Design of Microcontroller Based Test Bench for a Multichannel Integrated Biosensor Chip

The planar microelectrode array (pMEA) is an important tool for non-invasive recording in the fields of neuroscience and biosensing. It can be used for extra-cellular measurement of the induced voltage on an electrode underneath a cell upon the occurrence of an action potential. With the principle of capacitive coupling, the sensed electrode signal amplitudes typically range between 100 μV and 1 mV, depending on the cell type. Due to the small amplitude of original neural signals, signal conditioning and processing microelectronics units are necessary to integrate with the pMEA sensor for achievement of best measurement performance. Introducing fully customized ASIC into the microelectrode array substrate provides an efficient solution, which establishes the possibility of creating the biosensor system on chip (SoC) with a large number of sensing-sites for simultaneous measurement without introducing significant noise from the signal conditioning and processing circuitry [1]. In this research work, we have developed a fully customized biosensor chip for sensing the propagation of action potentials. With the paralleled multiple sub-circuits, this prototype multi-site planar microelectrode array biosensor integrates 24 (4 × 6) microelectrode array sensing sites, 24 parallel analog neural signal buffers and a shared OTA based high gain amplifier on the same substrate. Figure 1 depicts the biosensor chip architecture and the functional blocks of the biosensor system setup. The prototyped biosensor chip was fabricated by MOSIS using AMI C5 0.5μm, double poly, triple metal layer CMOS technology. The electroless gold plating process post-CMOS processing and packaging techniques were applied to the biosensor chip to promote the biocompatibility and stability in the aqueous cell culture environment. To interface the biosensor chip with PC, a microcontroller based electronic system is necessary to implement the functions of A/D conversion, biosensor chip control signal generation, digital signal processing and data/command communication between biosensor chip and GUI software running on PC. In this research work, a Motorola ColdFire MCF5307 microcontroller based electronic system was setup to serve as the interface between the biosensor chip and PC, which realized the full functions listed above. The firmware running on MCF5307 microcontroller was implemented with ColdFire assembly language where on the PC client Matlab platform was chosen to simply the software design work.