Construction Of Ratio Fluorescence Sensor Based On Carbon Quantum Dots And Its Application In Environmental Detection

In recent years,fluorescence analysis based on fluorescence CQDs has been widely used in biomedicine,environmental monitoring and other fields because of its high sensitivity,fast and simple.Based on CQDs,four kinds of fluorescence probes were prepared for the fluorescence detection of CIP,NO₃^–,PO₄^3–,AA and Ce⁴⁺:1.Using glucose as carbon source,CQDs were prepared by hydrothermal method.Combined with the dual advantages of rare earth complex and ratio fluorescence sensor,CQDs/Eu³⁺ratio fluorescence sensor with high sensitivity was constructed for CIP detection.Under excitation at 395 nm,CQDs/Eu³⁺has a strong blue fluorescence peak at 459 nm,and a weak red fluorescence peak at 616 nm.When the CIP exists,the fluorescence intensity of CQDs at 459 nm is enhanced based on charge transfer and hydrogen bond interaction.The experimental conditions of CQDs and Eu³⁺ratio,response time and stability were optimized.The results showed that:The ratio fluorescence sensor has a specific ability to identify CIP,and the fluorescence intensity ratio(F₄₅₉/F₆₁₆)has a good linear relationship with different concentrations of CIP（0～7μM）,and the minimum detection limit of CIP is 0.3μM,which is successfully used for accurate and sensitive detection of CIP.2.The Ui O-66-NH₂@Y-CQDs ratio fluorescence sensor was constructed by combining Ui O-66-NH₂ emitting blue fluorescence with Y-CQDs emitting yellow fluorescence by hydrothermal method,which was used for highly selective NO₃^–detection.The optical properties of Ui O-66-NH₂ were characterized by XRD,FT IR,SEM and TEM.When NO₃^–concentration changes,the fluorescence of Ui O-66-NH₂ is enhanced due to the weakening of LMCT effect.In addition,the effect of NO₃^–and Y-CQDs promoted charge transfer,leading to the fluorescence quenching of Y-CQDs,which changes the intensity of blue fluorescence at 413nm and yellow fluorescence at 564 nm were enhanced and weakened with the increase of NO₃^–concentration,respectively.The results show that:Under optimal conditions,F₄₁₃/F₅₆₄ showed a good linear relationship with NO₃^–in the concentration range of 1～10μM,with the lowest detection limit of 0.85μM.Moreover,the interference of some possible co-existing substances was investigated,which was successfully used for high sensitivity detection and selective identification of NO₃^–.3.High fluorescence CQDs were synthesized by hydrothermal method and encapsulated in ZIF-8.According to the SOS of ZIF-8 and the fluorescence of CQDs,CQDs@ZIF-8 ratio fluorescence sensor was constructed for the detection of PO₄^3–.The structure and morphology of the composite were analyzed by XRD,FT IR,SEM and TEM,and the fluorescence properties were analyzed by fluorescence spectrum.After adding PO₄^3–,it would react selectively with Zn²⁺in ZIF-8,resulting in the cracking of ZIF-8 to release CQDs,resulting in the fluorescence recovery of CQDs and the reduction of SOS intensity.The results show that the linear relationship between F₄₃₇/S₇₃₂ and PO₄^3–is good in the concentration range of 1～40μM under optimal conditions,and the lowest detection limit is 0.23μM.The interference of some possible co-existing substances has been investigated,and it has been successfully used for the rapid detection and selective recognition of PO₄^3–.4.N,S-CQDs and stable BSA-Au NCs were synthesized by hydrothermal method,and the N,S-CQDs@BSA-Au NCs ratio fluorescence sensor was constructed for the continuous determination of Ce⁴⁺and AA.When Ce⁴⁺was added,BSA-Au NCs were oxidized by Ce⁴⁺,which attracted BSA-Au NCs to aggregate into larger particles.The fluorescence of BSA-Au NCs was enhanced due to the AIE effect.Therefore,a"turn-on"near-infrared fluorescence sensor platform for Ce⁴⁺detection was constructed.Subsequently,when AA was added,Ce⁴⁺was desorbated on BSA-Au NCs surface due to its strong affinity for AA due to its strong oxidation,resulting in reduced fluorescence intensity.A Ce⁴⁺mediated N,S-CQDs@BSA-Au NCs"turn-off"type near infrared fluorescence sensing strategy was developed to detect AA.The results show that the ratio fluorescence sensor based on the"off-on-off"detection mechanism has a good linear relationship between F₄₂₉/F₆₉₂ and Ce⁴⁺concentration under optimal conditions,and the lowest detection limit is 0.12μM.N,S-CQDs@BSA-Au NCs/Ce⁴⁺added AA,F₄₂₉/F₆₉₂ also showed a good linear relationship with different concentrations of AA in the range of 1～10μM,and the lowest detection limit was 0.19μM.The interference of some possible co-existing substances was explored to realize the selective recognition and rapid detection of Ce⁴⁺and AA by the ratio fluorescence sensor.