Both the amphiphilic polymer wrapping procedures were a success to a certain
definitely fluorescence being exhibited by both of the pQDs in an aqueous solvent. Both of the pQDs, however, showed a significant decrease in emission intensity (65%) after the transfer to an aqueous solvent. Interestingly, this decrease in emission intensity was identical for both the Pellegrino and the Anderson procedure. This shows that both of the PMA and mod-PAA are viable options for amphiphilic polymer
wrapping in the future. Multiple wrapping procedures were carried out for both polymers to try and refine the method most effectively (Figure 26).
Figure 26: Picture of all the successful wrapping syntheses for both the Pellegrino procedure (left) and the Anderson procedure (right). The PMA-QD solutions were much brighter and were typically less cloudy than the PAA-QD solutions.
The disparity in the brightness of the two solutions can be accounted for by comparing the original QD fluorescence spectrums in CHCl3(Figure 27). From the fluorescence data, it can be seen that the QD#2s had 33% of the peak emission intensity of the QD#1s, which explains why the PMA-QD solutions are much brighter than the PAA-QD solutions.
Figure 27: Comparison of the fluorescence between QD#1 and QD#2. The peak emission intensity of QD#2 is 33% of the peak emission intensity for QD#1. This explains the difference in the brightness of PMA-QDs vs. PAA-QDs after their transfer to H2O.
5
Conclusion
This project detailed the results of two amphiphilic polymer wrapping processes to obtain aqueous soluble quantum dots. The Pellegrino procedure obtained aqueous soluble quantum dots that emit at a center wavelength of 603 nm. During this process the peak fluorescence intensity of the polymer wrapped quantum dots decreased by 65%, which can be attributed to a decrease in quantum dot concentration due to an incomplete transfer to the aqueous solution. Irradiation of polymer wrapped quantum dots in H2O lead to a 1.7x permanent fluorescence enhancement, giving an overall fluorescence decrease after transfer of 40.5%. The Anderson procedure obtained aqueous soluble quantum dots that emit at a center wavelength of 559 nm. During this process the peak fluorescence intensity of the polymer wrapped quantum dots
decreased by 65%, which can be attributed to an increase in scattering by undissolved particulate matter. Irradiation of polymer wrapped quantum dots in H2O lead to a 3.4x permanent fluorescence enhancement, giving an overall fluorescence increase after
transfer of 19%. Both methods of amphiphilic polymer wrapping show promise for obtaining aqueous soluble quantum dots that may be used for biological
References
[1] I.L. Medintz, and H. Mattoussi, “Quantum dot-based resonance energy transfer and its growing application in biology,Phys. Chem. Chem. Phys., 11, (2009): 17–45.
[2] M.A. Hines and P. Guyot-Sionnest, “Synthesis and Characterization of Strongly Luminescing ZnS-Capped CdSe Nanocrystals,J. Phys. Chem., 100, (1996): 468–471.
[3] C.A. Leatherdale, W.-K. Woo, F.V. Mikulec, and M.G. Bawendi, “On the
Absorption Cross Section of CdSe Nanocrystal Quantum Dots,J. Phys. Chem. B, 106, (2002): 7619–7622.
[4] P.M. Allen and M.G. Bawendi, “Ternary I–III–VI Quantum Dots Luminescent in the Red to Near-Infrared,J. Am. Chem. Soc., 130.29, (2008): 9240–9241.
[5] T. Pons, I.L. Medintz, X. Wang, D.S. English, and H. Mattoussi, “Solution-Phase Single Quantum Dot Fluorescence Resonance Energy Transfer,J. Am. Chem. Soc., vol. 128, pp. 15324–15331, 2006.
[6] B.O. Dabbousi, J. Rodriguez-Viejo, F.V. Mikulec, J.R. Heine, H. Mattoussi, R. Ober, K.F. Jensen, and M.G. Bawendi, “(CdSe)ZnS Core–Shell Quantum Dots: Synthesis and Characterization of a Size Series of Highly Luminescent
Nanocrystallites,J. Phys. Chem. B, vol. 101, pp. 9463–9475, 1997.
[7] R.E. Anderson and W.C. Chan, “Systematic Investigation of Preparing Biocompatible, Single, and Small ZnS–Capped CdSe Quantum Dots with Amphiphilic Polyers,ACS Nano, 2.7, (2008): 1341–1352. Print.
[8] T. Pellegrino, L. Manna, S. Kudera, T. Liedl, D. Koktysh, A.L. Rogach, S. Keller, J. Radler, G. Natile, and W.J. Parak, “Hydrophobic Nanocrystals Coated with an Amphiphilic Polymer Shell: A General Route to Water Soluble Nanocrystals,
Nano Letters, 4.4, (2004): 703–707. Print.
[9] D. Battaglia, J. Li, Y. Wang, X. Peng, Colloidal two-dimensional systems: CdSe quantum shells and wells,” Angew. Chem. Int. Ed., 42, (2003): 5035–5039. Print.
[10] P.T. Snee, R.C. Somers, G. Nair, J.P. Zimmer, M.G. Bawendi, and D.G. Nocera, “A Ratiometric CdSe/ZnS Nanocrystal pH Sensor,J. Am. Chem. Soc., 128, (2006): 13320–13321.
[11] S. Sadhu, and A. Patra, “Donor–Acceptor Systems: Energy Transfer from CdS Quantum Dots/Rods to Nile Red Dye,ChemPhysChem, 9, (2008): 2052–2058.
[12] V.I. Klimov, A.A. Mikhailovsky, S. Xu, A. Malko, J.A. Hollingsworth, C.A. Leatherdale, H.J. Eisler, and M.G. Bawendi, “Optical Gain and Stimulated Emission in Nanocrystal Quantum Dots,Science, 290, (2000). Print.
[13] H. Kroemer, “Nobel Lecture: Quasielectric fields and band offsets: teaching electrons new tricks,Reviews of Modern Physics, 23.3, (2001).
[14] R.B. Mujumdar, L.A. Ernst, S.R. Mujumdar, C.J. Lewis, and A.S. Waggoner, “Cyanine Dye Labeling Reagents: Sulfoindocyanine Succinimidyl Esters,
Bioconjugate Chem., 4.2, (1993): 105–111.
[15] W. Yu, L. Qu, W. Guo, and X. Peng, “Experimental Determination of the Extinction Coefficient of CdTe, CdSe, and CdS Nanocrystals,”Chem. Mater., 15, (2003): 2854–2860. Print.
[16] E.M. Boatman, K.J. Nordell, and G.C. Lisensky, “A safer, Easier, Faster Synthesis for CdSe Quantum Dot Nanocrystals,”Journal of Chemical Education, 82.11, (2005):1697–1699.
[17] Z. Zhelev, R. Jose, T. Nagase, H. Ohba, R. Baklova, M. Ishikawa, and Y. Baba, “Enhancement of the photoluminescence of CdSe quantum dots during
long-term UV-irradiation: privelege or fault in life science research?”Journal of Photochemistry and Photobiology B: Biology, 75, (2004): 99–105.
[18] J.R. Lakowicz,Principles of Fluorescence Spectroscopy, Springer, New York, 2006.