Gold And Silver Nanoparticles As Dark-Field Scattering Microscopy Imaging Probe And Its Applications In Pharmaceutical Analysis

Dark-field scattering microscopy imaging technique is a non-scanning optical imaging technique with a very high contrast,and has been widely used in biochemical analysis,reaction monitoring,vital process tracking and single-cell imaging.Noble metal nanoparticles,especially gold and silver nanoparticles(AuNPs and AgNPs)are commonly utilized as the light-scattering probes because of their unique localized surface plasmon resonance(LSPR)features,which endow them with excellent optical properties,such as strong UV-vis absorption and localized surface plasmon resonance scattering bands.Currently,monitoring chemical reactions has been the most common application of dark-field scattering microscopy imaging techenique,and it is undoubtedly of great significance to attempt to monitor different types of reactions which are difficult to monitor by other methods.Besides,in this field,there is still a little research involved in the reactions about drug.Thus,carrying out the related research work will help to broaden the application range of dark-field scattering microscopy imaging technique in pharmaceutical analysis.By means of dark-field microscopy(DFM),plasmon resonance energy transfer(PRET)has also been better used for the detection of molecules and ions,but its mechanism is unclear to date,including the requirement for distance,the possible electron transfer between donor and acceptor,and so on.In addition,there are no researches achieving the detection of two substances based on the off-on mode of PRET,so the application of PRET is somewhat limited.Therefore,the research work described in this paper is done form two sides: monitoring the chemical reactions which are related to drug by dark-field scattering microscopy imaging technique and establishing a recognition method for drug.The details are as follow:1.Real-time dark-field scattering microscopy imaging of the dynamic degradation process of sodium dimethyldithiocarbamate.Considering that the degradation of pesticides have brought about serious problems in food and environment and real-time monitoring the dynamic degradation process of pesticides could help understanding and defining their degradation mechanisms,herein we made real-time monitoring of the decomposition dynamics of sodium dimethyldithiocarbamate(NaDDC)in neutral and alkaline conditions by imaging single AgNPs through darkfield scattering microscopy imaging;the LSPR scattering signals were measured at single nanoparticle level.As a result,the chemical mechanism of the degradation of NaDDC in netrual and alkaline conditions was proposed,and the inhibition effects of metal ions including Zn(II)and Cu(II)were investigated in order to understand the decomposition process in environments.It was found that Cu(II)can form a most stable complex with NaDDC with a stoichiometric ratio of 1:2,which greatly reduces the toxicity.2.Visualizing photoinduced electron transfer process on single silver nanoparticles.Understanding the photoinduced electron transfer(PET)mechanism is vital to improving the photoelectric conversion efficiency for solar energy materials and photosensitization systems.Herein we visually demonstrated the PET process by realtime monitoring the photoinduced chemical transformation of para-aminothiophenol(p-ATP),an important surface enhanced Raman spectroscopy(SERS)signal molecule,to 4,4'-dimercaptoazobenzene(DMAB)on single AgNPs with a LSPR spectroscopy coupled dark-field microscopy.The bidirectional LSPR scattering spectral shifts bathochromically at first and hypsochromically then,which were caused by the electron transfer delay of p-ATP,disclosed the PET path from p-ATP to O2 through AgNPs during the reaction,and enabled us to digitalize the corresponding electron loss and gain on the surface of AgNP at different time periods.This visualized PET process could provide a simple and efficient approach to explore the nature of PET,and might serve as a theoretical guide for drug synthetic reactions which involves PET.3.Recognition of acetylcysteine based on the off-on mode of PRET between the polyethyleneimine(PEI)modified gold nanorods(AuNRs)and Cu(II).The complex of PEI and Cu(II)has strong absorption at 634 nm,and the characteristic scattering peak of some AuNRs is at around 630 nm,which meet the requirement of PRET.Therefore,by modifying the AuNRs with PEI molecules by electrostatic adsorption,the recognition of copper ions can be achieved by the scattering quenching of PEI-AuNRs caused by the PRET between Cu(II)and PEI-AuNRs.The common drug acetylcysteine can reduce Cu(II)to Cu(I)and destroy the complexation of PEI and copper ions,so that the copper ions escape from the AuNR surface and the scattering light of PEI-AuNRs recovers.Therefore,a recognition method for acetylcysteine is established.Generally speaking,in this paper,we utilize AgNPs as probe to visualize and analyze the chemical reactions which are difficult to be analyzed by ordinary methods(pesticide degradation and PET process)through the dark-field scattering microscopy imaging technique,and deduce the reaction mechanisms;in addition,we also achieve the recognition of acetylcysteine by using the off-on mode of PRET between PEIAuNRs and Cu(II),broadening the application of dark-field scattering microscopy imaging technique in reaction monitoring and pharmaceutical analysis.