A New Aptamer Turn-on Fluorescence/SERS Dual Mode Analytical Platform For Ultratrace Urea Using Fe/N Doped Carbon Dots As Catalyst

This paper introduced that the research progress of surface-enhanced Raman scattering spectroscopy,fluorescence spectroscopy,and dual-mode analysis,and reviewed the development of aptamers and carbon dots,and the methods and applications of urea detection.Based on the excellent catalytic performance of iron-doped carbon dots and the dual-mode detection method,a new analysis method was established and applied in real life.The specific research work was as follows:In Tris-HCl buffer solution,ferrocene was used as a precursor and iron-doped carbon dots（FeC）were prepared by hydrothermal method.Both ferrocene and FeC catalyzed the oxidation of 3,3’,5,5’-tetramethylbenzidine（TMB）by H₂O₂,With the increase of FeC concentration,the oxidation products of TMB generated by catalysis increase.After adding the nucleic acid aptamer（Apt）,Apt and carbon dots formed a complex morphology,thereby suppressing the catalytic performance of carbon dots,making the system fluorescence signal was reduced.the catalytic ability of Fe-doped carbon dots to H₂O₂-TMB was inhibited,and the formation of TMBox was reduced,so the fluorescence/SERS intensity decreased.When the target molecule urea was added,based on the three-dimensional structure of Urea-Apt nucleic acid chain and its flexibility,the spatial structure formed by the extension of the nucleic acid chain in solution had a large contact area with urea,causing the carbon dots to change to a free state,and its catalytic activity was restored,leading to fluorescence intensity of the system gradually increases.At the same time,TMBox had good SERS activity.With the addition of silver nanoparticles,the SERS signal of the system linearly increased within a certain range.Based on the FeC-H₂O₂-TMB-Tris-HCl-Apt-Urea system in a fluorescence peak at 405 nm produced a linear relationship between the change in fluorescence intensity and urea concentration in the range of3.33-13.32 ng/L urea,and the detection limit was 1.12 ng/L.Using silver nanoparticles as the SERS substrate and TMBox as the SERS probe,the FeC-H₂O₂-TMB-Tris-HCl-Apt-Urea system SERS intensity change had a linear relationship with the urea concentration in the range of3.33-16.65ng/L urea and the detection limit was 1ng/L.At the same time,the FeC-H₂O₂-TMB system had also achieved dual-mode detection of a variety of target molecules,which can establish a new method for high sensitivity SERS and fluorescence coupled dual-mode determination of urea.The dual-mode analysis method not only retained the sensitivity of the fluorescence and SERS detection methods,but also coupled them to further improve the reproducibility and accuracy of the SERS method.