Detecting Bacterial Cell Viability in Few µL Solutions from Impedance Measurements on Silicon-Based Biochips

Abstract

Using two different types of impedance biochips (PS5 and BS5) with ring top electrodes, a distinct change of measured impedance has been detected after adding 1–5 µL (with dead or live Gram-positive Lysinibacillus sphaericus JG-A12 cells to 20 µL DI water inside the ring top electrode. We relate observed change of measured impedance to change of membrane potential of L. sphaericus JG-A12 cells. In contrast to impedance measurements, optical density (OD) measurements cannot be used to distinguish between dead and live cells. Dead L. sphaericus JG-A12 cells have been obtained by adding 0.02 mg/mL of the antibiotics tetracycline and 0.1 mg/mL chloramphenicol to a batch with OD0.5 and by incubation for 24 h, 30 °C, 120 rpm in the dark. For impedance measurements, we have used batches with a cell density of 25.5 × 108 cells/mL (OD8.5) and 270.0 × 108 cells/mL (OD90.0). The impedance biochip PS5 can be used to detect the more resistive and less capacitive live L. sphaericus JG-A12 cells. Also, the impedance biochip BS5 can be used to detect the less resistive and more capacitive dead L. sphaericus JG-A12 cells. An outlook on the application of the impedance biochips for high-throughput drug screening, e.g., against multi-drug-resistant Gram-positive bacteria, is given.

A Novel Approach to Monitor the Concentration of Phosphate Buffers in the Range of 1 M to 0.1 M Using a Silicon-Based Impedance Sensor

“…The carrier concentration values of N A and N D are 400 × 10 15 cm −3 and 2.5 × 10 15 cm −3 , respectively. The carrier concentration and built-in potential are referred from our previous work [ 18 ]. After filling 20 μL of phosphate buffer with a pipette inside the ring electrode, the values are varied in the similar range to model the total impedance of the system once the sample reaches equilibrium with the phosphate buffer liquid.…”

“…This approach allowed us to evaluate the impedance chip’s performance across different pH conditions as well as with different volumes. The pn junction silicon impedance chip has previously been applied in bacterial cell counting applications [ 17 , 18 ]. Furthermore, Poltorak et al [ 19 ] have utilized the doped silicon chips in investigating the lipid vesicles and polyelectrolyte interactions after impedance measurements in the frequency range from 100 kHz down to 100 mHz.…”