Synthesis Of GSH-AuNCs And Its Application In Fluorescence Sensing Analysis

Compared with the traditional organic fluorescent probes,fluorescent nanomaterials display lots of advantages,such as,adjustable morphology and particle size,superior photostability as well as easy surface functionalization,etc.Therefore,the application of fluorescent nanomaterials as optical sensors has become a research hotspot in many fields such as biomedicine,food engineering and environmental monitoring.However,the emission wavelength of most fluorescent nanomaterials is located in the UV-vis region.Due to the short-wavelength emission is subject to severe scattering and background interference,which greatly limits its application in the field of optical sensing.In contrast,near-infrared emission can significantly reduce the interference of Rayleigh and Raman scattering,and because biological natural molecules rarely emit fluorescence in this region,it can greatly avoid the interference of auto-fluorescence in complex samples.Thus,fluorescent probes based on near-infrared（NIR）emission are considered to be the most promising materials to improve the sensitivity of fluorescence sensing and imaging.In this paper,a gold nanocluster with good performance was prepared,and its fluorescence emission was located in the near infrared long wave region.Based on this,a series of sensing platform was constructed to realize the detection of NO₂^-、Fe³⁺and ascorbic acid.Chapter 1:The properties,preparation methods and characterization methods of gold nanoclusters were introduced,and their applications in optical sensing,imaging,medicine and other fields were reviewed.On this basis,the design idea of this paper was proposed.Chapter 2:GSH-AuNCs with good water solubility were synthesized by a simple one-step hydrothermal method using glutathione as modifier and reducer.The morphology,particle size,composition and optical properties of gold nanoclusters were analyzed by various techniques.The fluorescence spectra of the gold nanoclusters show that it has strong near-infrared fluorescence emission at 520 nm excitation wavelength,and the maximum emission wavelength is 798 nm.Further,based on the quenching effect of NO₂^-on the near-infrared fluorescence of GSH-AuNCs,a new method for the determination of NO₂^-was successfully established with the linear range of0.22-295.97μM and the detection limit of 0.0122μM.At the same time,the constructed near infrared fluorescence sensor was applied to the detection of NO₂^-in actual water samples,and satisfactory results were obtained.Chapter 3:The near-infrared（NIR）fluorescent probes are considered to be one of the most promising molecules for improving the sensitivity of fluorescence sensing and imaging.In this chapter,a novel“turn-off-on”sensing strategy was constructed based on near-infrared fluorescence of GSH-AuNCs for the sequential determination of Fe³⁺and AA.Firstly,the near-infrared fluorescence of GSH-capped gold nanoclusters（GSH-AuNCs）can be significantly quenched by Fe³⁺,and the fluorescence quenching mechanism is speculated to be dynamic quenching by studying the fluorescence lifetime.Then,the near-infrared fluorescence of GSH-AuNCs was recovered by adding ascorbic acid（AA）into the GSH-AuNCs/Fe³⁺mixture.The decrease and increase of NIR photoluminescence（PL）intensities of GSH-AuNCs were linearly correlated with the concentration of Fe³⁺and AA,respectively.Therefore,a turn-off-on NIR PL sensing strategy can be constructed for sequential detection of Fe³⁺and AA with the linear range of 0.7-180μM and0.5-120μM,respectively.The proposed NIR PL sensor exhibits excellent sensing performance and has been applied to the determination of Fe³⁺and AA inreal samples with satisfactory results.Chapter 4:Manganese dioxide（MnO₂）nanosheets have excellent absorptive capacity over a wide wavelength range and can be used as an effective fluorescence quenchers or energy receptor.In this work,a novel fluorescent sensing platform using gold nanoclusters（GSH-AuNCs）and MnO₂ self-assembled nanocomposites as fluorescent probes is designed for the detection of AA.The prepared MnO₂ nanosheets can effectively quenchthe near-infrared fluorescence of GSH-AuNCs and make the fluorescence turn-off of GSH-AuNCs/MnO₂ nanocomposites.AA has strong reducibility and can undergo redox reaction with MnO₂ nanosheets.Therefore,when AA was added into the GSH-AuNCs/MnO₂ nanocomposite system,the MnO₂ nanosheets were reduced and decompresented,resulting in near-infrared fluorescence turn-on of GSH-AuNCs.There is a good linear relationship between the degree of fluorescence recovery and the concentration of AA,the linear range was from 0.41 to 123.93μМwith a detection limit of 0.01μМin the fluorescence detection.Chapter 5:The application of sensors constructed by synthetic GSH-AuNCs in detection is summarized,and the direction we will strive for next is listed.