*3.2. Self-Assembled Monolayers (SAMs)*

Self-Assembled Monolayers (SAMs) are chemisorbed and ordered with various layers formed by the natural arrangement of thiolated molecules on the location of metallic interfaces. The most extensively used methods consist of SAMs with n-alkanethiols on noble metals [37], SAMs with carboxylate on the oxide surfaces [38], and SAMs with silane on the glass/silicon surfaces [39]. Xia et al., immersed the sidewall of the silica core into AuNSM colloid, forming a self-assembled AuNSM monolayer for sensitive wavelengthmodulated localized surface plasmon resonance (LSPR) for detecting the mercury (II) [40]. The label-free sensor obtained a very low LOD of 0.7 nM owing to the near field coupling improvement by the proximity distance of two types of gold nanoparticles-DNA conjugates.

#### *3.3. Covalent Attachment*

Covalent attachment is another approach for the covalent coupling to the ligand recognitions to electrochemical biosensor's interfaces, and improvements from the arrays of protein help form the most favorable conditions. A commonly used crosslinking molecule is carboxylic acid (C(=O) OH) groups on the electrode's surface as the biorecognition element with amine functional groups for exploiting the amide bond formation using the techniques of EDC/NHS chemistry. Likewise, this coupling approach has been effectively applied in various three-dimensional supports, such as agarose, aldehyde−agarose, and carboxymethylated dextran-based modified electrodes [41]. Carbon-based materials that reduce graphene oxide and carbon nanotubes can be adjusted with carboxylic acid through π−π stacking interaction. Furthermore, some researchers have lately proposed integrating covalent functional groups using diazonium chemistry [42].

#### *3.4. Electrodeposition*

The electrochemical deposition was crucial in preparing nanomaterials reliably and cost-effectively with mild physicochemical conditions. Furthermore, noble metals, mixed metal oxides, carbon materials, or conducting polymers can be deposited on the electrode with high deposition speed, straightforward scale-up techniques and commercial feasibility with standard maintenance. This method helps form the hybrid films with the controlled thickness and morphology, modifying the process parameters, controlling the bath conditions (solvent, pH, temperature), and effectively regulating the electrolyte formula [43]. For example, new properties immediately stand out when poly(3,4-ethylenedioxythiophene) associates with one or more components deposited as films [44]. Table 1 shows the various characteristics of the surface modification techniques for the BRE in electrochemical biosensors.


**Table 1.** Surface

modification

 techniques of BRE in

electrochemical

 biosensors.
