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Multicolor Dye-Doped Silica Nanoparticles Independent of FRET Jianquan Xu, Jinglun Liang, Jun Li, and Wensheng Yang* State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130012, People’s Republic of China Received July 18, 2010. Revised Manuscript Received August 23, 2010 Multicolor particles were prepared by incorporating two dyes, one fluorescent (fluorescein isothiocyanate) and one phosphorescent (tris(1,10-phenanathroline) ruthenium ion), into the silica matrix. Colors of the particles can be easily tuned by either varying the doping ratios of the two dyes or changing the excitation wavelength while fixing the ratios. The multicolor character of the particles is less sensitive to the location of the two dyes in the silica, since the luminescence of the particles is independent of F€orster resonance energy transfer (FRET).
Introduction During the past decade, extensive attention has been paid to dye-doped luminescent silica particles due to their application potential in biolabeling.1-6 Multicolor dye-doped luminescent silica particles which can be excited by a single wavelength are more attractive, since they can follow more than one biological event simultaneously. A conventional strategy to develop the multicolor silica particles which can be excited by a single wavelength is to combine two or more dyes which can undergo F€orster resonance energy transfer (FRET) into one silica particle. Under illumination, one dye which is excited acts as donor to transfer energy for subsequent excitation of other dye (acceptor). Multicolor luminescent silica particles were acquirable by changing the ratio and thus the FRET efficiency between the donor and acceptor.7-11 It is known that the efficiency of FRET is related to the dipole-dipole coupling between the donor and acceptor. As a result, to fabricate multicolor silica particles based on FRET, it is vitally important to have control over the location and distance between the dyes in each silica particle.12,13 In this work, we report on the fabrication of multicolor silica particles from two dyes, one fluorescent (fluorescein isothiocyanate, FITC) and one phosphorescent (tris(1,10-phenanathroline) ruthenium ion, Ru(phen)32þ). FITC and Ru(phen)32þ showed emission maxima at 525 and 585 nm, respectively, in solution. However, the two dyes had large overlapping regions in their absorption spectra around 450 nm (see Figure S1 in the *To whom correspondence should be addressed. E-mail: wsyang@ jlu.edu.cn. Telephone: þ86-431-85168185. Fax: þ86-431-85168086.
(1) Verhaegh, N. A. M.; Van Blaaderen, A. Langmuir 1994, 10, 1427. (2) Van Blaaderen, A.; Imhof, A.; Hage, W.; Vrij, A. Langmuir 1992, 8, 1514. (3) St€ober, W.; Fink, A.; Bohn, E. J. Colloid Interface Sci. 1968, 26, 62. (4) Rossi, L. M.; Shi, L. F.; Quina, F. H.; Rosenzweig, Z. Langmuir 2005, 21, 4277. (5) Yao, G.; Wang, L.; Wu, Y. R.; Smith, J.; Xu, J. S.; Zhao, W. J.; Lee, E. J.; Tan, W. H. Anal. Bioanal. Chem. 2006, 385, 518. (6) Latterini., L.; Amelia., M. Langmuir 2009, 25, 4767. (7) Wang, L.; Tan, W. H. Nano Lett. 2006, 6, 84. (8) Wang, L.; Zhao, W. J.; Tan, W. H. Bioconjugate Chem. 2007, 18, 297. (9) Li, X. P.; Qian, Y.; Wang, S. Q.; Li, S. Y.; Yang, G. Q. J. Phys. Chem. C 2009, 113, 3862. (10) Chen, C. H.; Liu, K. Y.; Sudhakar, S.; Lim, T. S.; Fann, W.; Hsu, C. P.; Luh, T. Y. J. Phys. Chem. B 2005, 109, 17887. (11) Peng, A. D.; Xiao, D. B.; Ma, Y.; Yang, W. S.; Yao, J. N. Adv. Mater. 2005, 17, 2070. (12) F€orster, Th. In Modern Quantum Chemistry; Istanbul Lectures, Part III; Sinanoslu, O., Ed.; Academic: New York, 1965; p 93. (13) Lakowicz, J. R. Principles of fluorescence spectroscopy, 3rd.; Kluwer Academic: New York, 2006.
15722 DOI: 10.1021/la1028492
Supporting Information). Their common absorbance features and different emission colors made it possible to fabricate multicolor silica particles which can be excited by a single excitation wavelength. The multicolor character of such silica particles is attributed to the superposition of the two dyes’ emissions based on the trichromatic theory of color vision.14,15 It is expected that the color of the silica particles is insensitive to the location and distance between the two dyes, since they could be excited by light with the same wavelength and there is no effective overlapping between the emission of FITC and absorption of Ru(phen)32þ.
Result and Discussion To illustrate the effect of the distribution and distance between the two dyes on emission properties of the resulting silica particles, the two dyes were incorporated into the silica particles by two different methodologies, stepwise-doping and codoping. The two dyes were separated by a 12 nm silica layer in the stepwise-doping and incorporated into the same silica layer in the codoping (see Figure S2 in the Supporting Information). The amount of FITC used was fixed to be 0.06 mg in all the particles, and that of Ru(phen)32þ was increased from 0 to 0.15 mg to fabricate the silica particles. Sizes of all the silica particles were kept to 75 nm to diminish the effect of light scattering on absorption and emission spectra of the particles (see Figure S3 in the Supporting Information). Figure 1A shows the emission spectra of the silica particles prepared by the stepwise-doping method. It is obvious that the silica particles with different amounts of Ru(phen)32þ showed tunable emission which can be readily distinguished by naked eye under a 365 nm UV lamp (Figure 1B). The three kinds of particles in the mixture with green, yellow, and red colors could also be well resolved from one another by fluorescence microscopy (Figure 1C), suggesting the particles were qualified as multicolor markers for biolabeling. With the increased amount of Ru(phen)32þ, the emission of FITC at 525 nm decreased and that of Ru(phen)32þ around 575 nm emerged and became dominant gradually. The emission maximum of Ru(phen)32þ underwent a blue shift (575 nm) compared to that in ethanol solution (585 nm) after being incorporated into the silica particles, attributed to the matrix effect of silica which prevented the impact (14) Balaraman, S. Psychol. Bull. 1962, 59, 434. (15) Wright, W. D. Doc. Ophthalmol. 1949, 3, 10.
Published on Web 09/15/2010
Langmuir 2010, 26(20), 15722–15725
Xu et al.
Letter
Figure 1. (A) Emission spectra of the stepwise-doping silica particles. The excitation wavelength was at 450 nm. (B) Photo of the dispersions of the silica particles under 365 nm UV lamp. The doping amount of FITC was 0.06 mg and those of Ru(phen)32þ were 0, 0.01, 0.02, 0.04, 0.06, 0.10, and 0.15 mg, respectively (from left to right). (C) Fluorescence image of a mixture of three kinds of the particles with green, yellow, and red colors in which the contents of Ru(phen)32þ were 0, 0.04, and 0.15 mg, respectively. The excitation wavelength was at 450 nm, and the magnification was 400.
Figure 2. Variations in ratios of the relative emission intensity of FITC and Ru(phen)32þ in the stepwise- and codoping silica particles with the contents of Ru(phen)32þ.
of the external environment.16-23 It is noted that the emission intensity of FITC at 525 nm decreased with increased amount of Ru(phen)32þ incorporated although the amount of FITC was the same in all the particles. It is likely that the decrease in emission (16) Burns, A.; Ow, H.; Wiesner, U. Chem. Soc. Rev. 2006, 35, 1028. (17) Wang, L.; Wang, K. M.; Santra, S.; Zhao, X. J.; Hilliard, L. R.; Smith, J. E.; Wu, J. R.; Tan, W. H. Anal. Chem. 2006, 78, 646. (18) Juris, A.; Balzani, V.; Barigelletti, F.; Campagna, S.; Belser, P.; Von Zelewsky, A. Coord. Chem. Rev. 1988, 84, 85. (19) Wheeler, J.; Thomas, J. K. J. Phys. Chem. 1982, 86, 4540. (20) Innocenzi, P.; Kozuka, H.; Yoko, T. J. Phys. Chem. B 1997, 101, 2285. (21) Ogawa, M.; Nakamura, T.; Mori, J.; Kuroda, K. J. Phys. Chem. B 2000, 104, 8554. (22) Rampazzo, E.; Bonacchi, S.; Montalti, M.; Prodi, L.; Zaccheroni, N. J. Am. Chem. Soc. 2007, 129, 14251. (23) Zhang, D. W.; Wu, Z. Z.; Xu, J. Q.; Liang, J. L.; Li, J.; Yang, W. S. Langmuir 2010, 26, 6657.
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intensity of FITC with increased amount of Ru(phen)32þ should not be attributed to FRET since the distance between the two dyes was 12 nm, larger than that for effective FRET (
