Construction And Application Of Fluorescent Probes For Anthrax Marker And Tetracycline Based On CdTe Quantum Dots

Nowadays,the spread of pathogenic bacteria and the misuse of antibiotics have posed significant security risks to humanity.Therefore,timely tracking and detection of such harmful substances is essential.Currently,common methods for detecting harmful substances include liquid chromatography and gas chromatography,which are effective and widely used,but large instruments are costly and require complex operations.As a result,fluorescence detection has gradually gained attention,as it does not require expensive instruments or highly specialized operators,while also offering advantages such as high sensitivity,good accuracy,and low detection limits,which are in line with the fast-paced lifestyle of today’s society.However,most fluorescence probes currently available have single functionalities or single modes.To maximize their utility and make them more versatile and convenient to use,the development of multi-functional and multi-mode probes that can adapt to societal needs is necessary.In this paper,based on the above issues,a multi-functional probe for detecting anthrax biomarkers and tetracycline was synthesized through modifications of CdTe quantum dots（CdTe QDs）,as well as a dual-mode probe for fluorescence and colorimetric detection.The specific results are as follows:（1）Based on the difference in excitation wavelength upon coordination with different ligands,Eu³⁺-modified CdTe QDs(CdTe QDs-Eu³⁺)were synthesized as a dual-functional ratiometric fluorescent probes for the detection of tetracycline（TC）and anthrax biomarker2,6-pyridinedicarboxylic acid（2,6-pyridindicarboxylic acid,DPA）in different excitation channels.Eu³⁺initially coordinates with the carboxyl groups on the surface of CdTe QDs,causing the aggregation of CdTe QDs and inducing fluorescence quenching.However,the addition of DPA and TC sensitized the red emission of Eu³⁺and further led to fluorescence quenching of CdTe QDs through fluorescence inner-filter,static and dynamic quenching.Interestingly,the excitation wavelengths of Eu³⁺after coordination with DPA and TC were275 nm and 386 nm,respectively.Based on this,dual-functional ratiometric detection of DPA and TC was achieved using different excitation channels.CdTe QDs-Eu³⁺exhibited rapid response（DPA-1 min,TC-1 min）and high sensitivity（DPA-LOD 0.3μM,TC-LOD2.2 n M）for DPA and TC detection.Furthermore,CdTe QDs-Eu³⁺was applied for the analysis of DPA and TC in food,biological,and environmental samples,obtaining satisfactory recoveries（80.0-119.0%）and relative standard deviations（0.5-8.4%）.（2）Based on the coordination interaction with Cd²⁺,xylenol orange（XO）was modified onto CdTe QDs to synthesize a fluorescence/colorimetric dual-mode probe for DPA detection.After modification of XO onto CdTe QDs,the red fluorescence of CdTe QDs was quenched due to fluorescence resonance energy transfer,while the coordinated XO exhibited a red color.Upon addition of DPA,the competition coordination of DPA and XO with Cd²⁺caused the release of XO from CdTe QDs,which interrupted the energy transfer and restored the red fluorescence of CdTe QDs,while the released XO exhibited a yellow color.Therefore,this phenomenon was used as a fluorescence/colorimetric dual-mode probe for rapid（1 min）detection of DPA.The experimental results showed that the probe achieved quantitative detection of DPA in the range of 0.1-5μM and 0.5-40μM by XO-CdTe QDs fluorescence mode and colorimetric mode,respectively,with detection limits of 42 n M and 240 n M.In addition,satisfactory relative standard deviations（fluorescence mode:0.1%-10.2%,colorimetric mode:0.8%-1.8%）and recoveries（fluorescence mode:100.0%-115.0%,colorimetric mode:86.0%-96.6%）were obtained for the determination of DPA levels in urine using XO-CdTe QDs.（3）A ternary composite CdTe QDs-Eu³⁺-EBT was synthesized using the metal indicator Eriochrome Black T（EBT）,Eu³⁺,and CdTe QDs for fluorescence/colorimetric dual-mode detection of TC.Eu³⁺can bind to the carboxyl group on the surface of CdTe QDs based on coordination,and can also bind to EBT,resulting in the ternary composite material.CdTe QDs-Eu³⁺-EBT exhibited green fluorescence under UV light,and the coordination between Eu³⁺and EBT resulted in a magenta color under sunlight.With the addition of TC,Eu³⁺was sensitized to emit red fluorescence by coordination,and TC replaced EBT through competitive coordination,resulting in the blue color of the solution due to the separation of EBT from Eu³⁺.The CdTe QDs-Eu³⁺-EBT achieved ratio fluorescence detection of TC in the concentration range of 0.5-20μM with a detection limit of 2.5 n M,and colorimetric detection of TC in the concentration range of 0.1-30μM with a detection limit of 0.5μM.Furthermore,the probe was applied to the detection of TC in urine,and satisfactory recovery rates（fluorescence mode:88.7%-110.0%,colorimetric mode:80.0%-100.0%）and relative standard deviations（fluorescence mode:1.2%-2.9%,colorimetric mode:1.9%-3.4%）were obtained.