Silicon based Impedance sensor for buffer concentration measurement and bacterial detection

Accurate and rapid determination of post-diluted aqueous biological buffer concentrations is important for maintaining pH stability, biochemical reactions, and cell membrane integrity. This dissertation presents the development and application of silicon-based impedance chips for buffer concentration measurement and bacterial detection. Two novel p-n junction-based chips, boron implanted (BG) and phosphorous implanted (PG), with a ring top electrode design, were developed as a reagent-free, rapid, and sensitive approach for determining buffer concentrations. Impedance measurements were first performed on phosphate buffers with pH values of 5.50, 6.38, and 7.12 at different dilution concentrations, followed by measurements on six biological buffers above and below physiological pH. Test volumes of 20–40 μL were analyzed in the frequency range of 40 Hz to 1 MHz. The impedance data were modeled using a self-developed multiparameter equivalent circuit model. A circuit parameter, RAu/Si, showed a systematic linear trend on a semi-logarithmic scale independent of pH, volume, and buffer type. The chips were further explored for bacterial viability screening using Lysinibacillus sphaericus JG-A12. The PG chip detected more resistive and less capacitive live cells, while the BG chip identified less resistive and more capacitive dead cells. These findings demonstrate the versatility of silicon-based impedance chips for buffer monitoring, label-free bacterial viability screening, pharmaceutical quality control, and future automated biosensing applications in diagnostics and environmental microbiology.