Single-cell metabolomics holds the potential to deliver unprecedented insights in the functioning of cellular metabolism, as cells are the fundamental units of all biological systems. To address the challenge of analyzing metabolites at the single cell level, micro- and nanofluidic technology is critically needed due to the very small volumes and low number of copies of the various metabolites involved. This challenge can be faced by a multidisciplinary approach, in which technologies for cell handling, sampling, purification, preconcentration separation, and detection techniques are integrated in a versatile single cell analysis platform.
Within this context, a micro/nanofluidic concentration device, based on the phenomenon of concentration polarization, has been designed and characterized in order to find optimal concentration regimes. During characterization experiments with high analyte concentrations, it was discovered that charged compounds could not only be efficiently concentrated, but also separated in a manner very similar to the well-known technique of isotachophoresis (ITP). In contrast to conventional ITP, a discontinuous electrolyte system was not required. Instead, the depletion zone which forms during concentration polarization induced the separation. Hence this new method was named depletion zone isotachophoresis (dzITP).
To address the need of well-defined micro- and nanofluidic structures, an in-house process flow was set up for the fabrication of femtoliter rectilinear glass channels; actually, nanometer precision in the fabrication of these channels was achieved. This precision opens the perspective for analytically validated, robust methods that will enable unprecedented insight in the metabolic activity of single cells.