highly sensitive target detection (Figure 17.4b). The carbon nanodot (CND) is another

example of the carbon-based nanomaterials applicable in biological fields. The CND is a

spherical NP less than 10 nm in size, usually in the form of nanocrystals with sp²/sp³

carbon clusters. The CND has merits for the fabrication of bioelectronic devices such as

electrical conductivity, high solubility in various solvents, and large active areas. By using

the CND, Ramadan’s group fabricated a CND-based FET biosensor for ultrasensitive

detection of exosomes [24]. In this research, the CND was introduced to promote the

capturing efficiency of exosomes and increase the sensitivity of the FET biosensor. In

addition, various types of carbon-based nanomaterials such as the multi-well carbon

nanotubes (MWCNTs), crumpled graphene, and graphene quantum dots (GQDs) have

been reported to be used in biological fields [25], particularly in the development of

bioelectronic devices.

17.3.3 TMD Nanomaterials

Recently, TMD nanomaterials including molybdenum disulfide (MoS2), tungsten dis­

elenide (WSe2), molybdenum diselenide (MoSe2), and tungsten disulfide (WS2) have re­

ceived intensive attention due to the fascinating physicochemical and electrochemical

properties resulting from quantum size effects in ultrathin-layered structures [26]. The

TMD nanomaterials are classified into 2H phase and 1T phase, according to the crystal

structure, and each has unique properties. The 2H phase of TMD nanomaterials shows

excellent catalytic, electronic performance, and semiconducting characteristics for energy-

related applications including super-capacitor and battery. The 1T phase of TMD nano­

materials generally has metallic properties such as enhancement of charge transfer

efficiency and electrochemical performance. Also, the TMD nanomaterials have a direct

bandgap that enables them to overcome the bandgap problem of graphene. Accordingly,

TMD nanomaterials are used to develop bioelectronic devices such as FET, biomemory,

and biosensors. As shown in Figure 17.4c, Kim’s group reported a bioelectronic platform

using the MoS2 nanosheets for FET based ion channel activity monitoring [21]. For this,

the liquid-gated MoS2 FET array was fabricated, and the developed device detected the

changes in electrolytes through changes in the electrical properties of MoS2 nanosheets. The

electrical properties of MoS2 nanosheets were affected by proton transport through the lipid

bilayer on the surface of the MoS2 nanosheets. In another study, Kim’s group developed a

soft bioelectronic device using high-density MoS2-graphene heterostructure [27]. Here, an

atomically thin MoS2-graphene heterostructure was developed as a phototransistor, which

had two to three times higher photosensitivity compared to a silicon photodiode of the

same thickness, due to the efficient photo-absorption of MoS2. As briefly discussed here,

MoS2 nanosheets are studied the most, but WSe2, WS2, and other structures of MoS2

(quantum dot (QD), NR) are also being gradually studied to combine with biomaterials for

developing bioelectronic devices [28].

17.3.4 Mxene Nanomaterials

Since the discovery of graphene, 2D nanomaterials have received a lot of attention for

applications in various fields due to their high anisotropy and chemical function. In par­

ticular, 2D transition metal carbides (or nitrides) named MXene have been studied [29].

The MXene consists of Mn+1XnTx, and in that composition, M is a transition metal (e.g., Ti,

V), X is carbon and nitrogen, and Tx is a functional group (e.g., -F, -OH). The MXene exhibits

high dispersibility in an aqueous solution because it has a layered structure and a

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