Low-cost fabrication of a pH sensor based on writing directly over parchment-type paper with pencil

Herein, we introduce a low-cost and straightforward method for preparing pH sensors based on parchment-type paper and pencil traces as a base and electrode, respectively. The hydrophobic feature of the parchment paper supports the relatively long life of the proposed pH sensor. The results indicate that the present sensors have a Nernstian response with a Nernstian slope of 52.1 ± 1.5 mV/pH and a good linearity of 0.995 from pH 4 to 10. The stability of the proposed electrode is approximately 0.75 mV/h. The prepared electrodes show a relatively long operating life compared with the published results of ordinary paper-based pH devices. However, the Nernstian factor decreases over time and stabilizes at approximately 28 mV/pH after two months. This approach provides a low-cost and reproducible pH sensor.