Table 7.

The currently reported SERS substrates for sensing metal ions and their substrates, metal particles, target substances, and performances.

Ref.	Substrate	Metal Particles	Aptamer	Substance and Matrix	LOD	Linear Range
[170]	lateral flow strip	Au@Ag NPs decorated with R6G	DNA oligonucleotide	Hg2+ in DI water and tea	DI water: 0.36 pM Tea: 0.35 nM	DI water: 0.05 nM~1.0 nM, R2 = 0.989
[171]	Si wafer coated with monolayer Ag nanocrystals	Ag nanocrystals	4,4′-dipyridyl	Hg2+ in Ultra-pure water and tap water	Ultra-pure water: 0.35 fM	Ultra-pure water: 5 × 10−15 M~1 × 10−10 M
[172]	Etched Si wafer	Au nanorod arrays	No	Hg2+ in DI, ground and lake water	DI water: 0.1 nM Ground and lake water: 10 nM	DI water: 1 × 10−5 M~1 × 10−10 M, R2 = 0.984~0.998
[173]	Filter paper	Au nanoisland	No	Cd2+, Cu2+, and Ni2+ in rice	Cd2+, Cu2+, and Ni2+ in rice: 1 × 10−6 M	Cd2+, Cu2+, and Ni2+ in rice: 1 × 10−2 ~1 × 10−6 M
[174]	Au@Ag NR solution	Au@Ag nanorod	No	Hg2+ in DI water and egg	0.001 ng/mL	In DI water: 0.005~1 ng/mL, R2 = 0.9974