Table 6.

The GQDs-based optical sensor for silver ion detection.

Type of GQDs	Synthesis Method	Starting Materials	Optical Method	Linear Range	LOD 1 (nM)	References
AgNPs/GQDs	microwave-assisted	GO nanosheets	Fluorescent sensor	0–100.0 nM	3.5	[90]
Am-GQDs	hydrothermal	dead leaves (carbon powder)	Photoluminescent probe	-	300,000	[91]
N-GQDs	microwave-assisted hydrothermal	glucose/ammonia	Fluorescent probe	0.2–40.0 µM	168	[92]
S-GQDs	hydrothermal	1,3,6-trinitropyrene	Fluorescent probe	0.1–130.0 µM	30	[93]
GQDs	pyrolysis	citric acid	Fluorescent probe	0.5–10.0 µM	180	[94]
GQDs	purchased	-	Ratiometric fluorescence sensor	0–115.2 µM	250	[96]

¹ where LOD is limit of detection. AgNPs: Ag nanoparticles, Am: amine-terminated, GO: graphene oxide, N: nitrogen, S: sulfur.