Discipline: Chemistry and Chemical Sciences
Subcategory: Chemistry (not Biochemistry)
Julio Rivera - University of Puerto Rico- Mayaguez Campus
Co-Author(s): Sonia J. Bailion Ruiz, University of Puerto Rico, Ponce, PR.
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 like bio-imaging, diagnostic, the production of LED’s (light emitting diode) and Photodynamic Therapy. As results of the extensive number of application of these nanostructures, their potential impact, once released into environment, they are of concern. Surface modification of quantum dots employing bio-compatible compound, like peptides and proteins, could affect their interaction with biological system like aquatic organism. Based on the considerations discussed, the present work is focused on the development of a protocol of ligand-exchange to remove the original cover (thioglycolic acid) from the CdSe(S) quantum dots surface by a new cover (glutathione). Synthesized TGA-capped water-stable nanoparticles were optically characterized by UV-Vis and Pholuminescence spectroscopies. UV-Vis analyzes evidenced the presence of a shoulder peak at 400 nm which suggests the formation of a solid like structure solution containing CdSe or CdS. Subsequently, the band gap energy of these nanomaterials was estimated at 2.32 eV which indicates a strong quantum confinement. In addition, the Photoluminescence spectra of produced nanoparticles showed a high emission peak at 552 nm. After functionalization, the band gap of glutathione capped-quantum dots was around 2.32 eV and a slight blue-shift (545 nm) was observed in photoluminescence measurements because of change in surface states of the QDs. The small size of these nanostructures was verified by HRTEM images and the functionalization by FT-IR spectroscopy. Studies of the toxicity of Cd on a nanoscale size and Cd2+ were also evaluated in an aquatic biological system. Preliminary studies suggested massive deaths at concentrations greater than 100 ppm of cadmium sulfate in Artemia Salina. The toxicity of TGA-capped nanoparticles was evaluated and compared with the toxicity of glutathione capped quantum dots. These results demonstrated that the chemical surface of the nanomaterial is a key factor in their toxicity, less toxicity overall was demonstrated by glutathione capped quantum dots, this could indicate that the molecule, glutathione, is more bio-compatible than TGA. As ongoing remarks, the mechanisms of toxicity of functionalized QDs will be studied in others aquatic organisms and mammalian cells to understand the interaction between nanoparticles and living systems in the environment.
References: Chinnasamy, A., Samou, M., Durai,P. & Devafumar,C. 2014. Toxicity Effect of Silver Nanoparticles in Brine Shrimp Artemia. The Scientific World Journal. Article ID 256919, 10 pages. http://dx.dou.org/10.1155/2014/256919
Bailon, S., Alamo, L. & Perales O. 2012. Synthesis and Surface Functionalization of Water-soluble Quantum Dots. Current Nanoscience. 8:202-207
Funder Acknowledgement(s): Thanks to Dr. Luis Alamo from PUCPR for providing acces to the fluorescence microscope. Lab colleagues, Nadja Maldonado and Jousen Merced for all their help during the project. We also thank UPR-Ponce for providing institutional funding, Instrument Grant by NHI-PRINBRE, and PR-LSAMP.
Faculty Advisor: Sonia J. Bailon Ruiz, firstname.lastname@example.org
Role: Every step of the research was conducted by me, alongside my mentor.