Subcategory: Cancer Research
Eric R. Calderon-Ortiz - UPR-Medical Sciences Campus
Co-Author(s): S. Bailón-Ruiz, University of Puerto Rico at Ponce, Ponce, PR Rodriguez-Orengo, University of Puerto Rico - Medical Sciences Campus, San Juan, PR Perales-Perez, University of Puerto Rico at Mayagüez, Mayaguez, PR
Nanomedicine can be described as the process of diagnosing, treating, and preventing disease using nanostructured materials with specific properties to improve human health. Quantum dots (QDs) hosts suitable optical properties for light-driven therapies, e.g. Photo-dynamic Therapy (PDT), for Cancer treatment. The efficacy of QDs-assisted PDT relies on the capacity of QDs to generate reactive oxygen species (ROS), a capability that can be enhanced by inducing structural defects in the nanomaterial lattice. Although the generation of defects in QDs, and the corresponding modifications in their optical properties, could be commonly enhanced by doping and changing the crystal size, there is a lack of systematic research on the influence of the surface chemistry on the promotion of those defects that would promote the generation of ROS. On this basis, the present research is focused on the synthesis of water-stable ZnSe(S) QDs via a Microwave-Assisted synthesis approach in presence of different thiols like L-Cysteine, 3-mercaptopropionic acid (MPA) and 6-mercaptohexanoic acid (MHA). The thiols would act as the source of sulfide species during the QDs synthesis as well as surface functionalization agents of the solids produced. The generation of defects and the tunability of the corresponding optical properties were achieved by a suitable control of the reaction temperature (80°C- 180°C, reaction time (10 minutes – 60 minutes) and a suitable pH value. The photoluminescence of MPA-capped ZnSe(S) showed a band gap peak at 363 nm and a trap emission peak at 450nm, the later attributed to structural defects. The ratio between the two PL peaks (band gap emission peak/trap emission peak) was 2.8 for MPA-capped ZnSe (S) QDs. In the case of L-Cysteine capped ZnSe (S) only the band gap emission peak at 376 nm was observed whereas the MHA-capped ZnSe(S) QDs showed a band gap emission peak and a trap emission peak centered on 390nm and 471nm, respectively, for an intensity ratio (band gap emission/trap emission) of 0.8. These results evidenced that MHA caused the enhancement of the trap emission peak intensity. Consequently, these MHA-capped ZnSe(S) QDs should be excellent candidates to give a high yield of ROS. The difference in the surface chemistry was corroborated by FT-IR measurements. For similar synthesis conditions, the emission peaks exhibited a red-shift that was more pronounced when the QDs were produced in MHA. The mechanisms involved with the observed features in the photoluminescence of the QDs and their corresponding band gap energies will be detailed and discussed.
Funder Acknowledgement(s): This research is supported by NSF-Grant No. HRD 1345156 (CREST II program).
Faculty Advisor: Oscar Perales, email@example.com
Role: All of the research was done by Eric Calderon in Dr. Perales research group.