The electrical impedance of microelectrodes was measured in Ringer's solution in a twoelectrode setup with a Pt counter electrode in the frequency range from 100 Hz to 40 kHz.
The assembled fluidic probes were in addition hydrodynamically characterized by connecting them to a syringe pump (NE-300-ES, New Era Pump Systems Inc., Farmingdale, NY, USA) using commercially available fluidic connectors. The flow rate was increased from 200 to 1000 nl/min in multiple steps, and the fluidic pressure was recorded using a microfluidic pressure sensor (MPS4, Elveflow, France) equipped in the flow path.
In order to investigate the spatial distribution of a liquid injected from these probes as a function of flow rate, we applied 0.6% agarose gel as a suitable brain model (Z.-J. Chen et al., 2004) (link). The microfluidic probe was connected to a 10-µl glass syringe via thin tubings and a union, similar to the fluidic line in the experimental setup in Fig. 3(B). The probe shank was slowly inserted into a block of agarose gel, and 1 µl of 0.22-µm-filtered, 0.1% bromophenol blue solution was injected using the syringe pump NE-300-ES (New Era Pump Systems Inc.). Multiple injections were performed at flow rates of 50, 100, 200, and 400 nl/min, and the spread of dye was monitored with a microscope camera (MC190 HD, Leica Microsystems GmbH, Wetzlar, Germany).
The assembled fluidic probes were in addition hydrodynamically characterized by connecting them to a syringe pump (NE-300-ES, New Era Pump Systems Inc., Farmingdale, NY, USA) using commercially available fluidic connectors. The flow rate was increased from 200 to 1000 nl/min in multiple steps, and the fluidic pressure was recorded using a microfluidic pressure sensor (MPS4, Elveflow, France) equipped in the flow path.
In order to investigate the spatial distribution of a liquid injected from these probes as a function of flow rate, we applied 0.6% agarose gel as a suitable brain model (Z.-J. Chen et al., 2004) (link). The microfluidic probe was connected to a 10-µl glass syringe via thin tubings and a union, similar to the fluidic line in the experimental setup in Fig. 3(B). The probe shank was slowly inserted into a block of agarose gel, and 1 µl of 0.22-µm-filtered, 0.1% bromophenol blue solution was injected using the syringe pump NE-300-ES (New Era Pump Systems Inc.). Multiple injections were performed at flow rates of 50, 100, 200, and 400 nl/min, and the spread of dye was monitored with a microscope camera (MC190 HD, Leica Microsystems GmbH, Wetzlar, Germany).