SERS of Semiconducting Nanoparticles (TiO2 Hybrid Composites)

Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439, USA.
Journal of the American Chemical Society (Impact Factor: 12.11). 05/2009; 131(17):6040-1. DOI: 10.1021/ja808277u
Source: PubMed


Raman scattering of molecules adsorbed on the surface of TiO(2) nanoparticles was investigated. We find strong enhancement of Raman scattering in hybrid composites that exhibit charge transfer absorption with TiO(2) nanoparticles. An enhancement factor up to approximately 10(3) was observed in the solutions containing TiO(2) nanoparticles and biomolecules, including the important class of neurotransmitters such as dopamine and dopac (3,4-dihydroxy-phenylacetic acid). Only selected vibrations are enhanced, indicating molecular specificity due to distinct binding and orientation of the biomolecules coupled to the TiO(2) surface. All enhanced modes are associated with the asymmetric vibrations of attached molecules that lower the symmetry of the charge transfer complex. The intensity and the energy of selected vibrations are dependent on the size and shape of nanoparticle support. Moreover, we show that localization of the charge in quantized nanoparticles (2 nm), demonstrated as the blue shift of particle absorption, diminishes SERS enhancement. Importantly, the smallest concentration of adsorbed molecules shows the largest Raman enhancements suggesting the possibility for high sensitivity of this system in the detection of biomolecules that form a charge transfer complex with metal oxide nanoparticles. The wavelength-dependent properties of a hybrid composite suggest a Raman resonant state. Adsorbed molecules that do not show a charge transfer complex show weak enhancements probably due to the dielectric cavity effect.

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    • "In this context, it was recently shown that biologically important molecules exhibit a strong Raman enhancement when they are decorated on TiO 2 nanoparticles [4]. Furthermore, 5 nm TiO 2 nanoparticles covalently tethered to an antibody via a dihydroxybenzene bivalent linker were found to be effective photocatalysts for targeted brain cancer therapy [5]. "
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    • "It suggests that NMR investigation of the protein binding on titania nanoparticles seems unfeasible. Other techniques such as SERS on TiO2 [55] might give additional insight into the attachment mode. "
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    ABSTRACT: Density functional theoretical calculations have been utilized to investigate the interaction of the amino acid arginine with the (100) surface of anatase and the reproduction of experimentally measured 49Ti NMR chemical shifts of anatase. Significant binding of arginine through electrostatic interaction and hydrogen bonds of the arginine guanidinium protons to the TiO2 surface oxygen atoms is observed, allowing attachment of proteins to titania surfaces in the construction of bio-sensitized solar cells. GIAO-B3LYP/6-31G(d) NMR calculation of a three-layer model based on the experimental structure of this TiO2 modification gives an excellent reproduction of the experimental value (-927 ppm) within +/- 7 ppm, however, the change in relative chemical shifts, EFGs and CSA suggest that the effect of the electrostatic arginine binding might be too small for experimental detection. Electronic supplementary material The online version of this article (doi:10.1007/s00894-010-0853-y) contains supplementary material, which is available to authorized users.
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    ABSTRACT: Photo-induced charge transfer process between the carotenoids and (TiO2)15b was theoretically studied with quantum chemical methods, and the charge transfer information of the carotenoid–(TiO2)15 complex were visualized using the charge difference density method. Calculated results show the strongest absorption wavelength is located at 606nm. Electron transfer in the isolated (TiO2)15 was also analyzed in some detail. For 15b (C2v), electrons transfer from one layer to the other layer; while for 15a (C2v), electrons transfer from the outer O atoms to the inter Ti atom.
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