Development of a pressure-driven injection system for precisely time controlled attoliter sample injection into extended nanochannels

The rapidly developing interest in nanofluidics, which is used to examine liquids on an order that ranges from an attoliter to a femtoliter, correlates with the recent interest in decreased sample amounts, such as in the field of single-cell analysis. For general nanofluidic analysis, the fact that a pressure-driven flow does not limit the choice of solvents (aqueous or organic) is an important aspect. In this paper, an automated injection system using a pressure-driven flow for several hundred nanometer-sized channels (extended nanochannels) is described. By automatically, and independently, switching four pressure lines using solenoid valves controlled by a sequencer with a time resolution of 10 ms, 550 aL sample band in minimum was reproducibly injected under normal phase conditions. The reproducibility of the band injection was improved by one order when compared with the previous injection method, which enables determination of time zero for injection. These facts are essential for the further band analysis in nanochannels, where diffusion is dominant. This injection system using pressure-driven flow can be used with any kind of solvent, which should make it a significant tool for nanofluidic applications, such as immunoassay, DNA analysis, and chromatography.