Design And Sensing Application Of Metal Nanoclusters-based Ratiometric Fluorescent Sensors

Metal nanoclusters are widely used in fluorescence detection probes due to their simple preparation,excellent fluorescence properties,good biocompatibility and diversity of surface functional groups.Traditional fluorescent probes based on fluorescence intensity change are susceptible to the influence of probe concentration,excitation efficiency,detection efficiency and poor selectivity,which may lead to errors in measurement results?for example,fluorescent materials may be oxidized,and the sensor material may undergo aggregation or pH changes to quench the fluorescence of the probe?.Moreover,the sensor changes in local environment are difficult to control in complex systems such as cells or micro-devices,which may lead to measurement deviation.Compared with single emission fluorescence sensor,colorimetric fluorescence probe provides a new method because it can reduce the influence of external factors such as excitation rate,detection efficiency,probe concentration,light shielding and so on.In this paper,we use different construction methods to combine metal nanoclusters with intelligent response function and fluorescent materials to prepare three different forms of dual-emission colorimetric fluorescent probes,such as solution,microsphere and film.The synthesized probe was subjected to a detection study.In Chapter 2,carbon dot?CDs?/copper nanoclusters?Cu NCs?dual emission colorimetric fluorescence probes were prepared by in situ synthesis in aqueous solution.The probes consist of CDs emitting blue fluorescence and Cu NCs emitting red fluorescence,which display two easily distinguishable fluorescence emission peaks at a single excitation wavelength.In addition,using the agglomeration-induced fluorescence enhancement characteristics of Cu NCs,it shows strong red fluorescence in polar organic solvents,adding water to the system,and with the increase of water content,the red fluorescence is quenched gradually,while the blue fluorescence remains constant.The response of continuous fluorescent color from red to blue was obtained under the stimulation of different water content.The detection limit for water sensitivity was very low?detection limit<0.02%v/v?,and the colorimetric change could be clearly observed by naked eyes.Therefore,the prepared CuNCs-based dual fluorescence emission nanomaterials can use their fluorescence intensity ratio?red/blue?to detect trace water in organic solvents visually by colorimetry.In Chapter 3,a large size and easy to separate dual fluorescence emission Cu NCs-SiO2@CDs colorimetric fluorescent microsphere probe was synthesized by self-assembly method.Because the red fluorescence emission of Cu NCs has obvious aggregation-induced fluorescence enhancement properties,its aggregation and dispersion state changes with the change of pH.When the pH value increased from4.0 to 7.2,Cu NCs gradually changed from aggregation to dispersion,and red fluorescence gradually decreased,while the blue fluorescence of CDs remained almost unchanged.Therefore,at different pH values,red fluorescence and blue fluorescence are compounded with different fluorescence intensity,and their fluorescence ratios are different.By observing the color change of the composite light,visual colorimetric pH detection can be realized.Subsequently,we applied it to bacterial metabolic detection.Bacterial metabolites at different stages can be used to explore the shelf life of food and other substances by monitoring the pH changes of bacterial metabolic system and the amount of bacterial reproduction.At the same time,it can also be used for bacterial metabolic imaging with high signal-to-noise ratio.In chapter 4,we design a dual emission colorimetric fluorescence sensing film for metal ion detection.Double fluorescence emission films were successfully prepared from chitosan,graphite nitride?g-C3N4?and gold nanoclusters?Au NCs?.The results show that g-C3N4 can not only be used as a fluorescent emitter,but also improve the mechanical and thermal stability of the films.On the basis of this film,Au NCs was adsorbed on the surface of chitosan film by electrostatic interaction,and double fluorescence emission film was prepared.Because the red fluorescence of Au NCs can be quenched by Cu²⁺while the blue fluorescence of g-C3N4 remains unchanged,the selective detection of Cu²⁺can be realized by using the results different from those of other ions.The ratio of the two fluorescence intensities is affected by the concentration of Cu²⁺.With the increase of the concentration of Cu²⁺,the fluorescence color changes from orange red to yellow,blue and finally blue.Therefore,the prepared dual fluorescence emission film can be used as a colorimetric test paper to visualize the detection of Cu²⁺concentration.In addition,the film can detect Cu²⁺with high sensitivity and selectivity,and has a low detection limit?10ppb?.We find that this dual emission colorimetric fluorescence sensing paper based on Au NCs is a simple and convenient method for detecting metal ions.