Improvements in the performance of an incubation-type planar patch clamp biosensor using a salt bridge electrode and a plastic (PMMA) substrate

Incubation-type planar patch clamp biosensors, first described in 2008, are expected to enable the realization of high-throughput neural network screening. Several technical challenges must be overcome before this technique may be implemented. First, it is difficult to achieve a sufficiently high seal resistance (a gigaohm seal), which is an important parameter for patch clamp operation. A low seal resistance produces large baseline fluctuations corresponding to the fluctuation of the solid–liquid and liquid–liquid interface potentials. Second, the sensor cell must be positioned at a micropore over a long incubation time while maintaining the cell viability. Finally, a low-cost high-performance sensor chip suitable for high-throughput screening must be developed. These problems have been resolved to some extent in the present work. A stable electrode with a salt bridge structure was developed here to reduce the baseline fluctuations. The cell positioning technology was improved by forming a novel cell trapping pattern using hot embossing on a plastic (polymethylmethacrylate (PMMA)) substrate for use in a microfluidic sensor chip. The combination of the stable electrode and the cell trapping pattern dramatically increased the device success probability from ∼2% to 60–80% using HEK293 cells as a model system. The utility of the present results was tested by characterizing rat hippocampal neuron networks. The seal resistance was found to be lower than the seal resistance obtained from the HEK293 cells. The effectiveness of the stable electrodes, however, was significantly clear and spontaneous channel currents from the neural network were successfully observed.