Anal. Chem. 2008, 80, 815-818
Reaction of Gold Nanoparticles with Tetracyanoquinoidal Molecules. Spectrophotometric Determination of the Au(0) Content of Gold Nanoparticles Gianni Zotti* and Barbara Vercelli
Istituto CNR per l’Energetica e le Interfasi, c.o Stati Uniti 4, 35127 Padova, Italy Anna Berlin
Istituto CNR di Scienze e Tecnologie Molecolari via C.Golgi 19, 20133 Milano, Italy
The interaction of gold nanoparticles (AuNPs) and typical tetracyanoquinoidal compounds such as bis(dicyanomethylene)-bithiophene and tetracyanoquinodimethane (TCNQ) has been investigated. AuNPs in toluene solution reduce the tetracyano compounds to the radical anion, as shown by UV-vis spectroscopy. The reaction, promoted by the bromide anion used as a stabilizer for AuNPs, involves in the case of TCNQ the total amount of Au(0) in the nanoparticles. A spectrophotometric method for the evaluation of the Au(0) content of capped AuNPs in organic solution has been established and successfully applied to the analysis of dodecanethiol-capped AuNPs.
INTRODUCTION Gold nanoparticles (AuNPs) are particularly investigated due to their potential applications in sensors, nanoelectronic devices, biochemical reagents, and catalysts.1 We are interested in their connection through conjugated pathways, such as those provided by oligothiophenes and, in general, conjugated molecules.2 The possible use of such structures in optoelectronic devices (such as solar cells, light emitting diodes, electronic memories, etc.) is being explored intensively.3 In search of novel properties of AuNPs by interaction with organic semiconductors such as bis(dicyanomethylene)-oligothiophenes,4 we have investigated their reciprocal interaction. Here, we report on the reaction of 5,5′-bis(dicyanomethylene)5,5′-dihydro-2,2′-bithiophene (T2CN4) and tetracyanoquin* To whom correspondence should be addressed. Phone: (39) 049-829-5868. Fax: (39) 049-829-5853. E-mail:
[email protected]. (1) Daniel, M. C.; Astruc, D. Chem. Rev. 2004, 104, 293. (2) Zotti, G.; Vercelli, B.; Berlin, A.; Battagliarin, M.; Herna´ndez, V.; Lo´pez Navarrete, J. T. J. Phys. Chem. C 2007, 111, 5886. (3) (a) Huynh, W. U.; Dittmer, J. J.; Alivisatos, A. P. Science 2002, 295, 2425. (b) Dabbousi, B. O.; Bawendi, M. G.; Onitsuka, O.; Rubner, M. F. Appl. Phys. Lett. 1995, 66, 1316. (c) Tseng, R. J.; Huang, J.; Ouyang, J.; Kaner, R. B.; Yang, Y. Nano Lett. 2005, 5, 1077. (d) Franke, M. E.; Koplin, T. J.; Simon, U. Small 2006, 2, 36. (4) Janzen, D. E.; Burand, M. W.; Ewbank, P. C.; Pappenfus, T. M.; Higuchi, H.; da Silva Filho, D. A.; Young, V. G.; Bredas, J. L.; Mann, K. R. J. Am. Chem. Soc. 2004, 126, 15295. 10.1021/ac701715y CCC: $40.75 Published on Web 01/10/2008
© 2008 American Chemical Society
odimethane (TCNQ), illustrated in Chart 1, with tetraoctylammonium bromide-stabilized AuNPs in toluene, which is its most common form in organic medium.5 The investigation, performed with the use of UV-vis spectroscopy and electrochemistry, has shown that TCNQ operates the complete oxidation of the zerovalent gold content of the nanoparticles, thus allowing the establishment of a novel, easy, and fast method for the analysis of gold nanoclusters in organic solvents. EXPERIMENTAL SECTION Chemicals and Reagents. T2CN4 was prepared as reported in the literature.6 TCNQ (98%, from Fluka) was recrystallized from acetonitrile, which was reagent grade (Uvasol, Merck) with a water content of
