*2.5. Biomarker Detection on Other 2D Materials Conjugated with Metal Nanoparticles*

2D materials such as graphitic carbon nitride, black phosphorous, 2D layered double hydroxides (LDHs), boron nitrides, graphdiyne, etc. have also been explored in conjunction with metal nanoparticles for immunosensor applications with interesting biomarker targets (Figure 21, Table 5). Graphdiyne, the new 2D carbon allotrope with its unique sp-sp2 carbon network and highly π-conjugated structure has been receiving increased attention [163]. A graphdiyne-based self-powered biosensor platform was constructed by Hou et al. [164] for the determination of miRNA-21. Here, both the cathode and bioanode were fabricated by different modifications of AuNPs/GDY (Figure 21A). The 2D hexagonal boron nitride nanosheets, due to their electronic conductivity and large surface area were explored for immunosensor applications [165]. A label-free aptasensor for the detection of cardiac biomarker myoglobin on AuNPs decorated 2D-Boron nitride nanosheets was reported by Adeel et al. [166]. Here, the boron nitride nanosheets modified electrode AuNPs/BNNSs/FTO acted as a transducer for the immobilization of thiol-functionalized DNA aptamer for the specific binding of myoglobin (Figure 21B). Carbon nitrides are polymeric materials mainly consisting of carbon and nitrogen [167,168]. At ambient temperature, graphitic carbon nitride (g-C3N4) is the most stable allotrope of carbon nitrides. Due to the presence of basic surface groups and rich surface properties, g-C3N4 is attractive for many applications including catalysis [169]. Neto et al. [170] fabricated a miniaturized PEC system based on AuNPs decorated g-C3N4 for the detection of the breast cancer biomarker CA15-3 (Figure 21C). In this work, AuNPs on the g-C3N4 platform acted as a linker to

11-mercaptoundecanoic acid for the effective adsorption of antibodies. The performance of the PEC sensor was remarkable with a long linear range (0.1 fg/mL–10 ng/mL) and a very low detection limit (0.04 fg/mL). One of the promising candidates for immunosensor applications is 2D-Black phosphorus (BP) with high carrier mobility and controllable bandgap [171]. The unique properties of BP at atomic thickness are valuable for diverse applications [172–174]. Li et al. [175] reported a 2D-black phosphorous-supported Pt-Pd nanoelectrocatalyst for the determination of 4-AP, a potent biomarker for aniline exposure. Layered double hydroxides (LDHs) received attention because of their tunable chemistry and high charge density [176]. In one study, an electrochemical immunosensor based on AuNPs decorated ferrocene carboxylic acid conjugated MgAl layered double hydroxides for the label-free detection of CA-125 was reported by Wu et al. [177]. In this work, an LBL approach was used to increase the number of ferrocenes and antibodies, thereby amplifying the signal. The sensor reportedly displayed a wide linear range (0.01–1000 U/mL) and LOD (0.004 U/mL) and was tested for clinical cancer diagnostics (Figure 21D).

**Figure 21.** Schematic illustration of (**A**) Fabrication of a GDY-based self-powered device for miRNA-21 detection. Reprinted with permission from Ref. [164]. Copyright 2021 ACS, (**B**) Fabrication of AuNPs decorated boron nitride nanosheets based label-free aptasensor for the detection of the cardiac biomarker myoglobin. Reprinted with permission from Ref. [165]. Copyright 2019 Elsevier, (**C**) Graphitic carbon nitride sensitized with AuNPs for the PEC detection of CA15-3. Reprinted with permission from Ref. [170]. Copyright 2022 Elsevier, and (**D**) Fabrication of label-free electrochemical immunosensor based on LBL assembly of mesoporous carbon, AuNPs, and MgAl LDHs containing ferrocenecarboxylic acid. Reprinted with permission from Ref. [177]. Copyright 2022 Elsevier.


**Table 5.** Recent literature reports on biomarker detection based on various metal nanoparticles decorated 2D materials.
