Covalent and noncovalent modifications of single-walled carbon nanotubes

Single-walled carbon nanotubes (SWNTs) exhibit strong optical absorbance in the near infrared (NIR) range (700--1100 nm). Raw HiPco SWNTs, generated by the process of high-pressure disproportionation of carbon monoxide, were functionalized covalently with carboxyl groups via nitric acid reflux for 12 h to exploit their interesting opto-electronic properties exhibited at the nanoscale dimensions. The carboxylated SWNTs (C-SWNTs) yielded stable aqueous dispersions, while retaining partial optical absorbance, and through the carboxyl group enabled further functionalization with target specific chemical and biological sensing moieties for various applications. In this study, biotin-LC-PEO-amine, a hydrophilic, biocompatible tether has been demonstrated to covalently react with the previously generated carboxyl groups. Atomic force microscopy (AFM) characterization of the biotinylated SWNTs (B-SWNTs), combined with transmission electron microscopy (TEM) of Streptavidin gold labeled constructs revealed similar distribution of the biotin sites along the sidewalls of the SWNTs. UV-Vis-NIR and Raman spectroscopic methods were used to study the effect of covalent modification on the optical properties and structural morphology of the SWNTs. A sensitive polyacrylamide gel electrophoresis method was utilized to quantify the SWNT concentration in the dispersions using C-SWNTs as the calibration standard. Subsequently, a sensitive binding immunoassay was designed and demonstrated to target the B-SWNTs to Her-2 cell receptors on breast lymphoma cells. These B-SWNTs were directed to breast tumor cells, BT-474 using anti-Her2 monoclonal antibody (MAb) and NeutraAvidin(TM) to bridge between the MAb and the B-SWNTs. Immunofluorescence microscopy revealed the surface distribution of Her-2 receptors at 15 ºC and correlative confocal Raman imaging confirmed the surface binding of B-SWNTs. Photo thermal ablation of tumor cells was demonstrated by using NIR laser (810 +/- 10 nm) using carboxylated and B-SWNTs.;In the second chapter, SWNTs were noncovalently modified using a designed peptide, nano-1. Nano-1, an amphiphilic alpha-helical peptide, has demonstrated efficiency in dispersing hydrophobic SWNTs through pi-stacking interactions between the phenyl ring of phenylalanine residues and the SWNT surface. While the dispersal ability of these peptides has been demonstrated, we still need to understand the structure and orientation of these peptides on the SWNT surfaces. This knowledge is critical for the future design of new peptides exhibiting enhanced stability and efficient coating of SWNT surfaces. TEM tomography techniques and three dimensional reconstruction algorithms were developed to investigate the structural organization of this designed biomolecule on the SWNT surface. Tomography acquisition parameters were optimized including accelerating voltage, spot size, various tomography modulations ranging from automated, automated with manual focusing, low dose routine and focal series at a range of defocus values, etc. were tested in order to generate a quality data set. These results were compared to prior information obtained on dried samples by AFM, traditional TEM, and molecular dynamics computer simulations. A comparison of reconstruction computational algorithms by weighted back projection (WBP) on the IMOD tomography software and simultaneous iterative reconstruction technique (SIRT) on the FEI 3-D Express system was performed using the same alignment file generated by fiducial alignment on IMOD. Although WBP is open source, routine and straightforward method of reconstruction, the advantages of contrast restoration and noise reduction by SIRT have been illustrated. A trade-off between resolution in reconstructed tomogram and microscope magnification is defined. The concept of 'empty magnification' and its dependency on the microscope optics and camera resolution have been highlighted. Surface rendered 3-D modeling performed on ParaView modeling framework allowed 3-D visualization of the peptide coating on SWNTs. Details on suggestive thresholding with valid intensity range, contour mapping by joining points of same intensity and surface rendering to view a 3-D representation of the peptide-coated SWNT have been illustrated.