1. Synthesis and Characterization of Water-Soluble Nanoparticles John R. Renehan, Joseph A. Giesen, April D. Dale, Laura A. Logan, and Deon T. Miles Department of Chemistry Acknowledgments Faculty Research Grants Dr. Dongil Lee, Yonsei University Project Overview Monolayer-protected CdSe and ZnSe quantum dots (qdots) were synthesized in aqueous solutions. Several water-soluble thiols were used to protect the semiconducting core from surface oxidation and to improve the stability of the qdots. Differences in the spectral properties of the qdots were observed as a function of pH. Thiolated crown ether molecules were place-exchanged onto the surface of qdots, and the resulting changes in spectral properties were observed. Separation of the qdots by size was performed using HPLC. From fluorescence spectra of separated qdots, full-width at half-maximum (fwhm) values as small as 14 nm were observed, indicating the isolation of a narrow population size. Water-soluble, monolayer-protected Au 25 nanoparticles were prepared via a place-exchange reaction with organic-soluble nanomaterials and water-soluble thiols. The gold nanomaterial was characterized using electrochemical techniques. Water-Soluble Thiols and Qdot Synthesis 1 We attempted to use HPLC to separate qdots by size. We also hoped to narrow the polydispersity of the qdots. We collected sample fraction from the HPLC at the peaks in the chromatogram and then obtained the fluorescence spectra of those sample fractions. The narrow full-width at half-maximum (fwhm) may correspond to one size of qdot separated from the sample. However, more studies need to be preformed using Transmission Electron Microscopy (TEM) to verify these results. Prof. Miles High Performance Liquid Chromatography of 2.4:1 GLU-CdSe Qdots HPLC Conditions and Parameters Mobile Phase: 50% basic water, 40% methanol, 10% isopropanol Type of Column: Restek® Viva™ C18, 5-μm particles, 300 Å pore diameter Flow Rate =.05 mL/min Quantum Dot Fluorescence Intensity Dependent on Solution pH The intensity of quantum dot fluorescence was measured at various acidities. The study focused on MSA-CdSe qdots and GLU-ZnSe qdots. The effect of the thiol ligands and the quantum dot core were visible. The 50% maximum intensity was used as a significant marker to gauge the qdot character. The influential nature of solution pH provides further insight into the behavior of quantum dots and their fluorescent properties. GLU-ZnSe (1.2:1) Qdots 50% max value = 4.63 MSA-CdSe (1.2:1) Qdots 50% max value = 3.59 50% max value = 8.95 A batch of TGL-CdSe 2.4:1 quantum dots (16 April 2008) were found to have retained fluorescence significantly beyond the expected lifespan. While the basis for this exceptional stability is still under investigation, the qdot size increase continues to be monitored. Qdots were refluxed for 3 hours after Day 279 Jack Joseph April Laura Synthesis of Water-Soluble Au 25 MPCs from Organic-Soluble Nanoparticles Project Goals Synthesize water-soluble Au 25 nanoparticles from organic-soluble nanoparticles Experimental Synthesis of C6 18 Au 25 monolayer protected clusters (MPCs) was carried out according to established method. 3 Water-soluble thiols were used in a place-exchange reaction with C6 18 Au 25 MPCs. Differential Pulse Voltammetry (DPV) was used to characterize isolated MPC products. Electrochemical measurements are useful in exploring the size-dependent electronic charge properties and the electronic structure of small-core MPCs. DPV of 6.4×10 –5 M water-soluble MPC product in 0.1 M NaClO 4 Results C6 18 Au 25 MPCs produced water-soluble nanoparticles through a place-exchange reaction with MSA. C6 18 Au 25 MPCs do not dissolve in 0.1 NaClO 4, ethanol, or methanol. C6 18 Au 25 MPCs did not precipitate and remained in liquid form in a place-exchange reaction with TGA. Future Work Characterize synthesized nanoparticles using UV-Vis spectroscopy Synthesize Au 25 MPC using other water-soluble thiols Project Goals Determine synthetic methods of addition of crown ethers (CEs) with qdots with varying thiol ligands. Ascertain how the coordination of crown ethers around alkali metals affects the fluorescence character of qdots. Effect of Crown Ethers on Fluorescence of Quantum Dots Future Work Determination of varying chain lengths on fluorescence characteristics Use other Na + harvesting molecules Effects of CE and stacking on qdot stability R = x Carbon chain qdot Crown Ether Stacking R = x Carbon Chain length + qdot X= 4 or 12 Side View of Crown Ether Stacking Results EDTA has a high affinity for qdots and produced large non-fluorescent particles that precipitate from solution. Separation of qdot solution from precipitated EDTA, is difficult due to affinity of qdots to glass frit and filter paper. NH 4 OH is the preferred base due to difficult removal of EDTA, and lack of interaction with CE. 2 Preliminary data suggest that restriction due to CE does produce change in MAX. Adjust Cd(ClO 4 ) 2 or Zn(ClO 4 ) 2 solution to basic pH (~11) and deaerate with N 2 Refluxing mixture results in an increase in qdot size Qdot solution is dialyzed using cellulose ester membrane (MWCO: 3,500) H 2 Se H 2 SO 4 N2N2 Al 2 Se 3 Cd(ClO 4 ) 2H 2 O or Zn(ClO 4 ) 26H 2 O H 2 O-soluble thiol Advantages: Simple & high reproducibility Qdots illuminated with Ambient Light Qdots illuminated with UV Light (λ EXC = 365 nm) Change of Quantum Dot Fluorescence over Extended Time Periods Current (A) Au 25 MPC Electrochemistry References 1)Gaponik, N. et al. J. Phys. Chem. B 2002, 106, 7177-7185. 2)Lin, S.-Y. et al. Anal. Chem. 2002, 74, 330-335. 3)Kim, J. et al. Langmuir 2007, 23, 7853-7858. Place Exchange Reaction