p-ATP)was realized by the catalyst-free visible light illumination in an aqueous environment.The results of normal Raman spectra and high-resolution mass spectra showed that photooxidation coupling reaction of p-ATP aqueous solution in the absence of photocatalyst or plasmonic nanoparticles forms 4-aminophenyl disulfide(APDS)rather than 4,4'-dimercaptoazobenzene(DMAB),indicating that sulfhydryl group was more likely to react to form S-S bond than amino group to react to form azo bond under light irradiation,which was very different from the plasmon-assisted photocatalytic model reaction of p-ATP to DMAB.Due to the poor water-solubility of disulfide,monodisperse uniform organic nanoparticles were formed in situ,which has strong light scattering signal,so the DFM imaging technology can be used to monitor the formation of disulfides in real-time and in situ at the single particle level.Experiments shown that water and irradiation were necessary conditions for the photo-oxidation coupling of p-ATP to form disulfides,and irradiation time,irradiation power density,acidity,and dissolved oxygen in water could affect the formation of disulfides.Moreover,it was found that the formation of disulfides through photooxidative coupling reaction of thiophenol derivatives proceeded successfully regardless of electron-donating or electron-withdrawing substituents in the para positions.The ultrafast transient absorption(TA)spectra and electron paramagnetic resonance(EPR)spectra verified that the para-aminophenylthiyl radicals was important intermediate produt in the light-induced disulfide formation.This reseach provides important guidelines for the green synthesis of disulfides and provides new ideas for real-time in situ monitoring of visible light-induced organic conversion at the single particle level using DFM.3.Plasmon of gold nanobipyramids-accelerated photodimerization of thiophenol derivatives for nanofabrication of metal organic hybrid nanoparticlesThe nanoscale light-matter interactions of aromatic thiols on the surface of plasmonic nanoparticle has received widespread attention in the plasmon-enhanced spectroscopy,plasmon-driven catalysis reactions and energy and charge transfer at hybrid interfaces,most of which are based on the chemisorbed thiophenol derivatives self-assembled monolayer through gold/silver–thiol bond and subsequent photochemical and photophysical processes.Here,we used plasmon-accelerated photo-induced dimerization reaction and subsequent photoinduced crystallization process of p-ATP and p-NTP on the surface of Au NBPs in aqueous solution to synthesize plasmonic hybrid nanoparticles with concentric core–shell,eccentric core–shell,and Janus structure.By using the DFM coupled LSPR scattering spectroscopy and co-location technology of DFM image and SEM images,the photo-induced disulfide reaction of thiophenol derivatives on the surface of Au NBPs was monitored and the growth process of the core–shell hybrid nanostructure was recorded in situ at the single nanoparticle level.The results shown that the morphology and thickness of eccentric core-shell,concentric core-shell and Janus structures can be controlled by adjusting the concentration of p-ATP aqueous solution,irradiaion time and irradiation intensity.It was demonstrated that the chemical interface damping of longitudinal surface plasmon resonances of Au NBPs was greatly enhanced that up to 90%efficiency with self-assembled multilayer diaryl disulfides.Moreover,the highly enhanced transverse plasmon resonance of single plasmonic hybrid nanoparticle was also obtained with a sufficiently thick organic shell,which was different from the previous research about light-matter reaction of p-ATP and p-NTP to photodimerization to DMAB or chemical interface damping(CID)as self-assembled monolayer on the surface of gold nanoparticles.These results are important for understanding the complex light-matter interactions of aromatic sulfide and disulfide on the surface of noble metals to improve the plasmon-catalysis energy conversion efficiency and selectivity of photo-induced organic transformations and for designing novel plasmonic hybrid nanocomposite with desired structure,optical properties,and functions.In summary,this study focuses on the light-matter interaction between light,Au NBPs,and p-ATP.The dark-field light scattering imaging signals of Au NBPs,organic nanoparticles,and metal-organic hybrid nanoparticles were used for screening of light scattering imaging probes and monitoring the reaction process at a single nanoparticle level.These reactions have been successfully applied to the fields such as the establishment of the Hg²⁺analysis and sensing platform,the discussion and understanding of the mechanism of photoinduced disulfide formation,the nanofabrication of concentric,eccentric core-shell and Janus metal-organic hybrid nanostructures with controllable morphology and the regulation of LSPR spectra of plasmonic hybrid nanoparticles.The plasmon generated by the interaction betweeen light and Au NBPs enhanced the reduction reaction of Hg²⁺with ascorbic acid on the surface of Au NBPs and promoted the occurrence of gold amalgamation.Moreover,the photooxidation reaction of p-ATP was also enhanced by the plasmon.At the same time,the reaction anisotropy under polarized light irradiation on the surface of Au NBPs have been realized and utilized for site selective growth.These works provide new strategy for studying the light-matter interaction of organic molecules on the surface of metal nanoparticles and extending their applications at the single particle level.