1. Singlet Oxygen Generation from Water-soluble Quantum Dot- Organic Dye Nanocomposites Lixin Shi, Ana Gamboa, Billy Hernandez, Araceli B. Dasalla, and Matthias Selke* Department of Chemistry and Biochemistry, California State University, Los Angeles, Los Angeles, CA 90032 Results and discussion In a typical assay, the Uv-vis spectra of QD-TSPP nanocomposites are slightly blue shifted compared with that of free TSPP (Figure 1a), this could be caused by surface plasma change as TSPP deposited on the surface of the QDs, H-aggregates was achieved. 8 An aqueous solution of TSPP with an absorption of 0.10 at 355 nm corresponds to a concentration of 4  10 -2 mM. After TSPP was deposited on the QDs surface, the absorption of nanocomposites at 355 nm was improved significantly to 0.476 corresponding to s a TSPP concentration 2.6  10 -2 mM. Emission intensity of CdTe-TSPP nanocomposites decreased when TSPP deposited on the CdTe surface. The most likely cause is the quenching of photoexcited QDs through charge transfer to the electron-accepting TSPP, which is bound to QDs (Figure 1b). CdTe-TSPP nanocomposites effectively generate 1 O 2 with a quantum yield of 30±9% as shown in Figure 3a. No 1 O 2 was observed when the CdTe nanocrystal was measured in absence of TSPP (Figure 3b). Scheme 1. Fabrication and 1 O 2 generation of CdTe-TSPP nanocomposites References: (1) (a) Alivisatos, A. P. Science 1996, 271, 933. (b) Michalet, X.; Pinaud, F. F.; Bentolila, L. A.; Tsay, J. M.; Doose, S.; Li, J. J.; Sundaresan, G.; Wu, A. M.; Gambhir, S. S.; Weiss, S. Science, 2005, 307, 538. (2) (a) Medintz, I. L.; Clapp, A. R.; Mattoussi, H.; Goldman, E. R.; Fisher, B.; Mauro, J. M. Nat. Mater. 2003, 2, 630. (b) Bakalova, R.; Ohba, H.; Zhelev, Z.; Nagase, T.; Jose, R.; Ishikawa, M.; Baba, Y. Nano Lett. 2001, 4, 1567. (3) (a) Yokoyama, M.; Satoh, A.; Sakurai, A.; Okano, T.; Matsumura, Y.; Kakizoe, T.; Kataoka, K. J. Control. Release 1998, 55, 219. (b) Leroux, J-C.; Allémann, E.; Jaeghere, F. D.; Doelker, E.; Gurny, R. J. of Control. Release, 1996, 39, 339. (4) (a) Imahori, H.; Arimura, M.; Hanada, T.; Nishimura, Y.;Yamazaki, I.; Sakata, Y.; Fukuzumi, S.; J. Am. Chem. Soc. 2001, 123, 335. (b) Roy, I.; Ohulchanskyy, T. Y.; Pudavar, H. E.; Bergey, E. J.; Oseroff, A. R.; Morgan, J.; Dougherty, T. J.; Prasad, P. N. J. Am. Chem. Soc. 2003, 125, 7860. (5) Hone, D. C.; Walker, P. I.; Evans-Growing, R.; FitzGerald, S.; Beeby, A.; Chambrier, I.; Cook, M. J.; Russell, D. A. Langmuir, 2002, 18, 2985. (6) Wang, S. Z.; Gao, R. M.; Zhou, F. M.; Selke, M. J. Mater. Chem. 2004, 14, 487. (7) (a) Pinaud, F.; King, D.; Moore, H. P.; Weiss, S. J. Am. Chem. Soc. 2004, 126, 6115. (b) Medintz, I. L.; Uyeda, H. T.; Goldman, E. R.; Mattoussi, H. Nat. Mater. 2005, 4, 435. (c) Pathak, S.; Choi, S. K.; Arnheim, N.; Thompson, M. E. J. Am. Chem. Soc. 2001, 121, 4103. (8) Luo, Y. H.; Huang, J. G.; Ichinose, I. J. Am. Chem. Soc. 2005, 127, 8296. Introduction Colloidal semiconductor nanocrystals (Quantum Dots, QDs) can provide three-dimensional (3D) architectures and have attracted widespread interest, since their nano-size physical properties are quite different from those of the bulk materials depending upon their size, shape, and packing density. 1 Meanwhile, QDs are very attractive as biology labels, because of their small size, emission tunability, superior photostability and longer photoluminescence decay times. QDs can be used mark moleculer of into living cells. 2 Photodynamic therapy (PDT) is an emerging modality for the treatment of a certain types of cancer. 3 Recent papers have reported high quantum yields of singlet oxygen ( 1 O 2 ) being generated by combining nanoparticles with photosensitizers. 4, 5 Nanoparticles can be ideal carriers of photosensitizer molecules for PDT. The combination of nanomaterials alone with photosensitizers has emerged as a new interdisciplinary research field. 6 However, to the best of our knowledge, no studies on the water-soluble QDs-organic dye nanocomposites for generating singlet oxygen are published to date. Water-soluble species are critical for artificial biocompatibility materials which are widely used as drug delivery carriers, live cell imaging and in vivo imaging. 7 We report herein the first preparation of water-soluble QDs, CdTe, fabricated together with an organic dye, Meso-Tetra (4-sulfonatophenyl) Porphine Dihydrochloride (TSPP), a photosensitizer, using electrostatic interactions as a versatile means to bind photosensitizers to water-soluble CdTe nanocrystals. Future research To investigate the relationship of QD size and quantum yield. To investigate the relationship of space between QD and organic dye on quantum yield. Meso-Tetra (4-sulfonatophenyl) Porphine Dihudrochloride ( TSPP ) CdTe-TSPP nanocomposties after 30 min. irradiation Figure 2. High resolution TEM image of CdTe nanocrystals(10 -3 mM), left, and CdTe-TSPP nanocomposites ( 10 -3 mM CdTe with 10 -3 mM TSPP), right. Scale bar 5 nm. Photooxidation experiments were carried out to determine the stability of the nanocomposites and possible oxidation of the nanocomposites by 1 O 2 using 1 H NMR. Methionione was added into prepared samples of CdTe and CdTe-TSPP, respectively. At high concentration no decomposition or oxidation was detected by 1 H NMR spectroscopy, which further confirms that no singlet oxygen is produced by CdTe nanocrystals. Figure 3. a) Relative intensity of 1 O 2 production vs. absorbance of CdTe-TSPP nanocomposites, TSPP, and Rose Bengal at 355 nm. b). 1 O 2 luminescence decay of CdTe and CdTe-TSPP in presence/absence of Sodium Azide at 355 nm in D 2 O. C). Photooxidation of CdTe-TSPP nanocomposites at different irradiation times. Figure 1. a) Uv-vis spectra for the fabrication of CdTe with TSPP in 0.1 M pH 7.0 PBS. b) Fluorescence spectra of CdTe, TSPP and CdTe-TSPP nanocomposites, respectively. CdTe-TSPP nanocomposites in D 2 O CdTe nanoparticles in D2OCdTe nanoparticles after 30 min irradiation b) c) a)b) Acknowledgment: The authors thank the NSF PREM and NIH MBRS programs for financial support, and Carol M. Garland of CalTech for TEM measurements. a)