Properties of metal oxides based pH sensors for wearable/flexible electrochemical sensor fabrication.

Material	Fabrication	Substrate	pH range	Response time	Sensitivity (mV pH−1)	Flexibility	Ref.
IrO2	Sputtering	PET	4–7	—	61 ± 1	—	195
IrO2	Electrodeposition	PI	4–9	0.5 s	69.9 ± 2.2	—	184
IrO2	Sol–gel	PI	1.5–12	0.9 to 2 s	51	Tested in a tube with a 1 cm curvature radius	196
CuO nanorectangle	Hydrothermal synthesis	PET	5–8.5	—	0.64 μF pH−1	Tested in a tube with a 5 mm curvature radius	22
ZnO nanowalls	Low temperature	PI	1–9	—	∼59	—	197
	Polycrystalline silicon thin film transistor technology
IZO	Sputtering	PET	4–10	5 ms	105	Tested by bending around a cylinder with a 1.0 cm curvature radius	198
ITO	Radio frequency sputtering and a roll-to-roll process	PET	2–12	—	50.1	—	199
InGaZnO	Sputtering and thin film transistor technology	PI	3.3–11	—	51.2	Tested as a function of bending with up to 13 mm curvature radius	185
WO3 nanoparticle	Electrodeposition	PI	5–9	23–28 s	−56.7 ± 1.3	—	186