15.4 Classes of Bioanalytical Sensors Based on MXenes

15.4.1 Bioelectronics

In recent years, two-dimensional MXenes have gained much attention owing to their

excellent electrical properties and good mechanical stability and hence they have been

utilized in biomedical applications. MXenes exhibit excellent qualities for fabricating

bioelectronics devices; however, self-restacking and agglomeration reduce their specific

surface area and stability, limiting their use in biomedical applications [33]. The most

effective technique to address such challenges is to transform 2D MXenes into 3D

MXenes. It has been found that converting accordion-like Ti3C2 MXene into urchin-like

sodium titanate (M-NTO) via oxidation and alkalization efficiently prevents MXene self-

stacking. However, the produced M-NTO tends to impair conductivity due to the wide

bandgap of sodium titanate (3.7 eV), and such problems could be efficiently managed by

inserting additional conductive materials into M-NTO. Because of their superior electrical

conductivity, ease of manufacture, and light weight, CPs are explored extensively among

various conductive materials and/or polymers [34]. PEDOT was an obvious candidate for

bioelectronics due to its superior stability, biocompatibility, and electrochemical catalytic

activity [34]. Incorporating conductive PEDOT with advanced nanomaterials could pro­

duce synergistic effects, improve electrochemical sensitivity, and keep the morphologies

of the base substrates intact. Because of all of these factors, PEDOT is an excellent option

for incorporating M-NTO to enhance electrical conductivity. These materials (M-NTOP­

EDOT) generate a huge surface area possessing quick transportation of electrons that

could be exploited to make biomedical gadgets [34]. For example, Xu et al. [35] described

label-free immunosensors based on gold nanoparticles (AuNPs) and M-NTO-PEDOT

to detect prostate-specific antigen (AuNPs/M-NTO-PEDOT) (PSA). The oxidation and

alkalization of HFetched Ti3C2 MXene nanosheets, followed by in situ oxidation to in­

tegrate PEDOT with M-NTO, were used to make macroporous M-NTO in this study.

They also added AuNPs to the surface of M-NTO-PEDOT to increase the number of

binding sites for PSA antibodies. Hence, AuNPs/MNTO-PEDOT combination, which

possesses a huge surface area and good electrical conductivity, allowed the modified

electrode to load substantial amounts of PSA antibodies and transmit charge quickly. The

immunosensor’s advantages included increased electrochemical test sensitivity and

signal amplification. PSA was injected into human serum samples and detected within an

acceptable range of 96.13% to 107.1% by the immunosensor.

15.4.2 Enzyme Sensors

The creation of electrochemical biosensors requires direct electron transfer of electrons

directly among enzymes and electrodes. MXene has a variety of unique features, in­

cluding a higher specific surface area and excellent electrical conductivity; hence, its

addition could be an effective means of facilitating direct electron transfer. It is worth

mentioning that, for the first time, Ti3C2 has been used in the construction of an elec­

trochemical sensor towards hydrogen peroxide as a MXene [36]. Moreover, encapsulation

of enzyme hemoglobin, which directly correlates to the protein to keep it stable and active

has been done by using Ti3C2. Additionally, for mediator-free enzyme-based sensors,

Ti3C2 MXenes were suitable candidates for direct electron transfer of hemoglobin. Other

enzymes such as tyrosinase and acetylcholinesterase were also immobilized onto the

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Bioelectronics