Research On The Optical Activity,metal Ion Sensing And Application Of CdTe Quantum Dots Based On Multiple Spectral Analysis

Quantum dots（QDs）are a class of semiconductor nano-fluorescent materials with excellent optical properties,which are widely used in many fields.As fluorescent nano-sensors,they have received extensive attention in the field of analytical chemistry.Quantum dots themselves have complex optical properties.They are not only photon absorbers,but also photon emitters and scatterers.Their optical behavior cannot be fully and accurately described by traditional fluorescence spectroscopy techniques.The use of Cd Te quantum dots as sensors can facilitate the sensing of trace metal ions and has important practical value,but the sensing mechanism of quantum dots for metal ions is still controversial.In this work,multiply spectral analysis techniques are employed to investigate the the optical behavior of Cd Te QDs;and then the mechanism of Cd Te QDs sensing metal ions was discussed from the perspective of scattering and fluorescence polarization;finally,the application of Cd Te QDs in the detection of trace metal ions is introduced.The details are as follows:（1）The optical activity of Cd Te quantum dots was studied using polarization simultaneous resonance spectroscopy（PRS2）technique in combination with conventional UV-visible absorption spectroscopy（UV-vis）and Stokes fluorescence spectroscopy（SSF）,focusing on the effects of ligands,concentration,incubation time and solvent polarity on their optical properties.The results show that Cd Te quantum dots with different fluorescence colors can be easily prepared by wrapping different ligands,and it is more convenient to wrap different ligands than to adjust the temperature and time for synthesizing Cd Te quantum dots.The photochemical properties of the prepared quantum dots are relatively stable due to the electrostatic protection of the ligands,but are easily affected by the polarity of the solvent.As the polarity of the solvent decreases,it leads to a decrease in the solubility of quantum dots and quantum dot agglomeration,which further induces fluorescence quenching.The scattering spectra,resonance fluorescence spectra,scattering cross sections,resonance fluorescence cross sections,and scattering extinction ratios of the quantum dots were calculated using the PRS2 technique.The results show that the scattering cross section of quantum dots is larger compared with organic dyes and cannot be neglected.（2）Study of metal ion sensing by Cd Te quantum dots using scattering and fluorescence polarization.It was found that Hg²⁺can lead to fluorescence quenching of Cd Te quantum dots,fluorescence peak redshift and fluorescence polarization anisotropy increase,and the same phenomenon is also observed in Ag⁺,Cu²⁺,Pb²⁺,Sn²⁺,Co²⁺,Fe²⁺,Ni²⁺and Mn²⁺plasmas.Ca²⁺,K⁺and Mg²⁺had little effect.Analysis of the scattering spectrum shows that Hg²⁺,Ag⁺,Cu²⁺,Pb²⁺,Sn²⁺,Co²⁺,Fe²⁺,Ni²⁺,Mn²⁺interact with Cd Te quantum dots obviously,resulting in agglomeration and even deposition.According to the K_sp of sulfide,these metal ions can form insoluble salts with S element,and it is speculated that they may combine with S atoms on the ligand,resulting in the change of the surface charge density of Cd Te quantum dots,the activation of lattice surface defects,and finally the fluorescence attenuation or quenching.In addition,the combination of these metal ions with Cd Te quantum dots destroys the electrostatic repulsion force on the surface of Cd Te quantum dots,leading to agglomeration,discrete energy levels into continuous energy levels and fluorescence quenching.However,Ca²⁺,K⁺and Mg²⁺cannot form insoluble salts with S element,so they have little influence on the luminescence behavior of Cd Te quantum dots.（3）The fluorescence quenching system of Tin-GSH modified Cadmium telluride quantum dots was constructed by using quantum dot fluorescence quenching method to determine tin content.The experimental conditions of the system were optimized and a method for the determination of tin in food was established.The results showed that the fluorescence quenching degree of Cd Te quantum dots showed a good linear relationship with the concentration of Sn⁴⁺,and the linear range was 0.05～0.3μg/m L.The linear regression equation is（I₀-I/I₀）=2.9817 c-0.0231,the linear correlation coefficient is R~2=0.998,the detection limit was 0.0098μg/m L,and the relative standard deviation is1.69%.GSH modified quantum dots have a wide linear range and high sensitivity for Sn⁴⁺detection,and can be used for the detection of Sn⁴⁺at a certain concentration.This method is sensitive,simple to operate,and reliable,and can be used for the determination of trace tin in sewage and canned food.