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amblivious writes:
"A team from the University of Queensland has demonstrated quantum imaging inside living cells for the first time. They were able to map structures within cells at scales as fine as 10nm, offering a 14% resolution enhancement over coherent light. Conventional optical imaging is limited by diffraction but by generating the photons with a more consistent phase as squeezed light the amount of diffraction can be minimized.
The ability to map living cells at this scale represents a significant breakthrough in imaging. These methods promise to reveal important new levels of cellular complexity and deliver profound benefits to biotech and medical research, and 'confirm the longstanding prediction that quantum correlated light can enhance spatial resolution at the nanoscale and in biology.'"
(Score: 5, Informative) by bd on Saturday February 22 2014, @01:25PM
The summary is a bit hard to understand, and - I think - partially wrong. For those of you who want to understand what they did, I will try to explain it in simple terms.
They made a better version of a photonic force microscope. PFM's work a bit like atomic force microscopes. AFM's use a probe with a fine tip to mechanically scan a sample at atomic resolution. A PFM uses optical tweezers to move around a nano-particle as a probe. That's nice because you can do it inside a living cell.
The optical tweezers technique works because dielectric nanoparticles will tend to align to the electrical field of a tightly focused light beam. The shape of the electrical field means that the nanoparticle will see a small force that moves it to the center of the focused beam with high precision.
They basically move the nano-particle to different places in the cell and observe it's motion. Thereby, they learn something about the properties of the cell at that place. The precision, of course, is affected by noise in the light of the tweezer. Because of that they use a light source with low noise.
A problem is that the quantized nature of photons introduces a fundamental limit to the amplitude noise of your laser beam. This is because you cannot use a lot of photons because you generally don't want to burn your biological sample.
Now, there are two kinds of noise in monochromatic laser radiation: amplitude noise and phase noise. Interestingly, both are coupled. Using quantum optics, we can exchange phase noise for amplitude noise and vice versa.
The summary is wrong in saying that they lowered phase noise and increased amplitude noise, they did the opposite, see: http://www.rp-photonics.com/amplitude_squeezed_lig ht.html [rp-photonics.com]. Thereby they could lower the noise floor by some percents, enhancing the resolution in comparison to a PFM illuminated with a simple coherent light source.
Of course, this was only a demonstrator and they only moved the particle along a linear path. A proper microscope would have to add two more dimensions to actually scan the whole cell.
(Score: 2, Interesting) by NovelUserName on Saturday February 22 2014, @06:06PM
From a quick scan of the article, it appears that this technique is frequently used to probe the mechanical environment at very high resolution: i.e. bounce the probe molecule off of the item of interest and see how stiff it is. Since structural scanning relies on moving a single probe molecule over the 3d surface the technique doesn't seem particularly suited to whole cell imaging. It may be very useful for very fine/local structures such as the shape of specific transport channels in the cell membrane, or binding proteins attached to organelles etc.
(Score: 3, Interesting) by bd on Saturday February 22 2014, @07:30PM
Well, you are probably correct. Replace "whole cell" with "region of interest".
I was actually also wrong about them being only able to scan the particle along a line.
One problem with their technology demonstrator right now is that they only know the position of their particle in the x direction. The y and z directions are actually random. This means that their particle took a different, unknown trajectory through the cell for each \alpha-scan.
To conclusively demonstrate their resolution enhancements by showing a detailed picture of something, they now have to build a proper 3D-PFM. I guess they just wanted to publish something before someone else does.
(Score: 1) by NovelUserName on Saturday February 22 2014, @09:15PM
I'm nowhere near an expert in the field, but it sounded like the random motion was utilized as a feature (or at least they could derive useful info from it). Basically their apparatus could detect the motion and use that to identify the mechanical properties of the environs.
(Score: 1) by bd on Saturday February 22 2014, @10:32PM
They only tracked the particle in the x direction in their coordinate system, not y or z.