There is great interest in using single-walled carbon nanotubes (SWNTs) as nanoscale probes and sensors in biological electronics and optical devices because the electronic and optical properties of SWNTs are extremely sensitive to the surrounding environments. [1][2][3][4][5] For the applications of SWNTs-based sensors in a biological environment, an immediate question is how the sensors respond to the biological conditions such as pH, 5c glucose, various ions, and proteins. This study requires a well-controlled modification of SWNT surfaces to obtain interfaces that are sensitive to these variables. 6 The exploration in this exciting area is still not in full blossom, partially due to the difficulty in preparing water-soluble SWNTs while maintaining the SWNT electronic structure intact. 4 In light of recent great progress in solubilization of SWNTs in various solvents by polymer wrapping and sidewall functionalization, 3a,4,5b,7-10 a better controlled modification of SWNT surfaces may be realized soon. In this work, we report a facile chemical routine to prepare water-soluble SWNTs that still retain their van Hove singularities after oxidative treatment. 7 The solubility in water for as-treated SWNTs with modified surfaces provides us with a unique opportunity to reveal the relationship of their electronic and optical properties with pH. Here we observe that after surface modification with carboxylate groups, the optical absorption of asprepared water-soluble semiconducting SWNTs (Tube@Rice and HiPco) reversibly responds to the pH change.Purified pristine Tube@Rice SWNTs suspended in toluene were purchased from Rice University. Raw HiPco SWNTs were purchased from Carbon Nanotechnologies, Inc., and were purified by the method described in ref 11. Because similar results were obtained with these two types of SWNTs, we reported the results here only for Tube@Rice SWNTs for the sake of clarity.The facile routine for preparation of water-soluble SWNTs was a modification of the acid oxidative method developed in Smalley's group. 7 In a typical experiment, 14 mg of SWNTs were added into 5 mL of a 9:1 concentrated H 2 SO 4 /30% H 2 O 2 aqueous solution. The mixture was stirred for 30 min. After the reaction, 15 mL of the 9:1 concentrated H 2 SO 4 /30% H 2 O 2 solution was added into the mixture. Then the mixture was divided into six aliquots in test tubes. Each aliquot was placed in an ultrasonic bath (Branson model 1510) and was sonicated for a different period of time, ranging from 0 to 5.0 min. Each resulting SWNT dispersion was diluted using 250 mL of distilled water and then was filtered through a 0.4 µm Millipore polycarbonate filter membrane. The resulting six SWNT mats were continuously washed using 10 mM NaOH solution and distilled water until the pH of the filtrates was 7. Then the wet SWNT mats were separated from the filters by dispersing them in distilled water. Six aqueous solutions of the SWNTs (0.03 mg/ mL) were prepared by sonication for 1-2 min. No tube precipitation was observed from these solutio...

We have developed a simple, efficient process for solubilization of single-wall carbon nanotubes (SWNTs) with amylose in aqueous DMSO. This process requires two important conditions, presonication of SWNTs and subsequent amylose treatment in an optimum mixture of DMSO/H2O. The former step separates SWNT bundles, and the latter step provides a maximum cooperative interaction of SWNTs with amylose, leading to the immediate and complete solubilization. The best solvent condition for this is around 10-20% DMSO, in which amylose assumes a random conformation or an interrupted helix. This indicates that the amylose helix is not the prerequisite for encapsulation of SWNTs. The SEM and AFM images of the encapsulated SWNTs manifest loosely twisted ribbons wrapping around SWNTs, which are locally intertwined as a multiple twist, but no clumps of the host amylose are seen on SWNT capsules.

Excitation of localized surface plasmons in metal nanostructures generates hot electrons that can be transferred to an adjacent semiconductor, greatly enhancing the potential light-harvesting capabilities of photovoltaic and photocatalytic devices. Typically, the external quantum efficiency of these hot-electron devices is too low for practical applications (<1%), and the physics underlying this low yield remains unclear. Here, we use transient absorption spectroscopy to quantify the efficiency of the initial electron transfer in model systems composed of gold nanoparticles (NPs) fully embedded in TiO or AlO films. In independent experiments, we measure free carrier absorption and electron-phonon decay in the model systems and determine that the electron-injection efficiency from the Au NPs to the TiO ranges from about 25% to 45%. While much higher than some previous estimates, the measured injection efficiency is within an upper-bound estimate based on a simple approximation for the Au hot-electron energy distribution. These results have important implications for understanding the achievable injection efficiencies of hot-electron plasmonic devices and show that the injection efficiency can be high for Au NPs fully embedded within a semiconductor with dimensions less than the Au electron mean free path.