Fig. 3. Performance validation of four sensors in the cell culture monitoring system.

(A) Schematic illustration showing sensor configurations and working principles of each electrochemical sensor, consisting of reference electrode (RE), working electrode (WE), and counter electrode (CE). Ω, ohms. (B) Potentiometric pH sensor performance in different buffers (top), its sensitivity plot (middle; n = 5), and stability plot of the thin-film sensor up to 7 days, compared with a commercial sensor (bottom; n = 3). V, voltage. (C) Performance of resistive temperature sensors, showing the comparison with a commercial one (top; the negligible difference between the two sensors), the sensitivity plot (4.03 ohms/°C) (middle; n = 3), and the stability plot showing the measurement consistency for 7 days (bottom; n = 3). (D) Thin-film DO sensor’s performance under different DO concentrations from 0 to 15 parts per million (ppm; top), the sensitivity plot of the sensor (middle; n = 5), and the 7-day long measurement of DO (bottom; n = 5), compared with a commercial oxygen sensor under 8 ppm of O_2. (E) Performance of glucose sensors showing the current signal changes in saline with different glucose concentrations from 0 to 60 mM (top), the sensitivity plot of the sensors showing a linearity range to 60 mM (middle; n = 5), and the stability plot for 7 days when compared to a commercial one (bottom; n = 5). J, current density.