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- Carboxylated and Aminated Carbon dots: hydrothermal synthesis, photostability, and DNA interaction studiesPublication . Martins, Ivo José Viveiros; Rodrigues, João Manuel Cunha; Tomás, Helena Maria Pires GasparCarbon dots (CDs) are a class of zero-dimensional nanomaterials that were discovered in 2004. Being composed mainly by carbon, spherical in shape, and with a size ranging between 1-10 nm, hold very interesting properties, such as excellent photostability, low cytotoxicity, surface functionalization and high quantum yields when compared to other fluorophores. Regarding applications, CDs already have a considerable array being used for solar cells, chemical sensing, drug and gene delivery. Specifically, CDs have demonstrated their ability to condense and transfect DNA, as demonstrated by previous works. PAMAM dendrimers are globular molecules that hold very interesting properties for biomedical applications, especially for gene delivery. One of their versatilities is their ability to interact electrostatically with other structures, and results have shown their ability to condense and transfect DNA efficiently. The combination between CDs and PAMAM dendrimers is not broadly considered. Therefore the preparation of a complex between CDs-PAMAM and DNA would be of great interest. The capacity of CDs to act as a fluorescent probe and to condense DNA, combined with PAMAM dendrimers to efficiently guide the complex towards the interior of the cells, could provide an interesting platform for gene delivery applications. Nonetheless, the preparation of this type of complex is highly dependent on the capacity of CDs to maintain its fluorescent properties after complexation with DNA and PAMAM, and so the impact of these interactions on the fluorescence properties should be extensively studied. Here in, we report the synthesis of carboxyl and amine terminated carbon dots, using folic, ascorbic, and oxaloacetic acid as the main starting materials, and the hydrothermal approach as the method of synthesis. Further studies comprising quenching, pH, fluorescence stability over time, and DNA condensation were also performed. The interaction between CDs-DNA and CDs-PAMAM-NH2 was also tested, aiming at studying the impact on the fluorescence properties of the dots. The results obtained, particularly TEM, confirm the success of CDs synthesis, and based on FT-IR and -potential, two different amine-type and one carboxylterminated carbon dots were prepared. The carboxyl-CDs in contrast with the other two are relatively photostable and can transfect DNA almost completely. The results from the CDs-DNA interaction based on fluorescence spectroscopy, confirm the quenching effect by DNA. Lastly, the CDs-PAMAM interaction was tested using carboxyl-terminated carbon dots, and the results obtained also confirm a quenching effect by the G5 PAMAM-NH2 on the fluorescence of CDs, and interestingly G5 PAMAM-NH2 was able to enhance the fluorescence between 400-500 nm excitation when compared to the control.
- Engineered fluorescent carbon dots and G4-G6 PAMAM dendrimer nanohybrids for bioimaging and gene deliveryPublication . Martins, Ivo; Tomás, Helena; Lahoz, Fernando; Rodrigues, JoãoABSTRACT: Carbon dots (CDs) and G4-G6 (polyamidoamine)- PAMAM-NH2 dendrimers were self-assembled to produce CDs@ PAMAM nanohybrids for transfection and bioimaging purposes. CDs were synthesized by the hydrothermal method, using ascorbic acid as a starting precursor and characterized by transmission electron microscopy, UV−Vis, and fluorescence (in solution and solid-state) techniques. CDs were electrostatically combined with PAMAM dendrimers at room temperature, and the UV−Vis, fluorescence, and NMR spectroscopies were used to confirm the self-assembly. When compared to pristine CDs, nanohybrids were more photostable, resisting high acidic and basic pH. Moreover, they were considerably internalized by cells, as assessed by flow cytometry and fluorescence microscopy, and, when excited, displayed multi color emission easily quantified and visualized. These nanoscale hybrids, coined hybridplexes, can condense pDNA and transfecting cells successfully, particularly the G5 CDs@PAMAM nanohybrids. In summary, CDs prepared in mild and smooth lab conditions, showing good optical properties, were used to prepare elegantly CDs@PAMAM nanohybrids with promising biomedical applications.