**2.4 Composite nanobiosensors**

Another most commonly used material type is composite materials, in nanobiosensor applications. These materials have been developed with the combination of the desired properties of two or more materials in their structure, and these materials have also come to the fore in applications thanks to their superior properties [46]. So far, sensor studies have been reported on many nanomaterials-based biosensors that focused on flexible, stretchable, and wearable sensors to determine target analytes such as heart rate, blood pressure, breathing rate, serum electrolyte, temperature, creatinine, albumin, urea, DNA, RNA, and glucose. Based on the use of composite nanomaterials, Ebrahimi et al. developed a microRNA-199a-5p targeted electrochemical nanobiosensor for Triple-Negative Breast Cancer. The composite nanobiosensor was prepared using gold nanorods, GO, and graphene electrode glass. Fetal bovine serum and human serum samples were studied for detection of microRNA-199a-5p in this study. It was stated that high selectivity and sensitivity were observed in both sample environments. It has been reported that the prepared composite

#### *Nanostructures in Biosensors: Development and Applications DOI: http://dx.doi.org/10.5772/intechopen.108508*

nanobiosensor offers an important potential due to its detection even at low concentrations [47]. In another study, Karakuş et al. studied glucose detection by developing an electrochemical nanobiosensor prepared with polyacrylonitrile (PAN) and rGO. It has been stated that due to the redox mechanism provided by rGO, it allows glucose detection with high stability and sensitivity. It has been stated that compared with the PAN-based sensor, the nanobiosensor supplemented with rGO provides glucose detection with higher sensitivity [48]. This shows the importance of developing composite structures for nanobiosensor applications. In another study, Baytemir et al. studied the detection of glucose with an electrochemical nanobiosensor and developed a nickel phthalocyanine-borophene composite based nanobiosensor. It has been reported that the borophene-doped nanobiosensor exhibits high electrical conductivity and sensitivity compared with the NiPc nanobiosensor. It was also stated that the composite nanobiosensor exhibited a lower limit of detection value [49]. In another study, Samak et al. developed a novel nanobiosensor for H2S detection that is coupled with a DNA/sulfide fluorophore (SF) and a hybrid composite (alumina nanorods and GO nanosheet). In the study, it was stated that composite structures that can be produced in a controllable way are important in nanobiosensor applications and that the prepared composite nanobiosensor for sensitive and selective H2S detection in wastewater can be developed [50]. As seen from the literature, composite structures have an important potential for nanobiosensor applications and can be used in many different areas. In **Table 1**, comparison of developed nanobiosensor for the detection of specific analytes was presented.

#### **2.5 MXene nanobiosensors**

Discovered in 2011 and attracting great attention in recent years, especially in advanced nanosensor technologies, MXene is a 2D transition metal carbide and nitride material with different functional groups (-O, -OH, and -F). MXene sensors have been great attention with their excellent electrical, biological, chemical, surface, and mechanical properties in various applications such as water treatment systems, energy storage materials, photothermal systems, and sensor applications.

Recently, various types of 2D nanomaterials have been produced in small quantities for other applications outside the sensor field, whereas scale of production for healthcare applications poses a major challenge. In addition, it has been proven that most of the 2D materials produced have properties such as hydrophobic and instability in the air environment. Therefore, 2D MXene materials have a strong influence in the field of modern science, with the development of issues with superior metallic conductivity, ease of processing, hydrophilic character, chemical stability, and layered morphology. Soomro et al. developed a novel photo-electrochemical NiWO4- MXene sensor for the detection of the prostate-specific antigen [63]. According to the experimental results, it was found that the sensor had a wide detection range from 1.2 fg.mL−1 to 0.18 mg.mL−1 and a low detection limit of 0.15 fg.mL−1 for the prostate-specific antigen. In another study, Qin et al. reported that MXene/V2O5/ CuWO4-based sensor had a highly selective against ammonia at room temperature in few seconds [64]. Ranjbar et al. studied the sensing performance of the novel wearable conductive polymer/MXene-based pressure sensor for the human detection and information transmission using cotton fabric [65]. In another study, Zhu et al. developed a novel acetone sensor using ZnO/Ti3C2Tx-MXene composite nanomaterials [66]. The few-layered ZnO/Ti3C2Tx-MXene composite nanomaterial was prepared by a hydrothermal method Furthermore, the proposed nanosensor exhibited a


#### *Biosignal Processing*


**Table 1.**

*Comparison of developed nanobiosensor for the detection of specific analytes.*

*Nanostructures in Biosensors: Development and Applications DOI: http://dx.doi.org/10.5772/intechopen.108508*

*Biosignal Processing*

high-sensing response nearly six times higher than that of the ZnO in a concentration range of 14.4–100 ppm of acetone at 320°C due to the large specific surface area and layered structure. Finally, the sensing mechanism was proposed based on the large specific surface area, sufficient adsorption and reaction sites, a large number of oxygen functional groups (-O, -OH) of MXene nanostructures, and the surface of the modified electrode for sensing gas molecules.
