Banca de DEFESA: IVY SANTOS SOARES

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : IVY SANTOS SOARES
DATE: 30/10/2025
TIME: 09:00
LOCAL: Google Meet
TITLE:

Carbon dots derived from biomass, citric acid, and nitrogen-containing molecules: An in vitro study of antioxidant, pro-oxidant, photoprotective, and antibacterial properties.

KEY WORDS:

Nitrogen-doped carbon dots; pro-oxidant and antioxidant capacity; fibroblast migration; photoprotection.

PAGES: 122
BIG AREA: Ciências Exatas e da Terra
AREA: Química
SUMMARY:

The use of carbon dots (CDs) in biomedicine has been expanding due to their luminescent properties, low toxicity, biocompatibility, photostability, functional versatility, and low cost. In this thesis, multifunctional CDs were synthesized and characterized from sustainable precursors (citric acid, urea, neutral red, ophenylenediamine, and toilet paper roll) using microwave-assisted and hydrothermal methods. The obtained nanomaterials (CD-P, CD-ACU, CD-OPD, CD-MCA20, and CD-ACNR) exhibited sizes below 10 nm, functional groups consistent with the precursors, excellent photostability, and UV-Vis/FTIR spectra with ππ* and n-π* transitions and characteristic oxygen- and nitrogen-containing vibrations. The optical properties revealed tunable emissions, with CD-ACNR displaying dual emission (dependent at 475 nm and independent at 602 nm). CD-ACU and CD-MCA20 showed blue emissions at 537 nm (λexc = 480 nm) and 473 nm (λexc = 380 nm), respectively, while CD-OPD presented a maximum emission at 550 nm (λexc = 450 nm). Flexible and transparent fluorescent films were also produced, maintaining emission behavior similar to aqueous suspensions. Antioxidant assays (ABTS, DPPH, FRAP) demonstrated the CDs’ ability to scavenge ROS. CDACU showed the best performance against HOCl (IC₅₀ = 18.6 ± 3.2 µg·mL⁻¹). In the superoxide assay, CDOPD and CD-ACU were inactive, whereas the others displayed antioxidant activity. Given their dual pro- and antioxidant features, the CDs were evaluated as photosensitizers in singlet oxygen assays. CD-ACU achieved a yield of 13.7 in DPBF degradation (λ_exc = 650 nm, 50 mW, 10 min), a significant result compared to literature and to methylene blue, the reference photosensitizer. Photoprotective activity was investigated in Lanette formulations, with SPF values of CD-ACU (7.3–11.4), CD-MCA20 (14–18.3), and CD-NR (3.7–4.3). Only CD-ACNR did not reach the minimum SPF required by ANVISA (≥6). In antibacterial assays, CDACNR showed complete inhibition of Staphylococcus aureus and Pseudomonas aeruginosa, evidencing strong antimicrobial activity. Moreover, the CDs exhibited low toxicity, good biocompatibility in HaCaT cells (MTT), and enhanced fibroblast migration, reinforcing their potential for biomedical applications.

COMMITTEE MEMBERS:
Interno(a) - 1121343 - ANA MARIA QUEIJEIRO LOPEZ
Presidente - 1869296 - CINTYA D'ANGELES DO ESPIRITO SANTO BARBOSA
Interno(a) - 2089941 - DIMAS JOSE DA PAZ LIMA
Externo(a) à Instituição - GEORGE RICARDO SANTANA ANDRADE - UFES
Interno(a) - 1006306 - JADRIANE DE ALMEIDA XAVIER
Externo(a) à Instituição - SENDY MELISSA SANTOS DO NASCIMENTO - UFRN