info on quantum dots continued

I know what you’re thinking-“Rich, what’s with all this about toxicity and ee-king? We can’t have our imaging material causing more problems.” And, you’re right. The scientists have also thought of this and have done experiments mirroring the body’s environment to make sure quantum dots and their coatings are stable over a broad range of PH and salt conditions- Even hydrochloric acid. And they passed with (ahem) flying colors.

Carbon nanotubes also have this fluorescence quality. R.Bruce Welsman and his group at Rice University have determined that semi-conducting carbon nano-tubes fluoresce in the near –infrared spectrum and can be fine-tuned to different wavelengths by varying the nano-tube diameter. The near infrared spectrum is particularly important for biomedical applications but nothing in the human body fluoresces in this region of the spectrum: in effect, human tissue is fairly transparent. It’s especially handy that nanotubes also maintain their fluorescent properties inside living cells, with no adverse effects to the cell.

Down the road ,such carbon nanotube technology may be used along the same lines as the quantum dots.- you could end up wrapping the tubes with a specific protein allowing them to target cells (such as tumors) Along these lines a proposal by Michael Stranto and his team at the University of Illinois Urbana/Champaign(involving a glucose-detection optical sensor) looks especially promising. Here nanotubes are wrapped in a glucose oxidase and placed inside a small porous capillary (20 microns across by 1cm in length) the capillary pores are only big enough for glucose to penetrate. Once through the glucose promptly reacts with the oxidation solution changing the fluorescence properties of the nanotubes. This capillary is subsequently inserted just underneath the skin, but within range of being able to detect the near –infrared fluorescence, Imagine a patient with diabetes wearing a watch that periodically checks the fluorescence /glucose and sounds an alert if levels are too low or high- all without needles.

Unlike quantum dots, nanotubes don’t contain heavy metals, so they don’t raise any toxic issues. Additionally nanotubes can be fine-tuned to very narrow wavelength, providing fluorescence in a greater number of wavelengths, giving us greater flexibility( in other words nano colors to our palette) Such properties may give nano-tubes the advantage among products marketed as laboratory imaging markers.