**3. Commercially available SERS substrate**

*Assorted Dimensional Reconfigurable Materials*

described and discussed in details below.

vantages of that approach are presented.

than the range of mm2

is random and unique.

great accuracy

**2. Conventional SERS substrate fabrication methods**

ods of that substrate are briefly summarized below.

after annealing can act as a semiconductor and be used, for example, as a photocatalyst for removal of residual particles left on the substrate after SERS measurements. Due to the listed above advantages, the anodic oxides in SERS applications become more and more popular but up to now only in the research area. It is worth to notice that aluminum and/or titanium anodic oxides as a SERS substrate are no commercially produced now, so as a consequence its fabrication methods can be classified as unconventional fabrication SERS substrate method. The possibilities of application of anodic aluminum oxide and anodic titanium oxide as SERS substrates will be

Conventional SERS substrate types are nanostructures covered by metallic nanoobjects (NS/PLA), including nanoparticles or colloids. The fabrication meth-

substrate production is connected with fabrication cost of nanostructures on large area [33] and resolution [34] of this technique. Below, in **Table 1**, the main disad-

The use of Au, Ag, or Cu metal colloids, with a diameter in the range of 10–80 nm, which are produced by chemical reduction, requiring the use of expensive chemical reagents, but the largest enhanced SERS (up to 1014), is shown for highly aggregated colloids [31]. The biggest disadvantages of using colloids are storage (usually they should be used immediately after preparation), difficulties in use in portable spectrometers, high cost, problems with repeatability, and the limited range of materials that can be determined due to colloids' dimensions. The use of colloidal metallic particles or nanowires on a glass substrate ensures a relatively homogeneous size of nanoobjects; however, their placement on the substrate

Since few years, the interest on new kind of flexible SERS substrates grows linearly. The new interesting group of SERS substrates constitutes flexible and highly sensitive multiparticle complexes. They are mainly based on metal nanoparticles

**Advantages Disadvantages**

*Main positive and negative features of using lithography methods in SERS substrate production.*

• The possibility of controlling the metal nanoparticles' size and shape as well as the interparticle distance with

• Good reproducibility at a molecular resolution range

The SERS substrates in a type of nanostructures covered by metallic nanoobjects (NS/PLA) are produced by the application of the physical vapor deposition (PVD) technique of thin discontinuous metallic layers on nanostructures [30], using lithographic techniques (photolithography, electron or ion beam lithography) [31], nanoprinting or lithography supported by a template (matrices of porous polymers or shadow lithography—nanosphere lithography (NSL)) [31]. However, the methods listed above are relatively expensive and time-consuming for areas larger

[32]. The limitation of using lithography method in SERS

• Expensive equipment

substrate

• Many steps are required to prepared one

• Quite long processes, so long manufacturing time for higher areas than nm2 • High cost for areas larger than few μm2

• Mass production is doubtedly

**64**

**Table 1.**

There are several commercially available SERS substrates. They are manufactured based on silicon etching and metal deposition techniques (Klarite substrates (discontinued), Renishaw), colloid distribution on cellulose fiber substrate (Ocean Optics substrate), or ion etching (Silmeco substrates). For more information on these solutions, see **Table 2**. All data were taken from the companies' websites.



**Table 2.**

*Commercially available SERS substrates with company name, main features, and oriented price.*
