Surface characteristics and electrical properties of PMMA chips for incubation-type planar-patch-clamp biosensors

Polymethylmethacrylate (PMMA) plates were successfully applied as sensor chips in an incubation-type planar patch clamp (IPPC). Hot embossing both sides formed the PMMA plates, and a focused ion beam realized micropores. The low seal resistance of the IPPC was investigated by analyzing the surface roughness of the chips. Atomic force microscopy (AFM) showed that the chip surface had a roughness of several nanometers due to the molding process. Coating the molded surface with an anti-adhesive compound further increased the surface roughness of the PMMA chip because the anti-adhesive compound itself had a large roughness and in some case, the compound partially peeled off while detaching the mold. Similarly, coating a chip with extracellular matrix (ECM) poly-l-lysine (PLL) also increased the surface roughness. The measured seal resistance of the PMMA chip for an HEK293 cell was in the range of 4-15 MΩ. The low seal resistance was attributed to the sharp-edge structure of the micropore and the surface roughness of the chip. Nevertheless, the whole cell current was successfully recorded from HEK293 cells expressing channel rhodopsin wide receiver (ChRWR) using salt-bridge-type stable Ag/AgCl electrodes. Another advantage of the PMMA sensor chip was the small parasitic capacitance.