Physics and Biology

Hi all, its me again ... :)

Two things to share here...

Science News - where to go
If you're interested in science, but wish to be spared the laborious technical details, go to New York Times Science page -- excellent, first class science journalism there.

Forget Discover and New Scientist -- I find their science reporting too inaccurate in terms of scientific details. However, The Economist (Science reporting) and Scientific American are excellent sources of science news.



Physics in Biology -- Biological Quantum Dots
Anyway, mainly wish to share with you something from Physicsweb.org (Biological Quantum Dots Go Live, Physicsweb, Mar2003) which is relevant with what has been mentioned during the last two talks -- one by Dr Monica Plisch (on quantum dots) and the other by Prof Mike Starck (bioflourescence imaging).

If you recall, Dr Plisch mentioned that quantum dots are particles that are nanometer sized (10^-9 m) and the size of the particles determine the colour with which they flouresce (rather than their molecular makeup). So a nano-sized gold particle could very well be red rather than, well, gold. :)

Gold Nanoparticles in Colloidal suspension (red, rather than, erm.. gold :)

She spoke about the quantum dots being used in bio-imaging due to their ability to flouresce brightly under UV light, making it suitable as an alternative to organic dyes, which tend to fade with time. Also, the range of wavelengths of light emitted by the organic dyes are spread out, making it difficult to use more than 3 or so dyes. In contrast, the light emitted by quantum dots are monochromatic (single wavelength) and adjustable (just inject different sized quantum dots), making it superior. However, the challenge was that most quantum dots were toxic (see cadmium selenide quantum dots - below) and cannot be used in aqueous medium.

All bottles contain Cadmium Selenide Quantum dots -- but in different particle sizes... Numbers give wavelength of light emitted in nanometers. Do you know which bottle has the smallest/largest quantum dots?

Prof Starck mentioned the jellyfish flourescence gene, which could be inserted into the ...erm, DNA(?)... of a cell, and the replication of that allows researchers to tag a particular part of the DNA and observe it on a large scale --- Bio students/teachers, pls correct me k? cos my bio knowledge stops at Sec4...

So this article on Physicsweb.org (Best of Physicsweb / Physics in Biology) says that

Biologists have long been eager to probe living cells in full colour over extended periods of time. Such a technique could reveal the complex processes that take place in all living organisms in unprecedented detail, such as the development of embryos.
.... ....

Existing imaging techniques use natural molecules that fluoresce, such as organic dyes and proteins that are found in jellyfish and fireflies.....
.... ....

Inorganic semiconductor nanocrystals - quantum dots - can get round .. problems [faced by using organic dyes]. .... a mixture of quantum dots of different sizes can be excited by a light source with a single wavelength, allowing simultaneous detection and imaging in colour. Turning these ideas from physics into biology, however, has remained a challenge because quantum dots cannot survive in water, and they must remain non-toxic.

Now a team of physicists and biologists led by Albert Libchaber and Ali Brivanlou at Rockefeller University in the US has produced new, biocompatible quantum dots and used them to image a live frog embryo (B Dubertret et al. 2002 Science 298 1759-1762). The researchers were able to "dress" quantum dots in an organic disguise that prevents them from coming into direct contact with the aqueous biological environment.

Showing an example of their successful research:

New biocompatible quantum dots are set to revolutionize biological imaging. In (a) a frog embryo has been imaged using conventional organic-dye techniques, and the signal is seen to fade in time. (b) Specially prepared quantum dots that were injected into another frog embryo at the same time fluoresce brightly for much longer.

I thought that it was interesting to read the article in the light of the talks given by the speakers. (They gave excellent talks, in my opinion. Too bad you didn't take the chance to ask more questions to Prof Starck. Fyi, I spoke to Dr Plisch and she was very impressed by the questions that were raised.)

So it is a current field of research and the interesting thing I feel, is its multi-disciplinary nature. '

• The physics is in understanding the electronic structure of the quantum dots (i.e. the energy levels of the electrons in the quantum dot) and hence the wavelength of light emitted.
  
  
• The chemistry is in the synthesizing of the quantum dots.
  
  
• The biology is in the application of the above in bio-imaging.
  
  
• And, all research carry socio-economical issues as well... such as its economical or medical potential, or perhaps just the issue of whether the poor frog that gets injected has to live with the quantum dots that doesn't stop glowing... :P
  

So, think of yourselves as students of science and not just a particular subject like bio or chem or physics... and do take some time to read the article here.

Enjoy!
mrkoh


PS: I appreciate comments, your thoughts, etc... do post them here or in the comments part. Else I'll feel like I'm talking to myself here... :)