Literature/202310101226 tracking magnetic beads in 3d

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Using Stereo Darkfield Interferometry (see paper: Stereo Darkfield Interferometry) it is possible to perform force-extension measurements by using magnetic nanoparticles under a magnetic tweezer.

The biggest advantage of SDI is that allows for multiple particles to be tracked at once:

images/Pasted image 20231010123220.png

In this case, the most relevant parameter is the position along the optical axis ($\hat{z}$) which is encoded in the rotation of the intereference pattern recorded on the camera.

Applications to DNA hybridization:

images/Pasted image 20231010123337.png

And helicase stepping:

images/Pasted image 20231010123418.png

Come as natural applications.

It is worth noting that the presence of brownian motion is the real limit to the accuracy of these measurements. magnetic tweezer does not have infinite stiffness.

The temporal resolution limit of the method comes from these thermal fluctuations than from the optical resolution itself or the data-transfer rate from the camera.


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Aquiles Carattino
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