Literature/202212091127 iscat for refractive index of evs

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To overcome some of the limitations of nanoparticle tracking analysis, this paper leverages the use of iSCAT to measure the refractive index of particles, and to measure the size of smaller objects. The biggest advantage of using iSCAT over light sheet for a nanoparticle tracking analysis measurement is the superior signal to noise ratio for smaller particles. Interferometric measurements scale like $d^3$ instead of $d^6$.

Moreover, a smaller response to diameter allows to extend the dynamic range of the instrument. The setup is the traditional iScat setup using a $\lambda/4$ waveplate in combination with a polarising beamsplitter.:

iScat Setup for nanoparticle tracking


The objective is placed $1\mu m$ above the substrate and is stabilized with an active focus-lock.

Comparison with other methods

images/Pasted image 20221228140849.png The image above is the result of measuring size of 30nm gold particles with 4 commercially available instruments (DLS, TEM, SEM, and NTA) plus the custom iNTA setup. It is surprising that iNTA has a resolution similar to that of TEM, considering they are only exploiting the diffusion coefficient measurement to calculate diameter.

In the text, the authors claim that they use traces with at least 25 localization points and use a track-length weighted distribution. Sadly they don't fully comment on how they manage to to get a $3X$ improvement on the data generated by NTA, since the root of the measurement is the same. Can it be simply a better localization accuracy given by a larger frame rate? images/Pasted image 20221228140744.png


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