Optical Characterization And Application Of Fluorescent Nanomaterials With Single Molecule Fluorescence Imaging

Fluorescent nanomaterials have attracted great attention in recent years due to their unique and excellent optical properties,and their optical properties have played a significant role in bioimaging,targeting markers and molecular testing.Recently,the study about the optical properties are focused on traditional optical characterization method,however,this kind of methods can only obtain the average results of the ensemble,covering many of the optical properties,such as blinking.Single molecular fluorescence imaging has its unique advantages,which can be used to study the optical behavior and heterogeneity of single fluorescent nanomaterials,and contribute to the study of photoluminescence mechanism and new applications of nanomaterials.In this thesis,we have investigated systematically the fluorescence properties of two types of nanomaterials,carbon dots(CDs)and semiconductor quantum dots(QDs)at single particle level using single molecule fluorescence imaging technique.The fluorescence heterogeneity due to the uneven size distribution of nanomaterials was discussed.We found that the results as following:1)At single particle level both QDs and CDs had fluorescence blinking behaviors but exhibited different blinking statistics.QDs had high single particle brightness and blinking statistics with large “on” state distributions up to 100 seconds,whereas CDs displayed burst-like blinking phenomenon with long-duration dark states up to tens of minutes,only having the longest “on” state less than 10 seconds.Single particle studies further showed that because of the uneven size distributions CDs exhibited a large spectral heterogeneity.For those particles with the mean diameter of about 4.5 nm,single particle fluorescence imaging with high quality can obtained by using 532 nm laser irradiation in combination with 590 nm long-pass emission filter.2)Based on the blinking behaviors of CDs with long-duration dark states,we developed a super-resolution imaging method by capturing fluorescence image sequences for sequential localizations of single particles in an optical diffraction-limited region.The imaging resolution can be achieved down to 25 nm.This super-resolution imaging technology without need of using two high-power laser excitations is much simpler than the existing methods such as Photo-activated Localization Microscope and Stochastic Optical Reconstruction Microscope.3)Finally,despite high single particle brightness and long-lived “on” states,the fluorescence blinking behaviors of singe QDs were strongly influenced by metal ions in the surrounding environment,especially in the case of silver ions.Base on the quenching effect of silver ions on blinking QDs,we developed an ultra-sensitive detection method for silver ions in a solution with the detection limit down to 10-8 mol/L.This sensitive detection method therefore hold a great promise in both environmental and medical fields by probing metal ions in biological tissues or cells.