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.

More info on quantum Dots

We describe quantum dots, semi conducting nanocrystals roughly 5nm in size. They also have applications in the biological world as fluorescent tags Quantum dots are nanometer-scale nanocrystals composed of a few hundred to a few thousand semiconductor atoms made out of bio-inert materials – meaning they are non intrusive and non toxic to the body additionally unlike fluorescent dyes (which tend to decompose and lose their ability to fluorescence), quantum dots maintain their integrity withstanding more cycles of excitation and light emission before they start to fade. Changing their size or composition allows scientist to cater their compositions allows the scientist to cater the optical properties.-Which means they can fluoresce in a multitude of colors. This effect is called quantum confinement (hence the name the quantum dots)- they have quantized discrete energy levels that are directly related to their size.

Interestingly enough, quantum dots can even be tuned to fluorescence in different colors with the same wavelength of light. In other words it can choose quantum dots sizes where the frequency of light to make one group of dots fluoresce is an even multiple of the frequency required to make another group of dots fluoresce: both dots then fluoresce with the same wavelength of light. This allows for multiple tags to be tracked while using a singe light source.

A paul alivistos and his company (Quantum Dots corporation) have used these concepts in their Qdot product- a quantum dot surrounded by an inorganic shell that amplifies its optical properties while protecting the dot from its environment. The Qdot can have a variety of attachments to its shell. allowing it to attach to specific cell walls.- or even penetrate a cell and light it up from the inside. In the summer of 2003, This company joined forces with matsustha Electronic Industrial co(Panasonic) and sumitomo Corporation Biosciences to develop advanced optical and image processing technologies that utilize the Qdot. Products under this agreement are expected to generate revenue of more than $100 million per year for quantum dot Corporation by 2007.(Tiny product, big bucks)

An example of quantum dots in action involves targeting and imaging cancer cells. Researchers at Emory University, Georgia Tech and Cambridge Research and instrumentation have used quantum dots to identify tumors in mice. These quantum dots were made of cadmium selenide- zinc sulphide each 5nm in diameter. They were coated with polymers to prevent both the body from attacking the quantum dot and to keep the dots themselves from leaking toxic Cadmium and selenium ions.(Eek! Toxic! Read on...) Finally they attached antibodies to the outer shell that was first targeted and then attached themselves to a prostrate tumor cell surface. The scientist injected the quantum dots into the circulatory system and the dots accumulated at the tumor, which could then be detected by fluorescence imaging. As an added benefit, these quantum dots have a large surface area allowing for a dual role of both diagnostics and therapy.- the surface is big enough to attach both diagnostic and therapeutic antibodies to the surface.