¹²⁵I-Hydroxylated-single-walled nanotubes

[¹²⁵I-SWNTols]

Background

[PubMed]

Optical fluorescence imaging is increasingly used to visualize biological functions of specific targets (1, 2). However, the intrinsic fluorescence of biomolecules poses a problem when fluorophores that absorb visible light (350–700 nm) are used. Near-infrared (NIR) fluorescence (700–1,000 nm) detection avoids the background fluorescence interference of natural biomolecules, providing a high contrast between target and background tissues. NIR fluorophores have wider dynamic range and minimal background as a result of reduced scattering compared with visible fluorescence detection. They also have high sensitivity, resulting from low infrared background, and high extinction coefficients, which provide high quantum yields. The NIR region is also compatible with solid-state optical components, such as diode lasers and silicon detectors. NIR fluorescence imaging is becoming a non-invasive alternative to radionuclide imaging in small animals.

Carbon nanotubes are made of C₆₀ fullerene carbon units, which respond to local dielectric changes without photobleaching (3, 4). They can be tuned in a range of wavelengths for NIR absorption, thus providing broad excitation profiles and high absorption coefficients. They can be coated and capped with hydrophilic materials for additional conjugation with biomolecules, such as peptides, antibodies, nucleic acids, and small organic compounds for in vitro and in vivo studies (5). Single-walled carbon nanotubes (SWNTs) have a diameter of 1–5 nm and a length of 300–1,000 nm, and they have been shown to be non-toxic to cells in vitro. However, there have been limited in vivo studies of SWNT toxicological and pharmacological profiles in small animals. SWNTs have been hydroxylated with KOH and radiolabeled with Na¹²⁵I to form ¹²⁵I-hydroxylated-single-walled nanotubes (¹²⁵I-SWNTols) for biodistribution studies in mice (6).

Synthesis

[PubMed]

Wang et al. (6) performed hydroxylation of SWNTs by incubating SWNTs (1.4 nm in diameter, 340 nm in length) with KOH for 1 h at room temperature. Hydroxylated SWNTs (SWNTols) were isolated with size-exclusion column chromatography. SWNTols were iodinated with Na¹²⁵I by the chloramine-T method for 5 min at room temperature. ¹²⁵I-SWNTols were isolated with column chromatography with a radiochemical purity of >96%. There are only five ¹²⁵I atoms per 100 SWNTols. SWNTols were estimated to have a molecular weight of >500,000 Da. No dissociation of ¹²⁵I ions from solutions of ¹²⁵I-SWNTols was observed at 11 days after labeling. Photoelectron spectroscopic measurement confirmed the presence of the C-I covalent bonds in ¹²⁵I-SWNTols.

In Vitro Studies: Testing in Cells and Tissues

[PubMed]

Yehia et al. (7) performed transmission electron microscopy (TEM) and confocal Raman spectroscopy using human HeLa cells after incubation with SWNTs for up to 60 h at 37°C. SWNTs were taken up by HeLa cells in a time-dependent manner with confocal Raman spectroscopy. TEM revealed that SWNTs were in intracellular vacuoles but not in the nucleus. SWNTs did not affect the growth rates of HeLa cells.

Animal Studies

Human Studies

[PubMed]

No publication is currently available.