Table 1.

Summary of ZnO nanostructure-based intracellular metal ion-selective biosensors (PVC: Poly Vinyl Chloride; BGC: Borosilicate Glass Capillary).

Ref	[24]	[5]	[25]	[18]	[17]	[26]
Enzyme/Electrode	PVC/Ag wire	PVC/BGC	PVC/Ag wire	PVC/IBGC	PVC/BGC	PVC/BGC
Immobilization Mode	Physical adsorption	Physical adsorption	Physical adsorption	Physical adsorption	Physical adsorption	Physical adsorption
ZnO Synthesis	ACG	ACG	ACG	ACG	ACG	ACG
ZnO Morphology	Nanowires	Nanorods	Nanorods	Nanorods	Nanorods	Nanorods
Response Time(s)	<1 min	fast	20 s	fast	fast	fast
Ion-Selection	Ca2+	Ca2+	Ca2+	Na+	Mg2+	K+
Sensitivity (mV/decade)	26.4	29.67	113.92	72	26.1	41.47
Linaer Response Range	1 µM–0.1 M	100 nM–10 mM	1 µM–1 mM	0.5 mM–100 mM	500 nM–100 mM	25 µM–125 mM
Interfering Ions	No tested	No tested	Na+, Mg2+, K+	Ca2+, K+, Mg2+,	Ca2+, Na+, K+	No tested