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Research project: Pores, Bubbles and Nanopores

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Sizing bubbles and particles can be problematic. There are several useful techniques. One of which is the use of Coulter counting technology.

Here, as a particle or bubble passes through a channel, the resistance of the structure changes. This change in resistance can be used to gather information on the motion and size of the particle within the media. We have used a set of micro1 and nanopores2 to follow particles and bubbles within liquids. The figures below show the motion of gas bubbles through a micropore and the corresponding changes in resistance.

Left image shows a gas bubble approaching and then travelling through a glass micropore. Right shows the change in current as the bubble translocates and the associated change in resistance in this case.

Depending on the size of the particle and the architecture of the pore, a resistance change of the media can be monitored.  However, as the particle gets smaller the change is resistance also diminishes.  To improve the system, the Birkin group developed a new sensing strategy utilising a ‘time shift’ approach3.  Here the signal from the pore is essentially split into two paths.  In one, no change is imposed while in the other a low pass filter is applied to the signal.  The resultant response is subtracted from the original and the result amplified.  This was shown to give improved sensitivity over a standard analysis.

(a) Shows a particle translocating through a pore. (b) Shows the ‘fast’ and ‘slow’ signals.  Note the slow signal is passed through a low pass filter. (c) The result of the subtraction of the fats and slow signals. (d) The amplified signal and (e) a final ‘self servo’ approach to ensure all data is essentially zero in the absence of a translocation.

  1. P. R. Birkin, S. Linfield and G. Denuault, PCCP, 2019, 21, 24802–24807.
  2. P. R. Birkin, S. Linfield, J. J. Youngs and G. Denuault, J. Phys. Chem. C, 2020, 124, 7544–7549.
  3. P. R. Birkin, S. Linfield, G. Denuault, R. Jones, J. J. Youngs and E. Wain, ACS Sensors, 2019, 4, 2190–2195.


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