Preparation And Performances Of Gadolinium(3+)-doped Carbon Quantum Dots As A Magnetic Resonance/Fluorescence Bimodal Contrast Agent

In recent years, the bimodal contrast agent combining of gadolinium ion chelate and semiconductor quantum dots has been developed rapidly. However,the toxicity of semiconductor quantum dots limits the application of this kind of contrast agent, and the construction process of this kind of contrast agent is extremely complex. In this work, We reported a bimodal contrast agent constructed by Gd?3+? ions in combination with carbon quantum dots?CQDs?.At the same time, the relationship between the structure and properties of the magnetic resonance/fluorescence bimodal contrast agent was explored. In addition, the factors affecting the performances of the optical emission were also discussed.1. In order to overcome the defects of the MRI contrast, a magnetic resonance/fluorescence bimodal contrast agent was constructed by combining carbon quantum dots?CQDs? with Gd?3+? ions, taking advantage of the good biocompatibility and excellent photoluminescence properties of carbon quantum dots. In the paper, a kind of CQDs which are doped with Gd?3+? ions was prepared by hydrothermal method under 220? for 8 h and employing gadopentetate monomeglumine?Gd PM? as a precusor. The prepared Gd³⁺-CQDs with the diameter of about 0.5².75 nm show little cell toxicity and exhibit a photoluminescence quantum yield of 7.1 %, as well as a r1 value of 9.87mM-1?S-1?[Gd?3+?]=0.01 mM? with the doping amounts of Gd?3+? ions 16.7wt%. Besides, Gd³⁺-CQDs exhibit photoluminescence properties notably who emit bright blue fluorescence when exposed to 365 nm UV light.2. The structure and properties of the prepared dual modality contrast agent were analyzed systematically by changing the pyrolysis method and employing hydrothermal method to carbonize the precursor. Carbonaceous cores are generated from the carbonization of Gd PM, which are characteristic of amorphous mainly. And there is a well-developed cluster-like structure: each cluster is composed of many primary nanoparticles with a mean size of 0.5².8nm. Meanwhile, the electron diffraction pattern of Gd³⁺-CQDs shows a typical amorphous character. In addition, the experimental results show that in certain range, the increase of the carbonization degree is conducive to the photoluminescence of Gd³⁺-CQDs. Hence, increasing the reaction temperature and prolonging the reaction time have the same effects in getting better photoluminescence of Gd³⁺-CQDs.There are several hydrophilic groups such as hydroxyl?-OH? and carboxylate?-COO-? on the surface of carbonaceous cores. The hydroxyl groups are derived from partly carbonized meglumine unit of Gd PM, and the-COOgroups are introduced by the gadopetic acid unit. It is-OH and-COO- groups endow Gd³⁺-CQDs good hydrophilic ability and surpport coordination site to Gd?3+?. In Gd³⁺-CODs, a few of Gd2O3 at high temperature besides Gd?3+?chelates are doped on the CQDs surface; And the content of gadolinium ions showed a positive relationship with the relaxation rate of the carbon quantum dots.3. To lay the theoretical foundation for further optimizing the photoluminescence properties, we explore the factors that affect the fluorescence of Gd³⁺-CQDs. The results show that the different post processing techniques and in vivo environment have a great influence on the quantum yield of Gd³⁺-CQDs.In the normal human p H range, Gd³⁺-CQDs has a good photoluminescence performance, which shows that Gd³⁺-CQDs is not affected by human p H when used as in vivo contrast agent. Besides, Gd³⁺-CQDs can show excellent luminescence properties in the physiological saline,, but if the concentration of Na Cl is too large, it's the photoluminescence properties will reduce. Furthermore,-C=O in Gd³⁺-CQDs will be reduced to-C-OH by Na BH₄, thereby reducing its photoluminescence ability. Moreover, element doping can also affect the photoluminescence ability of Gd³⁺-CQDs, for example, it can improve the ability of light emission when doped with electron elements?such as nitrogen?.In this paper, the prepared CQDs whose surface is doped with Gd?3+?showed excellent comprehensive performance as a magnetic resonance/fluorescence bimodal contrast agent. And the systematic study of Gd³⁺-CQDs provides a technical and theoretical basis for the study of high performance dual mode contrast agent.