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A nanoinjector for microanalysis.

We describe a simple miniature injection device that can be used for introduction of nanoliter sample volumes in microfluidic systems. The hybrid microstructure consists of two hydraulically connected parts, a pulse micropump, and a multilevel cross-flow injector. Sample injection is accomplished by creating a transient pressure pulse in the sample line by means of the solenoid-based micropump. The sample line is aligned at right angles to the main carrier flow line. The two flow channels are located in two different parallel planes. The cross section of the two channels is defined by a self-sealing aperture in an elastomer. During the pressure pulse, the sample is introduced through this aperture directly into the main flow stream. Fast impulse-based injection causes rapid mixing of the injected sample with the main flow stream. This permits simple single-line manifold micro flow injection (MFI) systems. The deformation/relaxation of the elastomer is fast and repeatable; as such, rapid serial actuations essentially result in a larger injected sample volume without significantly affecting the peak shape. In the present form, 2-40-nL samples are easily injected by single injection, and the injected volume can be chosen by system parameters. The injection repeatability as observed by a photometric detector is better than 1.2% (n = 100).