Discipline: Nanoscience
Subcategory: Materials Science
Session: 3
Room: Park Tower 8216
Julio A. Rivera de Jesus - University of Puerto Rico- Mayaguez Campus
Co-Author(s): Sonia J. Bailon Ruiz, University of Puerto Rico-Ponce Campus, Ponce, P.R., Oscar J. Perales Perez, University of Puerto Rico-Mayaguez Campus, Mayaguez, P.R.
Semiconductors quantum dot (QDs) are fluorescent nanocrystals with a ranging diameter of 2 nm – 10 nm. Due to their intrinsic optical properties, which are dependent of their size, these nanoparticles have many industrial and bio-medical applications e.g. bio-imaging, diagnostic, LED?s (light emitting diode) production, photocatalyst of organic compounds. More recent applications are based on their potential use as photosensitizer to generate cytotoxic reactive oxygen species (ROS) when activated by light. The factors that govern the cytotoxicity associated to the generation of ROS include the particle size, shape, surface chemistry, the presence of lattice defects, degree of aggregation, among others. Based on these considerations, the present work was focused on: (i) the development of an aqueous synthesis protocol of pure and doped ZnS-based QDs, (ii) the modification of their surface chemistry with biocompatible molecules and, (iii) evaluation of their potential capacity to generate ROS under light irradiation. QDs were synthesized in water using a microwave reactor system under controlled temperature and reaction time in presence of 3-mercaptopropionic acid (MPA) as sulfide supplier. ZnS QDs were also doped with Mn2+ or Cu2+ to a 0.25% Cu:Zn and Mn:Zn molar ratio. As-synthesized ZnS QDs, were characterized by X-ray Diffraction (XRD), HRTEM, UV-Vis and Photo-luminescence spectroscopy techniques. UV-Vis analyzes evidenced the presence of excitonic peaks around 310 nm, 314 nm and 315 nm for ZnS, Cu-ZnS and Mn-ZnS, respectively. The band gap energy of the pure ZnS QDs was estimated at 3.70 eV that indicates a strong quantum confinement effect (3.54 eV for bulk). In addition, the photoluminescence analyses exhibited a strong emission peak (438nm for pure ZnS) that was red-shifted when Mn2+(487nm) or Cu2+ (521nm) were used as dopant species. The incorporation of these transition metals into the ZnS lattice should have created new intermediate energetic levels between the valence and conduction bands of the ZnS particle. The effect of doping on the crystal size and the corresponding capacity of ZnS-based QDs to generate ROS will also be presented and discussed.
Funder Acknowledgement(s): We sincerely acknowledge the CREST initiative for the funding and affiliation to this project. We give our sincere thanks to the Maximizing Access to Research Careers (MARC) for funding this work as a MARC U-STAR trainee.
Faculty Advisor: Oscar J. Perales Perez, julio.rivera23@upr.edu
Role: All experimental procedures and characterization analyses were done by the primary author with exception of HRTEM and XRD measurements.