Preparation of iodine SWNTs and iodine US-tubes: Synthesis and spectroscopic characterization of iodine-loaded SWNTs for computed-tomography molecular imaging
Kissell, Kyle Ryan
Wilson, Lon J.
Doctor of Philosophy
This research presents the synthesis and spectroscopic characterization of I2-filled single-walled carbon nanotubes (I2 SWNTs) and I2-filled ultra-short carbon nanotubes (I2 US-tubes). These I2-internally-loaded SWNTs and US-tubes have applications both as a model system for the filling of SWNTs with other medically-interesting materials, such as alpha-radiotherapeutic radionuclides like At-211, and as synthons for a new class of computed-tomography (CT) X-ray contrast agents (CAs). Existing CT technology lacks the ability to diagnose critical diseases such as coronary artery vulnerable plaque, recently discovered as the cause of 70% of heart attacks, because current CAs circulate in the bloodstream rather than being targeted to specific cell-types. SWNT-based CAs offer several advantages over commercially-available CT CAs, such as the ability to sequester toxic ion and molecule imaging agents within the SWNT, to be targeted to specific cell types, and to translocate into targeted cells for intracellular molecular imaging. The synthesis of I2-SWNTs and I2-US-tubes is achieved via sublimation of molecular iodine (I2), a method proven to produce high yields for other filling materials. X-ray photoelectron spectroscopy (XPS) along with inductively-coupled plasma analysis (ICP-AE) and Raman spectroscopy have been used to define the location and quantify the amount of I2 in I2-SWNT and I2-US-tube samples. The exterior-adsorbed I2 can be removed (as I-) from I2-SWNTs by reduction with Na0/THF or by heating the I2-SWNTs to 300°C (without reduction), leaving I2 contained only within the interior of the SWNTs (I2 SWNTs). These I2 SWNTs contain ∼25 weight % of I2 and are stable without the loss of I2 even after exposure to additional reduction with Na 0/THF or upon heating to ca. 500°C. Micro CT experiments confirm that I2 SWNTs, with a radiodensity of 28,400 HU, are functional CT contrast agents. In contrast to I2-SWNTs, the internal I 2 in I2-US-tubes is unstable and is removed by either Na 0/THF reduction or temperatures of 300°C. To date, this instability has resulted in the inability to synthesize PEG-I2 US-tubes, a biocompatible water-soluble derivative of I2-US-tubes. However, initial experiments toward the synthesis of serinol-aide-I2 US-tubes have shown promising results, indicating a water-soluble derivative of I 2 US-tubes will be synthesized in the very near future. The I2 SWNTs and I2 US-tubes prepared in this research represent the first medical applications of filled SWNTs for CT imaging. I 2 SWNTs can now be used as a model system for the filling of SWNTs with other materials such as 211AtX (x = any halogen) for targeted alpha-radioimmunotherapy. They also signify the first step toward revolutionary intracellular CT imaging for the diagnosis of many diseases including coronary artery vulnerable plaque and cancer.