Table 6.

Desired features of SERS substrates, proposed by Natan [85] and Lin et al. [37].

Feature	Suggested Benchmark	Notes
High average enhancement	$>{10}^5$	Larger enhancements allow more sensitive and/or faster analysis.
Uniformity	Variations < 20%	Uniform and reproducible substrates make the work of the practitioner much easier, since one does not need to try several spots to find the most efficient one, and results are reproducible from substrate to substrate. Both these features are crucial if quantitative measurements are to be performed. Large areas are particularly useful with portable instruments, since they are normally not coupled to a microscope.
Reproducibility	Variations < 20%
Large area	Some mm2
Stability		Substrates should preserve a good performance for a sufficient time (say a month) after fabrication. Moreover, they should not be degraded by the solvents (or other agents) they get in touch with under working conditions.
Ease of fabrication/low cost of production		Low-cost and scalable fabrication methods for substrates are crucial for a widespread diffusion of the SERS technique.
Cleanliness of the surface		The surface of the substrate should not have residual contaminants from the fabrication process.