Fig. 2.

(A) Fluorescence image of the on-chip injection protocol using a 4x objective. Sample has been spiked with 200 μM fluorescein. Both sample and buffer streams come into parallel contact for 300 μm but do not mix due to laminar flow. The buffer flow rate (2.5 μL min⁻¹) is greater than the sample flow rate (1.5 μL min⁻¹) to ensure no leakage of sample into the buffer channel. (B) The injection event after actuation of the off-chip 6-port injection valve (2.00 s actuation). The buffer flow stream is impeded allowing a portion of sample to pressurize into the buffer channel before the buffer stream is restored and a discrete plug of sample is carried down stream to the electrode.