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URS presentation (final)

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  1. 1. Quenching of [Ru(bpy)3]2+ Emission by Binding to Ag Nanoparticles Sisi Hu, Matthew Feliciano, Alexander Santulli and Jianwei Fan, Department of Chemistry and Biochemistry, Manhattan College, Bronx, NY 10471
  2. 2. Introduction: Tris(2,2-bipyridyl)ruthenium, Ru(bpy)3 2+, has been well studied due to its strong absorption and emission of UV/visible light and its potential use in solar energy conversion. http://omlc.org/spectra/PhotochemCAD/html/085.html
  3. 3. Recent studies (Huang & Murray, Langmuir 2002, 18, 7077-7081) showed that noble metal nanoparticles, e.g., gold-NPs, are potent quenchers of the luminescent excited state of Ru(bpy)3 2+. (Ru(bpy)3 2+)* + Au-NPs (quencher) Ru(bpy)3 2+ + Au-NPs* We are interested in the quenching of the excited state of Ru(bpy)3 2+ by silver nanoparticles with capping agents citrate or polyethylene glycol (PEG). (Ru(bpy)3 2+)* + Ag-NPs (quencher? ) Ru(bpy)3 2+ + Ag-NPs* Sodium Citrate Polyethylene Glycol (PEG) http://www.taringa.net/posts/salud-bienestar/16110303/Toxicos-en-los-cosmeticos.htmlhttp://en.wikipedia.org/wiki/File:Trisodium_citrate.png
  4. 4. 1. Synthesis of Ag-NPs (Jana, N.R.; Gearheart, L. and Murphy, C. J. Chem. Commun., 2001, 617) 10mL of 1mM sodium citrate (or PEG) was added to 10 mL of 0.5mM AgNO3. The mixture solution was then stirred for 30 seconds. 1.2mL of 1mM NaBH4 prepared in de-aired water was added into the solution afterwards. The solution was stirred for another 30 seconds and allowed to sit for 30 minutes for the reaction to occur completely. citrate AgNO3 + NaBH4 ------> Ag-NP(citrate) + 1/2H2 + 1/2B2H6 + NaNO3 The completeness of the reaction was checked by NaCl solution: there is no AgCl ppt after the addition of NaCl to the final solution.
  5. 5. UV/visible characterization of Ag-NP(citrate) in solution: Plasmon resonance: lref. = 390 nm (for average size = 4 nm), lmeas.= 392 nm 392nm
  6. 6. Calculation of the molar concentration of Ag-NP: Assuming the nanoparticle is spherical the volume of the NP is 4/3r3=4/3(2nm)3=33.51nm3 = 3.35x10-20 cm3/NP Using the molar mass of Ag as 107.87g/mol and assuming the density of Ag(s) is 10.49g/cm3, the # of Ag atoms in per nanoparticle is 3.3510-20 cm3/NP 10.49g/cm3 1mol 107.87g 6.02 1023 mol = 1962 atoms/NP The molar concentration of Ag-NP solution 2.3 104MAgNO3 1NP/1962 Ag atoms = 1.20 107M Ag-NP
  7. 7. 2. Determination of molar extinction coefficients of Ag-NPs 0 0.2 0.4 0.6 0.8 1 1.2 1.4 0.00E+00 2.00E-08 4.00E-08 6.00E-08 Absorbance [Ag-NP] (M) Absorbance at 392nm Absorbance at 450nm Absorbance at 286nm Calibration curves for Ag-NP(citrate) (left) and Ag-NP(PEG) (right) at 286, 392 and 450 nm 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 0.00E+00 5.00E-08 1.00E-07 1.50E-07 Absorbance [Ag-NP] (M) Absorbance(286) Absorbance(392) Absorbance(452)
  8. 8. Molar extinction coefficients, e (M1cm1), of Ag-NP and Ru(bpy)3 2+ The result shows that e slightly depends on the capping agents. 286 nm 392 nm 452 nm Ag-NP(citrate) 3.32 0.34 106 2.31 0.02 107 6.54 0.33 106 Ag-NP(PEG) 4.17 0.07 106 1.75 0.18 107 8.95 0.64 106 Ru(bpy)3 2+ 8.70 104 1.26 104
  9. 9. 3. Stern-Volmer Equation: I0/I = 1+ KSV [Q] I0- Emission intensity of Ru(bpy)3 2+in the absence of quencher (Ag-NP) I - Emission intensity Ru(bpy)3 2+in the presence of quencher [Q] - concentration of quencher Ksv - Stern-Volmer constant, measuring quenching efficiency.
  10. 10. Inner filter effect: If the quencher has optical absorption in the excitation region it will decrease the effective intensity of the exciting light available to the fluorophore. As a result, it induces an apparent quenching of emission and increases the real values of the Stern-Volmer quenching constants. Overlay of UV/visible absorption spectra of Ru(bpy)3 2+ (blue) and Ag-NPs (red) 286nm (L L *) 451nm (MLCT)
  11. 11. Measurement of Stern-Volmer constant of Ag-NP(citrate) Method 1: Excitation of Ru(bpy)3 2+ at 286 nm since at which Ag-NP has the least coabsorption. Method 2: Excitation of Ru(bpy)3 2+ at 451 nm but using corrected Stern-Volmer equation for inner filter effect. Method 3: Excitation Ru(bpy)3 2+at 451 nm but adding very low concentration of Ag-NP so that its absorption at 451 nm is negligible (< 2%).
  12. 12. Method 1: Emission Spectra of Ru(bpy)3 2+ in the presence of increasing concentrations of Ag-NP (lex =286 nm) (left) and corresponding Stern-Volmer plot (right) 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 0 1E-08 2E-08 3E-08 4E-08 5E-08 6E-08 I0/I [Ag-NP] M Ksv is 9.46x106 -1 Ru(bpy)32+ 1.20 108 M Ag-NP 2.40 108 M Ag-NP 3.60 108 M Ag-NP 4.80 108 M Ag-NP 6.00 108 M Ag-NP
  13. 13. Method 2: Excitation at 451 nm but using corrected Stern-Volmer equation for inner filter effect. A correction factor is introduced by Borissevitch, Journal of Luminescence, 81 (1999): (I0/Iem ) = 1 + Ksv [Q] = 0(110 ) (110 0) where is the correction factor for the excitation light, 0 is the fluorophore absorbance, and is the total absorbance of the fluorophore and the quencher at the excitation wavelength, respectively.
  14. 14. Emission Spectra of Ru(bpy)3 2+ in the presence of various concentrations of Ag-NP at lex =451 nm (left) Correction factor ( ) and corrected emission intensities (h0/I) vs. concentrations of Ag-NP added (right) # of Ru(bpy)3 2+ solution M of Ag-NP added Abs(451nm) (I0/Iem ) 1 0 0.31277 1 1 2 1.20 108 0.39037 0.926 1.191 3 2.40 108 0.47924 0.850 1.235 4 3.60 108 0.56084 0.788 1.273 5 4.80 108 0.64077 0.733 1.428 6 6.00 108 0.70748 0.692 1.588 Ru(bpy)32+ 1.20 108 M Ag-NP 2.40 108 M Ag-NP 3.60 108 M Ag-NP 4.80 108 M Ag-NP 6.00 108 M Ag-NP
  15. 15. 0 0.5 1 1.5 2 2.5 0 1E-08 2E-08 3E-08 4E-08 5E-08 6E-08 7E-08 I0/I [Ag-NP] Method 2: Stern-Volmer plots of quenching Ru(bpy)3 2+ by Ag-NP (lex = 451 nm) Ksv (corrected) = 9.30 106 1 Ksv (uncorrected) = 2.02 107 1 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 0 1E-08 2E-08 3E-08 4E-08 5E-08 6E-08 7E-08 hI0/I [Ag-NP]
  16. 16. Method 3: Excitation at 451 nm but adding very low concentration of Ag- NP so that its absorption at 451 nm is negligible (< 2%). # of Ru(bpy)3 2+ solution M of Ag- NP added Abs (451nm) Iem I0/Iem 1 0 1.19520 913521 1 2 1.77 109 1.17450 883930 1.026 3 2.35 109 1.17140 872997 1.034 4 2.93 109 1.18030 862964 1.042 5 3.50 109 1.17220 847810 1.055 0.99 1 1.01 1.02 1.03 1.04 1.05 1.06 0 5E-10 1E-09 1.5E-09 2E-09 2.5E-09 3E-09 3.5E-09 4E-09 I0/I [Ag-NP] Ksv = 9.10 106 1
  17. 17. Summary of Stern-Volmer constant Method 1 (ex=286nm) Method 2 (ex=451nm with correction) Method 3 (ex=451nm) Ksv 9.46 106 1 9.30 106 1 9.10 106 1 Average Ksv 9.280.18 106 1
  18. 18. 4. Spectroscopic titration of Ru(bpy)3 2+by Ag-NPs To check any chemical equilibrium between the ground state Ru(bpy)3 2+and Ag- NPs, absorption spectrum of Ru(bpy)3 2+ was monitored after the addition of Ag- NPs as following: 2mL of Ru(bpy)3 2+ solution (c= 8.0x10-5 M) was placed in a cuvet, Ag-NP solution (1.2x10-7 M) was added to the cuvet in 100 mL increment, UV/vis absorption spectrum of Ru(bpy)3 2+ was recorded after each addition until the spectrum shows no further change.
  19. 19. UV/vis spectra of 8.0x10-5 M Ru(bpy)3 2+ after addition of Ag-NP (0-7.2x10-5 M) 540nm [Ag-NP] increases Isosbestic point 340nm
  20. 20. Titration curve: Absorbance (540 nm) vs. volume of Ag-NP added (left) Absorbance (540 nm) vs. [Ag-NP]/[Ru(bpy)3 2+] (right) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0 500 1000 1500 2000 2500 3000 3500 A(540) mL of Ag-NP 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0 0.0005 0.001 0.0015 0.002 0.0025 A(540) [Ag-NP]/[Ru] [Ru]/[Ag-NP] = 500
  21. 21. Discussion: 1. Stern-Volmer constants obtained from three methods are consistent with each other: emission quenching does happen by Ag-NPs. 2. Stern-Volmer constant (9.280.18 106 1) seems too large for dynamic (or collisional) quenching: = t, where t is the lifetime of the excited state of Ru(bpy)3 2+ (610 ns), and is bimolecular quenching rate constant. For dynamic quenching, , is diffusion rate constant, equals to109 in water. However, = / t = 9.28 106 / 610 109 = 1.5 1013 = 109 .
  22. 22. Discussion Contd 3. Our spectroscopic evidence supports a static quenching mechanism which is via the formation of a non-emissive product between the ground state fluorophore and quencher. The new peak at 540 nm indicates the formation of a new product which could be the electrostatic complex between Ru(bpy)3 2+ (positive charged) and Ag-NPs (negative charged due to citrate). The increasing of absorbance at 540 nm is leveling off when the molar ratio is approaching to 500:1 ([Ru]/[Ag-NP]), which could be the stoichiometric ratio in the product. + Ru(bpy)3 2+ RuAg Ag RuRu Ru - - - - -- - - - -- Ru Ru Ru -: citrate Ru: Ru(bpy)3 2+ Ru
  23. 23. Conclusion: Our research results indicate that the quenching of the excited state of Ru(bpy)3 2+ by Ag-NP is not dynamic but static through the formation of the electrostatic complex between Ru(bpy)3 2+ and Ag-NP(citrate). Future work: Calculating the equilibrium constant K of the association reaction of Ru(bpy)3 2+ and Ag-NPs. Measuring Stern-Volmer constant with Ag-NP (PEG) since PEG is a neutral capping agent.
  24. 24. Acknowledgement: Dr. Harry D. Gafney, Queens College of CUNY

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