Methods we compared for attaching nanotubes to silicon AFM tips include manual assembly, direct growth and pickup.Smalley's group reported the first example of the use of carbon nanotubes as AFM tips in 1996. 1 They manually attached multi-wall carbon nanotubes (MWNT) and ropes of individual SWNTs to the apex of silicon pyramidal tips using tape adhesive and a micromanipulator in an optical microscope. The main drawback to this method is that MWNT tips large enough to be seen optically did not improve the resolution much beyond standard silicon tips when imaging isolated amyloid fibrils. 2 We found it fairly efficient to manually attach MWNTs to silicon AFM cantilevers with a 1000x optical microscope. In particular, the rate of assembly was quite high when a 15 V potential was applied between the silicon probe and the nanotubes. This resulted in nearly perfect and rapid alignment of the nanotube to the silicon tip. However, there was not a clear path to doing so with the thin SWNTs required for very high-resolution imaging.Lieber ,3,4 and Quate's 5 groups later showed that individual single wall carbon nanotubes could be directly grown by chemical vapor deposition (CVD) on the silicon tips themselves by first pre-coating the tip with a metal catalyst. In the CVD synthesis of carbon nanotubes, metal catalyst nanoparticles are heated in the presence of a hydrocarbon gas or carbon monoxide; the gas molecules dissociate on the catalyst surface and carbon is adsorbed into the particle. As the carbon precipitates, a carbon nanotube is grown with a diameter similar to that of the catalyst particle.Two techniques for direct growth have been reported. One involves creating nanopores at the apex of the silicon tip by etching with hydrofluoric acid. Catalyst particles are then deposited inside the nanopores. Carbon nanotubes grown via CVD from such a tip have an appropriate geometry for AFM imaging. While this approach enables fabrication of SWNT tips, the preparation of the porous layer in the silicon is time consuming and placement of the nanotube at the optimal location near the tip apex is

We have previously reported that 4−6 nm diameter single-wall carbon nanotube (SWNT) probes used for tapping-mode atomic force microscopy (AFM) can exhibit lateral resolution that is significantly better than the probe diameter when prone nanotubes are imaged on a flat SiO2 surface. To further investigate this phenomenon, accurate models for use in atomistic molecular dynamics simulations were constructed on the basis of transmission electron microscopy (TEM) and AFM data. Probe−sample interaction potentials were generated by utilization of force fields derived from ab initio quantum mechanics calculations and material bulk and surface properties, and the resulting force curves were integrated numerically with the AFM cantilever equation of motion. The simulations demonstrate that, under the AFM imaging conditions employed, elastic deformations of both the probe and sample nanotubes result in a decrease of the apparent width of the sample. This behavior provides an explanation for the unexpected resolution improvement and illustrates some of the subtleties involved when imaging is performed with SWNT probes in place of conventional silicon probes. However, the generality of this phenomenon for other AFM imaging applications employing SWNT probes remains to be explored.

A homoleptic phosphine adduct of thallium(I) supported by a tris(phosphino)borate ligand has been isolated and structurally characterized.

The observation of spectroscopic signals in response to mechanically induced changes in biological macromolecules can be enabled at an unprecedented level of resolution by coupling single-molecule manipulation/sensing using carbon nanotubes with single-molecule fluorescence imaging. Proteins, DNA and other biomolecules can be attached to nanotubes to give highly specific single-molecule probes for the investigation of intermolecular dynamics, the assembly of hybrid biological and nanoscale materials and the development of molecular electronics. Recent advances in nanotube fabrication and Atomic Force Microscope (AFM) imaging with nanotube tips have demonstrated the potential of these tools to achieve high-resolution images of single molecules. In addition, proof-of-principle demonstrations of nanotube functionalization and attachment of single molecules to these probes have been successfully made.Improved techniques for the growth and attachment of single wall carbon nanotubes as robust and well-characterized tools for AFM imaging are being developed. This work serves as a foundation toward development of single-molecule sensors and manipulators on nanotube AFM tips for a hybrid atomic force microscope that also has single-molecule fluorescence imaging capability. An individual single wall carbon nanotube (SWNT) attached to an AFM tip can function as a structural scaffold for nanoscale device fabrication on a scanning probe. Such a probe can have a novel role, to trigger specific biochemical reactions or conformational changes in a biological system with nanometer precision. The consequences of these perturbations can be read out in real time by single-molecule fluorescence and/or AFM sensing. For example, electrical wiring of single redox enzymes to carbon nanotube scanning probes will allow for observation and electrochemical control of single enzymatic reactions, by monitoring fluorescence from a redox-active cofactor or the formation of fluorescent products. Enzymes “nanowired” to carbon nanotube tips may enable extremely sensitive probing of biological stimulus-response with high spatial resolution, including product-induced signal transduction.