Design Of Ratiometric Fluorescent Probes And Its Applleation In The Detection Of Small Biological Molecule

Ratiometric fluorescence probes,a combination of two different fluorescent emission peaks,to detect a specific target.Compared with the single emission fluorescence probe,the ratiometric probe has the advantage of being able to eliminate the influence of the external environment,the error caused factors of concentration of the probe molecule itself.At the same time,the probe has high sensitivity and selectivity,which obtains more accurate experimental results.For the metal ions and small biological molecules,the study provides great convenience and has important applications in environmental monitoring,biochemical sensing,life sciences,a plurality of immunoassay and other fields.In order to improve the detection,selectivity and visual detection ability of the ratiometric fluorescence probe in biological small molecules,two kinds of fluorescent probes were designed and synthesized by using semiconductor quantum dots.?1?We designed and synthesized a novel nano composite ratiometric fluorescence probe?CdSe@SiO₂@CdTe?for the detection of ascorbic acid?AA?.The nanohybrid probe was made up of red-emitting CdTe quantum dots?QDs?covalently linked onto the surface of silica nanoparticles embedded with green-emitting CdSe QDs.The red fluorescence of the outer CdTe QDs was first quenched upon addition of KMnO₄ via a chemical oxidation process.In the presence of AA,the red fluorescence was switched to the“on”state due to the reduction of CdTeO₃/TeO₂ to CdTe on the QDs surface,whereas the inner green fluorescence of CdSe QDs remained constant.Consequently,an obviously distinguishable fluorescence color variation?from green to orange-red?of the probe solution was observed.Under the optimal conditions,the ratiometric of the intensity from the QDs fluorescence at 616 nm to that at 522 nm showed an excellent linear correlation with the concentration of AA ranging from 0.1to 5.0?M,and a detection limit as low as 50 nM was achieved.Furthermore,the ratiometric sensor was successfully employed for the analysis of AA in fruit juice samples with satisfactory results.?2?In addition,we have also designed a fast,highly selective and visualized ratiometric fluorescence probe?CdSe@SiO₂@CdTe?to detect reduced glutathione?GSH?.Unlike work?1?,the modifier for the outer cadmium telluride quantum dots is changed to N-acetyl-L-cysteine?NALC?.Upon the addition of Hg²⁺,the red fluorescence of the outer CdTe QDs was quenched through both electron transfer and ion-binding processes.In the presence of glutathione?GSH?,the red fluorescence occurred again due to the strong affinity between GSH and Hg²⁺,whereas the inner green fluorescence of CdSe QDs remained constant,resulting in an obviously distinguishable fluorescence color variation?from green to orange-red?of the probe solution.Under optimal conditions,the ratiometric of the intensity from the QDs fluorescence at 619 nm to that at 535 nm showed an excellent linear correlation with the concentration of GSH ranging from 0.1 to 10?M,and a detection limit as low as42 nM was achieved.Meanwhile,the quantum dot ratiometric hybrid probes were successfully applied for direct visual sensing GSH in real vegetable and fruit samples.