| Microfabrication techniques have been widely used in biological sensing applications. Applying the technology of fabricating extremely small geometry structure and positioning it onto a biological sample with high precision, at a nanometer range generates a possibility of measuring electrochemical and electrical signals from individual cells or to a certain extent, individual organelles. The advantage of applying high positioning precision to probing small objects such as biological cells or organelles, utilized by Atomic Force Microscopy (AFM) may be very notable when one measures cell electrical properties. A strong capability of precise measurement shall lead researchers to new observations in biology, as well as much more extensive understanding of some of today's biological phenomena.; An electrochemically active cantilever supported probe is designed, fabricated and tested. This dedicated scanning probe system is composed of a mechanical deflection structure necessary for the AFM scanning and an electrochemical ultra-micro-electrode (UME) High-aspect-ratio (20:1) tip required for a high performance SECM. The probe array is also possible for multiple electrochemical measurement points. A metal layer and another insulator layer are deposited on these tip structures to make each probe selectively conductive. Finally, cantilever structures are shaped and released by etching the silicon substrate from the backside.; The system is particularly applicable for measuring biological samples in vivo. During the phase of designing and developing the system, we also designed and implemented a platform of individual cell measurement. The platform is a combination of micro-fabricated electrodes, a laser scanning confocal microscope (LSCM), an atomic force microscope (AFM) and an electrochemistry analytical system. Applying the system in aqueous environment with localized sensing, we measured various mechanical and electrical properties, including cell potential and membrane impedance. Also, with this single cell investigation platform, we have been able to measure transient current triggered by photosynthesis in individual chloroplast in plant cells. The capability of measuring such substance brings the possibility of collecting current from plant cells with their natural photosynthesis reactions, which could be potentially an innovative solar energy source in the future. |
