Table 2.

Main characteristics of some types of pH sensors.

Ref.	Sensitive Material	Sensitivity (mV/pH)	Range	Linearity (%)	Drift (mV/h)	Hysteresis (mV)	Reference Electrode	Sensitive Area	FET Device	Type
[30]	ITO	58	2–12	nr	nr	9.8	SCE	6 mm2	CD4007UB	P
[32]	SnO2	56–58	2–12	nr	nr	nr	SCE	nr	CD4007UB or LF356N	P
[41]	TiO2	59.89	1.8–12	93.50	0.041692–2.6007	5.3–9	Ag/AgCl	1 cm2	NDP6060L	P
[42]	V2O5	58.1 ± 0.8	2–10	nr	nr	nr	nr	nr	CD4007UB	P
[92]	ITO/PET	50.1 ± 1.7	2–12	98.5	13.2	nr	Ag/AgCl	Π × 22 mm2	CD4007CN	P
[94]	ITO/PET	45.9–52.3	2.1–12.1	98.3–99.6	nr	nr	Ag/AgCl	Π × 22 mm2	CD4007UB	P
[95]	SnO2	59.3	2–9.4	nr	nr	nr	Ag/AgCl	nr	LT1167–I.A.	P
[101]	AZO	57.95	1–13	99.98	1.27	4.83	Ag/AgCl	2 × 2 mm2	CD4007UB	A
[104]	ITO/SiO2/Nb2O5	59.2	3–13	99.48	2%	1.83%	Ag/AgCl	20 × 20 mm2	IC4007	P
[106]	ZnO nano-array	45	4–12	nr	nr	nr	Ag/AgCl	Π × 2.52 mm2	CD4007UB	P
[108]	SnO2/SiO2/glass	58	1–9	nr	nr	nr	Ag/AgCl	1.5 × 1.5 mm2	LT1167–I.A.	P
[109]	SnO2/ITO/PET	53.8–58.7	2–12	nr	nr	nr	Ag/AgCl	nr	LT1167–I.A.	P
[113]	PdO	62.87 ± 2	2–12	99.97	2.32	7.9	Ag/AgCl	0.25 cm2	CD4007UBE	P
[114]	InGaZnO	59.5	2–10	99.7	3–9	nr	Ag/AgCl	nr	CD4007	P
[115]	Glass	55	2–12	nr	nr	nr	nr	nr	CD4007UB	P
[116]	CNT	50.9	3–13	99.78	nr	nr	nr	1 × 2 cm2	nr	P
[117]	FTO	54.10	2–12	nr	nr	nr	nr	nr	CD4007UB	P

PET, polyethylene terephthalate; AZO, aluminum-doped ZnO; P, potentiometric; A, amperometric; I.A., instrumentation amplifier; nr, not reported.