NNT Quantum FAQ

1. Quantum dots are bigger than organic fluorophores. How does this affect their biological activity?

It is not clear how the size of quantum dots affects biological activity, but it is likely that conjugation of a quantum dot to a biological will dramatically decrease the diffusion coefficient of the conjugate. Furthermore, if the conjugation site is close to an active site or similar site in your biological, the large size of the quantum dot might inhibit binding. Because of this, NNT recommends the use of quantum dots in situations where quantitative measurements of binding coefficients etc. are not needed.

2. Do quantum dots penetrate cells?

Quantum dots can be up taken by cells through endocytosis but are otherwise not able to pass through the cell membrane. If imaging inside cells is desired, quantum dots can be either directly injected into the cell or conjugated to a membrane transport protein.

3. What is the surface chemistry of NNT’s Nano+ Dots? How will that affect my system?

NNT’s Nano+ Dots are encapsulated by a polymer with external carboxyl groups. These groups are highly charged at physiological pH and are necessary to prevent aggregation. Unless your system is sensitive to negatively charged ions, we expect Nano+ Dots will work well.

4. What is the best filter set to use for NNT’s Nano+ Dots?

It depends on the specific color of Nano+ Dot you are using. Your excitation filter needs to match your desired excitation wavelength. Normally our materials are best excited at 350 nm, 408 nm, 452 nm, or 488 nm – performance is better at the lower wavelengths. For emission, we recommend the use of Omega Optical filters (www.omegaoptical.com) as follows:

Blue: Use XF-3002. Note that the filter is not optimized for our excitation parameters and some emission may be lost by use of this filter.

Green: Use XF-3105.

Orange : Use XF-3094, which allows emission past 610 nm. This will eliminate crosstalk between Green and Orange QDs, assuming there are no other IR or deep-red emitters.

5. Are there any differences between conjugation of Nano+ Dots and conjugation of organic fluorophores?

Yes. First, unlike organic dyes, Nano+ Dots have many potential conjugation sites per fluorophore. Because of this, it is critical to carefully control the ratio of Nano+ Dot concentration to the protein of interest during conjugation. Second, quantum dots are larger than organic dyes – usually ~ 5-10 nm in size, which is similar in size to some proteins. This means that post-conjugation separation of unreacted protein and Nano+ Dots from conjugated Nano+ Dot-protein complexes can be difficult; NNT recommends trying multiple separation protocols for each conjugation.

6. What systems are Nano+ Dots best suited for?

Quantum dots in general – and Nano+ Dots in particular – are best suited for two kinds of applications. First, the high fluorescence intensity and lack of photobleaching make them ideal for high-sensitivity, low-count studies. Second, the availability of narrow emitters that are all excited by the same excitation source makes them ideal for multiplexing applications. Currently NNT has two separable colors in the visible spectrum for multiplexing applications, but we expect to have narrow emitters covering the entire visible spectrum in 2007.

7. Are quantum dots toxic?

No one is really sure. As far as toxicity to cell cultures, preliminary testing shows that fruit fly embryos exposed to Nano+ Dots continue to divide normally, suggesting limited short-term toxicity. However, Nano+ Dots are composed partially of cadmium telluride, which can potentially leach out of the Nano+ Dots. Cadmium is a known carcinogen and is highly toxic. Further, very little data exists on the toxicological properties of cadmium telluride-containing nanoparticles. Please take all appropriate precautions when working with Nano+ Dots and dispose of the materials properly. NNT will update our customers as further information becomes available, and up-to-date MSDSes are available.

8. What buffering systems can I use Nano+ Dots in?

Unlike some commercially available quantum dots, NNT’s Nano+ Dots are stable under high- and low-salt buffers and can be used in most common buffering systems, though the fluorescence intensity may vary. Buffers that contain complexing agents (such as EDTA), as well as MES-based buffers cause quenching of fluorescence, though Nano+ Dots still show measurable emission. Please contact us at info@nntech.com to ask about your specific buffer system.

9. Will Nano+ Dots stain glassware or other labware?

Yes. NNT recommends using disposable glassware whenever possible. To clean glassware that has been exposed to Nano+ Dots, use base bath or similar cleaning techniques.

10. Are there preferred storage conditions?

Not really. You will likely get longer shelf-life if they are stored cold (i.e. in the refrigerator) and in relative darkness. Having said that, we have not found NNT Nano+ Dots to aggregate under normal usage conditions.

11. What other kinds of nanoparticles does NNT sell?

NNT will be making a variety of nanoparticles commercially available in 2007. These will include colorimetric reagents, high-density scattering sources, and infrared-emitting fluorophores. If you have specific interests, please contact us at info@nntech.com.

For more questions, please contact us at info@nntech.com or by phone at (416) 260-8889 ext.221.