Table 2.

Representative results for synthesis methods and optical sensing applications of the gold- and silver-based nanomaterials.

	Synthesis Methods	$\mathbf{Optical}\mathbf{Sensing}\mathbf{Applications}$	Ref.
Gold-based nanomaterials	• Citrate reduction of gold precursor; Deposition of AuNPs on the ordered tellurium nanowire template.	•  Efficient SERS platform by highly ordered gold nanowire arrays. ➀ Anisotropic NP arrays. ➁ Polarization-dependent SERS.	[114]
	• Oblique incidence physical-vapor-deposition on pre-patterned rippled substrate by low energy ion irradiation.	•  Anisotropic SERS of gold nanowire arrays and NP chains. ➀ Comparative study of nanowire arrays and NP chains. ➁ Polarization-dependent SERS.	[103]
	• Chemical reduction of gold precursor with NaBH${}_4$.	•  Polarization-dependent SERS in gold nanoparticle-nanowire system.	[115]
	• Vapor transport method.	•  SERS sensing of benzenethiol ($BT$) by a single gold nanowire on a gold film. ➀ Nano-gap-enhanced Raman scattering. ➁ Polarization-dependent SERS.	[102]
	• Citrate reduction method.	• Single molecule and single living cell detections by AuNP-based SERS.	[106]
	• Citrate-stabilized AuNPs.	•  In vivo tumor targeting and SERS detection by scFv, EGFR-conjugated AuNPs.	[108]
	• CTAB-stabilized Au nanocubes by NaBH${}_4$ reduction of gold precursor.	• SERS sensing of human immunodeficiency virus (HIV) by Au nanocubes.	[116]
	• Citrate reduction method.	• SERS sensing of food-borne pathogens by biorecognition element-conjugated AuNPs.	[117]
	• Numerical simulation study.	• Influence of size, shape, and dielectric environment on the optical properties of metal NPs.	[23]
Silver-based nanomaterials	• Chemical reduction of silver precursor with ascorbic acid.	• Efficient SERS platform by self-assembled AgNP monolayer.	[118]
	• Plasma reduction of silver precursor.	• SERS sensing by AgNPs loaded on a polyester fabric by plasma jet printing.	[119]
	• Citrate reduction of silver precursor; Deposition of AgNPs on graphene nanosheets.	• SERS sensing of the freshness of fruits and vegetables by AgNPs and AuNPs supported on graphene nanosheets.	[113]
	• Citrate reduction method.	• Cancer detection by AgNP-based SERS.	[120]
	• Citrate reduction method.	• Single-molecule detection of rhodamine 6G by AgNP-based SERS.	[105]
	• Fabrication of Ag nanowires in highly ordered porous aluminum oxide (PAO) template by AC electrodeposition.	• Efficient SERS platform by Ag nanowire bundles.	[111]
	• Review for synthesis methods and plasmonic sensing applications.	• Synthesis methods and SERS/SEF sensing of AgNPs.	[109]