Application Of Single Silver Nanoparticle As Dark Field Imaging Probe In Study Of Photochemical Reaction And Light Scattering

The light scattering is a common optical phenomenon in the nature.The nanoparticles have the property of light scattering.The advantages of nanoparticles such as strong optical signal,good stability,adjustable band of scattered light and easy marking lay a solid foundation for them to be an excellent optical scattering probe.The dark field microscopy imaging technique has the advantages of no background and high signal-to-noise ratio during studying or detecting the target due to its oblique illumination incident mode,which most technologies are unbeatable.Therefore,the dark field microscopy imaging technique can not only be used to study the properties of resonant scattering light of nanoparticles,but also delve into some dynamic processes of physics or chemistry in real time at the single nanoparticle level,which make metal nanoparticles become more excellent imaging probes.The combination of dark field microscopy imaging technique and nano materials with excellent optical properties can expand the application scope of the instrument,and also make the application prospect of nano materials more broad.However,there are still some limitations in studying the optical properties and applications of nanomaterials at the single particle level by using dark field microscopy.For example,studying the properties of resonant light scattering of individual nanoparticle and the diversity of probes is still not perfect,and the real-time dynamic analysis process is not intensively studied.Based on this,the following researches are carried out in this paper from the aspects of exploring new dark field light scattering probes,in-depth study of resonance scattering properties of single particle and real-time dynamic process.1.In situ investigating the size-dependent scattering signatures and sensing sensitivity of single silver nanocube through a multi-model approach.Insightful understanding of size-dependent optical signatures and precise regularity of nanosensors is critical for developing applications of plasmonic sensing.This work presents a systematic study on localized surface plasmon resonance(LSPR)-based nanosensors of plasmonic silver nanocubes(Ag NCs)with the edge lengths of 59.84 ±7.97 nm(no.1 Ag NCs),75.70 ± 9.05 nm(no.2 Ag NCs)and 110.32 ± 14.63 nm(no.3Ag NCs),respectively.The effects of different sizes on the scattering signatures and refractive index(RI)sensitivities of Ag NCs were in situ determined using the multi-model co-localization approach of single Ag NC by dark-field microscope(DFM),LSPR spectroscopy and scanning electron microscopy(SEM).The scattering light colour of single Ag NC took place bathochromic shift from monocolour to multicolour with the growth of edge length of single Ag NC.The LSPR scattering spectra of no.1and 2 Ag NCs exhibited singlet and singlet with the shoulder peak from quadrupolar resonance mode,respectively.Compared with the scattering signatures of no.1 and 2Ag NCs,the interesting LSPR effect of plasmon line shape with two distinct peaks was observed on single no.3 Ag NC.In situ studies on the scattering spectral response of single Ag NC to the ambient solvents and probing the small-molecule adsorbates on the surface of single silver nanocube reveal that no.2 Ag NC is more suitable as nanosensor due to strong regularity and higher sensitivity.2.Microscopically monitoring chemical reaction of plasmon-driven photocatalytic proton coupled electron transfer on a single silver nanoparticle.By using a local surface plasmon resonance(LSPR)spectroscopy coupled dark-field microscopy to visually monitor the LSPR scattering properties of a single silver nanoparticle(Ag NP)and microscopically count the electrons gain and loss,herein we identify that the plasmon-driven photocatalytic reaction(PPR)process of4-nitrothiophenol(4-NTP)dimerizing into 4,4'-dimercaptoazobenzene(DMAB)is proton coupled electron transfer(PCET)dependent,during which alternation at first and then simultaneity of electrons gain and loss occur.In addition,in order to further prove the imbalance of electron gain and loss and hot electron transfer during PPR,we carried out a series of experiments,namely,the change of extinction spectra in plasmon-driven photocatalytic dimerization of 4-NTP into DMAB in the whole solution;the photoelectric response and cyclic voltammetry of silver nanoparticles before and after PPR;the transient absorption experiments.These experimental data strongly prove the change of LSPR light scattering properties of optical nanoprobes and the electrons gain and loss in the process of PPR.This finding of both PCET and time-dependent alternation-simultaneity of electrons gain and loss in the PPR of 4-NTP can furnish exciting new opportunities for improving efficient light-to-energy and photoelectric conversions,showing that microscopic electron counter can be developed with a single plasmonic nanoparticle in the research of heterocatalysis and photoelectric conversion and other nanocatalytic processes involving electron transfer through a LSPR spectroscopy coupled dark-field microscopy.3.The mesoscopic anti-galvanic reaction of mercury(?)was studied at the level of a single silver nanoparticle with dark field microscopy.The green with blue and yellow but impure silver nanocubes were used as light scattering probes to study and analyze the mesoscopic anti-galvanic reaction of mercury(?)at the single nanoparticle level in real time.The experimental results show that between the range of macro and less than 10 nm,the mesoscopic anti-galvanic reaction of silver and mercury(?)can occur.The fastest reaction time was 1 min,and the scattered light of silver nanoprobe is blue shifted,which provides a new mechanism for the detection of highly toxic mercury(?),and lays a theoretical and experimental foundation for the development of rapid single particle detection platform.In this paper,we synthesized silver nanoparticles of different size and shape.The light scattering imaging of single cubic and spherical silver nanoparticles was realized using the dark field microscope system.Thus,the optical properties and sensing sensitivity of single silver nanocube were systematically studied;the continuous process and the change of optical scattering properties of spherical nanoparticle in plasmon-driven photocatalytic dimerization of 4-NTP into DMAB on a single silver nanoparticle were visually monitored.Finally,the appropriate nanoprobes were selected and applied to study the mesoscopic anti-galvanic reaction of mercury(?).These are of great significance for screening optical probe from monocolour to multicolour,further researching the intermediate process and the nature of electron transfer of chemical reaction,and the establishment of single particle rapid analysis and detection platform.