Assembling Covalently Linked Nanocrystals and Nanotubes through Click

In this Letter, we describe the important initial results obtained by using the Husigen cycloadditon reaction in the case of gold nanorods and CdSe nanocrystals to produce covalently linked assemblies. Carbon nanotubes decorated by covalently linked gold nanoparticles have also been produced by this means. 

Gold nanorods were prepared by the photochemical procedure of Kim et al. [6]. Gold nanocrystals with an average diameter of 2.5 nm were obtained by the reduction of chlo-roaurate ion (0.55 ml of 25 mM aqueous solution) by partially hydrolyzed tetrakis (hydroxymethyl) phosphonium chloride (THPC) [7], CdSe nanocrystals were prepared by the solvothermal procedure starting with cadmium stearate, selenium and tetralin in toluene [8]. SWNTs prepared by the electric arc method with a Y2O3 + Ni catalyst, were purified by acid and hydrogen treatments [9]. 

In order to prepare SWNT-Au nanocrystal composites, SWNTs were functionalized by amidobutane (with a terminal azide group) as follows. Acid-treated SWNTS were reacted with thionyl chloride, followed by reaction with 4-azidobutylamine. These SWNTs were reacted with hexy-nethiol-capped Au nanocrystals. 

Photoluminescence spectra were recorded with a Perkin-Elmer LS-55 spectrometer while the UV-vis absorption spectra were recorded with UV/VIS/NIR Perkin-Elmer spectrometer. Transmission electron microscope (TEM) images were obtained using a JOEL JEM 3010 instrument. Infrared spectra were recorded with a Bruker IFS-66v spectrometer. 

In order to assemble gold nanorods (aspect ratio 2.4) by the click reaction, one batch of nanorods capped with 4-azidobutane-l-thiol, A, and another with hex-5-yn-l-thiol, B, were reacted in the acetonitrile-water mixture under standard conditions [12], The occurrence of the click reaction was established by infrared spectroscopy [13], The product of the reaction was investigated by electronic absorption spectroscopy and transmission electron microscopy. Fig. 1 compares the electronic absorption spectra of the gold nanorods before and after the click reaction between the A and B type nanorods. Isolated gold nanorods show transverse and longitudinal plasmon bands around 520 nm and 630 nm, respectively (see Fig. la). 

Corresponding author. Fax 4-91 0 23622760. E-mail address cnrrao jncasr.ac.in (C.N.R. Rao). 

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