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Micronit developed chips with nanofluidic channels (depth down to 100 nm) for Delft University. Please find below a short description of the research for which these chips have been developed.
A pressure-driven flow inside a nanofluidic channel carries with it the electrical counter charges that are induced by the charged channel walls. The electrical current that is generated in this way is called a streaming current, and can be used to deduce the effective charge density of a surface [1].
Charge Inversion
We used the method of streaming currents to study the effect of charge inversion in rectangular silica nanochannels [2]. Charge inversion is the phenomenon that the effective surface charge flips sign due to excessive accumulation of counter ions in the Stern layer close to a charged surface. This effect has been suggested to facilitate the attraction between like-charged objects, and as such can be biologically relevant in, e.g., DNA condensation, viral packaging and drug delivery. Charge inversion is known to occur for tri- and tetravalent ions.
We found conclusive evidence that charge inversion also occurs at high concentrations of divalent ions. Moreover, charge inversion by trivalent ions was found to disappear when large concentrations of monovalent salt were added. This observation was explained by a theoretical model.
References
[1] F.H.J. van der Heyden, D. Stein and C. Dekker, Phys. Rev. Lett. 95, 116104 (2005)
[2] F.H.J. van der Heyden, D. Stein, K. Besteman, S.G. Lemay and C. Dekker, Phys. Rev. Lett. 96, 224502 (2006)