Limits of miniaturization: Assessing ITP performance in sub-micron and nanochannelsElectronic Supplementary Information (ESI) available. See DOI: 10.1039/c2lc21011h

The feasibility of isotachophoresis in channels of sub micrometer and nanometer dimension is investigated. A sample injection volume of 0.4 pL is focused and separated in a 330 nm deep channel. The sample consists of a biomatrix containing the fluorescently-labeled amino acids glutamate and phenylalanine, 20 attomoles of each. Isotachophoretic focusing is successfully demonstrated in a 50 nm deep channel. Separation of the two amino acids in the 50 nm deep channel however, could not be performed as the maximum applicable voltage was insufficient. This limit is imposed by bubble formation that we contribute to cavitation as a result of the mismatch in electro-osmotic flow, so called electrocavitation. This represents an unexpected limit on the miniaturization of ITP. Nonetheless, we report the smallest isotachophoretic separation and focusing experiment to date, both in terms of controlled sample injection volume and channel height. Isotachophoresis was succesfully miniaturized in sub-micron channels for the first time. An unexpected limit on upon further downscaling in nanochannels was encountered: The new phenomenon of electrocavitation.