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Probing of Porphyrin Surface Chemistry in Systems with Laser-Ablated Ag Nanoparticle Hydrosol: Role of Thiosulfate Anions Marek Procha´zka,*,†,‡ Blanka Vlcˇkova´,§ Josef Sˇ teˇpa´nek,‡ and Pierre-Yves Turpin† L. P. B. C. (CNRS UMR 7033), Universite´ Pierre et Marie Curie, 4 Place Jussieu, Case 138, F-75252 Paris Cedex 05, France, Institute of Physics, Charles University, Ke Karlovu 5, CZ-12116 Prague 2, Czech Republic, and Department of Physical and Macromolecular Chemistry, Charles University, Hlavova 2030, CZ-12840 Prague 2, Czech Republic Received November 3, 2004. In Final Form: January 27, 2005 The influence of sodium thiosulfate (THS) concentration in Ag colloid/THS/H2TMPyP and Ag colloid/ H2TMPyP/THS systems (H2TMPyP ) 5,10,15,20-tetrakis(1-methyl-4-pyridyl)porphyrin) was investigated by a combination of surface-enhanced resonance Raman scattering (SERRS) spectroscopy, surface plasmon extinction (SPE) measurements, and transmission electron microscopy (TEM). THS was found to have a strong impact on Ag nanoparticle surface structure and aggregation state and on interaction with H2TMPyP probe molecules, as evidenced by variations of the SERRS spectrum. In the Ag colloid/THS/H2TMPyP system, when laser-ablated Ag colloid was THS pretreated prior to the porphyrin addition, a critical threshold THS concentration (4 × 10-5 M) was discovered. At concentrations below the threshold, THS mainly reduces the number of Ag+ adsorption sites. This leads to increased Ag nanoparticle aggregation prior to the porphyrin addition and significant weakening of the overall SERRS signal. Dominant contributions in the SERRS spectrum correspond to free base H2TMPyP and Ag+ containing the AgTMPyP form. At concentrations above the threshold, THS mediates also the formation and stabilization of new adsorption sites, probably Ag(0) sites. This induces a turn in the aggregation state of the pretreated Ag-c/THS system, an increase of the overall SERRS signal, and the appearance of a new spectral form of Ag metalated porphyrin.
Introduction Porphyrins and metalloporphyrins currently attract a specific interest owing to their potential applications in life sciences, including photodynamic therapy (PDT) of cancer,1 antiviral treatments,2 molecular biology,3 specific sensing of DNA sequences, and selective cleavage of nucleic acids.4 Surface-enhanced resonance Raman scattering (SERRS), in which one can benefit from both the molecular resonance effect and the surface enhancement of the Raman scattering of porphyrin molecules adsorbed on a SERRS-active metal surface, is a promising spectroscopic approach for studying porphyrins and metalloporphyrins at extremely low concentrations, close to those encountered under physiological conditions. In porphyrin SERRS-active systems, a metalation process (i.e., incorporation of a metal ion from the metal surface into the porphyrin core) can be detected by monitoring SERRS spectra, as a consequence of direct adsorption of the original free base porphyrin onto the metal surface, for example, Ag substrate. This was first observed at the beginning of the 1980s5-7 and reported for various porphyrins in SERRS-active systems including * To whom correspondence should be addressed. E-mail:
[email protected]. † Universite ´ Pierre et Marie Curie. ‡ Institute of Physics, Charles University. § Department of Physical and Macromolecular Chemistry, Charles University. (1) Dougherty, T. J.; Gomer, C. J.; Henderson, B. W.; Jori, G.; Kessel, D.; Korbelik, M.; Moan, J.; Peng, Q. J. Natl. Cancer I. 1998, 90, 889. (2) Asanaka, M.; Kurimura, T.; Toya, H.; Ogaki, J.; Kato, Y. AIDS (London) 1989, 3, 403. (3) Dabrowiak, J. C.; Ward, B.; Goodisman, J. Biochemistry 1989, 28, 3313. (4) Arthanari, H.; Basu, S.; Kawano, T. L.; Bolton, P. H. Nucleic Acids Res. 1998, 26, 3724.
layered structures,8 roughened electrodes,9 metal liquidlike films (MELLFs),10 and colloids.11-17 Since then, significant progress in porphyrin metalation studies has been achieved by the introduction of a quantitative approach based on factor analysis (FA) methods.18 SERRS spectral changes caused by metalation of the model molecule 5,10,15,20-tetrakis(1-methyl-4-pyridyl)porphyrin (H2TMPyP) adsorbed on Ag colloid (Ag-c) were monitored and treated by FA, which allowed the SERRS spectra of two pure porphyrin species (i.e., free base and metalated) to be characterized and metalation kinetics to be determined in terms of the time dependence of the relative contributions of both species to the original (5) Cotton, T. M.; Schultz, S. G.; Van Duyne, R. P. J. Am. Chem. Soc. 1982, 104, 6528. (6) Itabashi, M.; Kato, K.; Itoh, K. Chem. Phys. Lett. 1983, 97, 528. (7) Shoji, K.; Kobayashi, Y.; Itoh, K. Chem. Phys. Lett. 1983, 102, 179. (8) Kobayashi, Y.; Itoh, K. J. Phys. Chem. 1985, 89, 5174. (9) (a) Qu, J.; Arnold, D. P.; Fredericks P. M. J. Raman Spectrosc. 2000, 31, 469. (b) Qu, J.; Fredericks P. M. Spectrochim. Acta, Part A 2000, 56, 1637. (10) Al-Obaidi, A. H. R.; Rigby, S. J.; Bell, S. E. J.; McGarvey, J. J. J. Phys. Chem. 1992, 96, 10960. (11) Kim, M.; Tsujimo, T.; Itoh, K. Chem. Phys. Lett. 1986, 125, 364. (12) Itoh, K.; Sugii, T.; Kim M. J. Phys. Chem. 1988, 92, 1568. (13) Mou, Ch.; Chen, D.; Wang, X.; Zhang, B.; He, T.; Xin, H.; Liu, F. Chem. Phys. Lett. 1991, 179, 237. (14) (a) Mateˇjka, P.; Vlcˇkova´, B.; Vohlı´dal, J.; Pancˇosˇka, P.; Baumruk, V. J. Phys. Chem. 1992, 96, 1361. (b) Vlcˇkova´, B.; Mateˇjka, P.; Sˇ imonova´, J.; C ˇ erma´kova´, K.; Pancˇosˇka, P.; Baumruk, V. J. Phys. Chem. 1993, 97, 9719. (15) Woolley, P. S.; Keely, J. B.; Hester R. E. Chem. Phys. Lett. 1996, 258, 501. (16) Sˇ mejkal, P.; Vlcˇkova´, B.; Procha´zka, M.; Mojzesˇ, P.; Pfleger, J. Vib. Spectrosc. 1999, 19, 243; J. Mol. Struct. 1999, 482-483, 225. (17) Chowdhury, J.; Ghosh, M.; Pal, P.; Misra, T. N. J. Colloid Interface Sci. 2003, 263, 318. (18) Malinowski, E. R. Factor Analysis in Chemistry, Wiley: New York, 1991.
10.1021/la047307m CCC: $30.25 © 2005 American Chemical Society Published on Web 03/02/2005
Influence of THS Anions on Ag Nanoparticle Hydrosols
experimental spectra.19 The kinetics of metalation was found to be an important probe of Ag-c/porphyrin SERRS systems. For example, a detailed study of the influence of Ag-c surface characteristics and of the porphyrin concentration on the kinetics of metalation was reported.20 Moreover, metalation kinetics was used to probe the surface properties of Ag-c,21 porphyrin self-aggregation,22 and porphyrin interactions with large biomolecules of interest such as nucleic acids.23 For a quantitative analysis of H2TMPyP SERRS spectra, characteristic Raman marker bands of metalated and free base porphyrin forms (mainly at approximately 395, 1340, and 1545 cm-1 and 331, 1337 + 1360, and 1550 cm-1, respectively) were employed. In addition to those, spectral features at approximately 385, 1365, and 1565 cm-1 were, in some cases, encountered in SERRS spectra measured at low porphyrin concentration in laser-ablated Ag-c systems.20,24 The appearance of these bands observed at acidic pH was also reported by Kim et al.11 Similar bands were detected in SERRS spectra of H2TMPyP adsorbed on laser-ablated Ag-c modified by mercaptoacetic acid. This observation was rather surprising, since mercaptoacetic acid, along with other mercaptocarboxylic acids, was expected to behave as a molecular spacer, that is, to prevent free base porphyrin from metalation.16 Although several authors reported the observation of these particular spectral features, experimental conditions necessary for their appearance in SERRS spectra as well as their origin remained to be established. Our preliminary experiments25 have shown that the appearance of these additional features in SERRS spectra of 1 µM H2TMPyP can be induced by the presence of sodium thiosulfate in the systems. In the present paper, we focus on investigations of the role of thiosulfate (THS) ions on laser-ablated Ag-c/H2TMPyP systems. In our experiments, we used a concentration of ∼0.1 µM H2TMPyP, since it corresponds to a sub-monolayer coverage of Ag nanoparticles by porphyrin molecules:26 we thus eliminate a possible interference of H2TMPyP molecules adsorbed in a second layer. The spectrum of a new H2TMPyP form generated in the presence of sodium thiosulfate is reported, that differs from those of H2TMPyP and AgTMPyP species.8,19b,27 In agreement with the previously reported ability of THS ions to remove cationic silver from a Ag surface,28-32 we tentatively assign this new spectral form to H2TMPyP adsorbed on a neutral silver surface. Finally, (19) (a) Procha´zka, M.; Hanzlı´kova´, J.; Sˇ teˇpa´nek, J.; Baumruk, V. J. Mol. Struct. 1997, 410-411, 77. (b) Hanzlı´kova´, J.; Procha´zka, M.; Sˇ teˇpa´nek, J.; Baumruk, V.; Bok, J.; Anzenbacher, P., Jr. J. Raman Spectrosc. 1998, 29, 575. (20) Procha´zka, M.; Sˇ teˇpa´nek, J.; Turpin, P.-Y.; Bok, J. J. Phys. Chem. B 2002, 106, 1543. (21) Procha´zka, M.; Mojzesˇ, P.; Sˇ teˇpa´nek, J.; Vlcˇkova´, B.; Turpin, P.-Y. Anal. Chem. 1997, 69, 5103. (22) (a) Procha´zka, M.; Sˇ teˇpa´nek, J.; Hanzlı´kova´, J.; Mojzesˇ, P.; Baumruk, V.; Anzenbacher, P., Jr. In Spectroscopy of Biological Molecules; Merlin, J. C., et al., Eds.; Kluwer Academic Publishers: Dordrecht, The Netherlands, 1995; p 227. (b) Procha´zka, M.; Sˇ teˇpa´nek, J.; Turpin, P.-Y.; Bok, J. In Proceedings of International Symposium on Progress in Surface Raman Spectroscopy-Theory, Techniques and Applications; Tian, Z. Q., Ren, B., Eds.; Xiamen University Press: Xiamen, China, 2000; p 179. (23) Procha´zka, M.; Sˇ teˇpa´nek, J.; Turpin, P.-Y.; Bok J. J. Mol. Struct. 1999, 482-483, 219. (24) Procha´zka, M.; Sˇ teˇpa´nek, J.; Turpin, P.-Y.; Bok, J. Vib. Spectrosc. 1999, 19, 233. (25) Procha´zka, M.; Turpin, P.-Y.; Sˇ teˇpa´nek, J.; Vlcˇkova´, B. J. Raman Spectrosc. 2002, 33, 758. (26) Procha´zka, M.; Mojzesˇ, P.; Vlcˇkova´, B.; Turpin, P.-Y. J. Phys. Chem. B 1997, 101, 3161. (27) Blom, N.; Odo, K.; Nakamoto, D.; Strommen, D. J. Phys. Chem. 1986, 90, 2847. (28) Watanabe, T.; Kawanami, O.; Honda, K.; Pettinger, B. Chem. Phys. Lett. 1983, 102, 565.
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Figure 1. SERRS spectra of (A) the Ag-c/H2TMPyP system and (B) the Ag-c/H2TMPyP/THS (1 mM) system. Time between the addition of thiosulfate and spectral acquisition (from top to bottom): 1, 5, 15, 20, 30, 50, 60, and 90 min. (C) SERRS spectra of the Ag-c/THS (0.2 mM)/H2TMPyP system. Time between system preparation and spectral acquisition (from top to bottom): 2, 4, 6, 8, and 15 min, 3 h, and 1 day.
we monitor the influence of thiosulfate concentration on the SERRS spectra of adsorbed H2TMPyP, on the surface enhancement, and on the morphology and surface plasmon extinction (SPE) of Ag nanoparticles. Experimental Section Chemicals. Analytical grade chemicals and redistilled deionized water were used for all sample preparations. 5,10,15,20Tetrakis(1-methyl-4-pyridyl)porphyrin (tetra-p-tosylate) (H2TMPyP), sodium thiosulfate (Na2S203, minimum 99% ) THS), and silver foil (99.99%, ∼1 mm thickness) were purchased from Sigma-Aldrich. Preparation of Ag Colloids. Ag-c was prepared by laser ablation according to a previously published procedure.21 Briefly, a silver foil precleaned in 30% HNO3 was immersed in a quartz cell filled with redistilled deionized water (∼20 mL) and irradiated by a focused (5 cm focal length) beam of the 1064 nm line of a Nd:YAG pulsed laser (Quantel YG58110, 10 Hz repetition time, 20 ns laser pulse duration, energy 30 mJ/pulse) for ∼45 min. The solution was continuously stirred by a magnetic bar, allowing secondary fragmentation of primary ablated Ag nanoparticles to be achieved, thus lowering the nanoparticle hydrosol polydispersity.21 The resulting yellow colloid shows a SPE maximum at ∼400 nm and an absorbance maximum (for a 0.2 cm optical length) of ∼0.65 (see Figure 4, curve a). A transmission electron microscopy (TEM) image of a deposited sample of pure Ag-c is shown in Figure 5A. Preparation of SERRS-Active Systems. Ag-c/H2TMPyP systems were prepared by the addition of H2TMPyP stock solution (29) (a) Jian, W.; Dawei, L.; Houwen, X.; Xu, S.; Fan-Chen, L. Spectrochim. Acta 1987, 43A, 375. (b) Dawei, L.; Jian, W.; Houwen, X.; Xu, S.; Fan-Chen, L. Spectrochim. Acta 1987, 43A, 379. (30) Wang, X.; Wen, H.; He, T.; Zuo, J.; Xu, C.; Liu, F. C. Spectrochim. Acta, Part A 1997, 53, 2495. (31) Li, Y.-S.; Cheng, J.; Coons, L. B. Spectrochim. Acta, Part A 1999, 55, 1197. (32) Doering, W. E.; Nie, S. J. Phys. Chem. B 2002, 106, 311.
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Figure 2. SERRS spectra of the three different spectral forms of H2TMPyP surface species. to Ag-c. Ag-c/H2TMPyP/THS systems have been prepared by the progressive addition of appropriate amounts of THS into Ag-c/ H2TMPyP, in which H2TMPyP is fully metalated (as proved by its SERRS spectrum). The final concentration of THS in the systems ranged from 3 × 10-5 to 2 × 10-3 M. On the other hand, Ag-c/THS/H2TMPyP systems have been prepared by the addition of THS to the ablated Ag-c, followed, after 1 min, by stirring and by the addition of H2TMPyP. The final THS concentration in the systems ranged from 1 × 10-8 to 4 × 10-3 M. The H2TMPyP concentration in all systems was 0.1 µM. Instrumentation. SERRS spectra were recorded at room temperature with a Jobin-Yvon T64000 CCD Raman spectrometer by using the 441.6 nm excitation line of a He-Cd laser (Liconix 4050, power 3-4 mW at the sample) and a 60 s accumulation time. The spectral slit width was ∼5 cm-1, and the band position accuracy was
