Comparison of the lowest detection of Zn²⁺ with various modification of the gold thin film.

Sensing layer	Lowest detection	Reference
Polypyrrole–chitosan	0.98 ppm	37
MMW chitosan (glutaraldehyde-crosslinked)	0.5 ppm	36
Immobilize metallothionein onto a carboxymethylated dextran matrix	0.13 ppm	35
Chitosan and chitosan–tetrabutylthiuram disulfide	0.1 ppm	38
Modified-nanocrystalline cellulose/graphene oxide	0.01 ppm	This study