Synthesis And Characterization Of Magnetic Resonance/ Fluorescent Dual-mode Contrast Agents And Application In Biological Analysis

Accurate medical diagnosis and treatment require sensitive and accurate imaging techniques.The multimodality imaging probe has become a powerful tool to improve the detection sensitivity and accuracy,which is of great significance in the diagnosis and treatment of diseases.By combining difference imaging technologies,multimodality imaging has become an important way to overcome the shortcomings of single imaging methods,achieve greater penetration depth and higher resolution of non-invasive imaging,as well as more accurate diagnosis and higher sensitivity requirements.Based on this,the synthesis,characterization and application of nanoprobes with fluorescence and magnetic resonance were discussed.The details are as follows:1.Using glutathione?GSH?as carbon source,EDTA as metal ion stabilizer and FeSO₄�7H₂O as Fe²⁺raw material,Fe-CQDs with both magnetic resonance and fluorescent properties were prepared by simple one-pot hydrothermal method.The mixed solution of GSH,EDTA and FeSO₄�7H₂O was heated at 180 ^oC for 6 h.After the reaction,a transparent red-brown solution was obtained.Fe-CQDs were obtained after natural cooling and dialysis for 24 h.The kinds of the doped metal ions,the proportion of the reaction materials and the reaction time were optimized.The condition-optimized results show that the highest 1/T₁value is displayed at 180 ^oC reaction 6 h and the molar ratio of GSH/EDTA/FeSO₄�7H₂O is5/2/1.Fe-CQDs was further characterized by TEM,EDS,XPS and FTIR.The results show that Fe²⁺is successfully doped in carbon quantum dots.2.The prepared Fe-CQDs has a longitudinal relaxivity of 3.92 mM^�1?s^�1 and a transverse relaxivity of 4.99 mM^�1?s^�1,indicating that Fe-CQDs is superior to the clinical Gd-based contrast agent(r₁?3.1-3.5 mM^�1?s^�1).The approach of r₂/r₁ to 1 also implies that Fe-CQDs have potential as an efficient T₁-weighted contrast agent.At the same time,Fe-CQDs retains the efficient optical properties of carbon quantum dots,and the quantum yields is 3.80%.Moreover,Fe-CQDs has good optical stability and extensive pH adaptability.It shows that Fe-CQDs has potential application in bioimaging.3.The results of cell viability test,in vivo growth assessment and histochemical assessment showed that Fe-CQDs had negligible cytotoxicity and did not cause severe tissue damage or inhibit the growth of mice,indicating that Fe-CQDs had excellent biocompatibility.In vitro experiments on A549 cells showed that Fe-CQDs had specific internalization in cells and retained the fluorescence and magnetic resonance characteristics of Fe-CQDs.Therefore,Fe-CQDs can be used for magnetic resonance and fluorescence dual-mode bioimaging,and it has the potential to accurately provide physiological and spatial information of the target tissue.In vivo experiments,Fe-CQDs showed high contrast efficiency and improved the positive contrast signals of T₁-weighted images.In addition,time-dependent in vivo magnetic resonance imaging of the major organs revealed that Fe-CQDs exhibited rapid glomerular filtration and eluding immune absorption due to its ultrasmall size and good biocompatibility.These results indicate that Fe-CQDs has the potential to be used as fluorescent and magnetic resonance dual-mode bioimaging probes.The dual-mode imaging probe is very helpful for the early diagnosis of many diseases.4.Fe-CQDs was used for identification and detection of drug molecules.It has been preliminarily proved that Fe-CQDs can affect the fluorescence and scattering properties of melatonin,revealing that there is some interaction between Fe-CQDs and melatonin.Combined with the excellent magnetic resonance imaging ability of Fe-CQDs,it is expected to detect melatonin noninvasively and visually in vivo.In addition,it was found that H₂O₂could effectively quench the fluorescence of Fe-CQDs,and the color of Fe-CQDs solution gradually changed from red-brown to colorless,indicating that the structure of Fe-CQDs changed greatly.Similarly,this change may affect the relaxation performance of Fe-CQDs,which has the potential to regulate magnetic resonance signal in the presence of H₂O₂,providing a possibility for noninvasive and quantitative detection of H₂O₂ at the molecular level in vivo.