Fig. 3: Sensing performance of the 3D-printed sensor.

a The open-circuit potential (OCP) responses of the Ca²⁺-sensor. Standard solutions of Ca²⁺ were prepared in DI water; Ca²⁺ concentration was varied from 500 µm to 10.0 mm. The OCP was found to increase while the concentration of Ca²⁺ was increased from low to high. The same sensor was regenerated and tested for second-time measurements. The first and second sensings are separated by a dashed line border. The recording time for data collection was set to 100 seconds. b The calibration curves and slopes of the two successive sensing measurements of Ca²⁺. c OCP responses of the P-sensor. Standard solutions of P ions were prepared in DI water; P concentration was varied from 10.0 µm to 30.0 µm. The OCP was found to decrease while the concentration of P was increased from low to high. The same sensor was regenerated and tested for second-time measurements. d The resulting calibration curve and slope. Error bars in Fig. 3b and d is the standard deviation (SD) of three repeated measurements (n  =  3 biologically independent experiments). Error bars, mean ± SD. Deionized (DI) water is utilized as the solution for establishing the sensors’ baseline. Source data are provided as a Source Data file.