**3.3 Inorganic novel nanomaterials**

*Novel Nanomaterials*

of scientists.

[27–30].

**3.2 Gold nanostructures**

tion and catechol, respectively [28, 29].

cal diagnosis and treatment of tuberculosis [23].

There are studies in which GDY has been used in the preparation of electrochemical enzyme biosensors [21], for microRNA testing [22] and in the determination of bacterium [23]. GDY was investigated as matrix for tyrosinase (a model enzyme) immobilization to create a mediator-free GDY based biosensor for rapid detection of bisphenol A (BPA). In this study between different carbon nanomaterial based biosensors including carbon nanotube and graphene was compared and it was reported, GDY-based tyrosinase biosensor performed better analytical for BPA detection than CNTs and graphene-based biosensors [21]. A new photoactive material has been synthesized that integrates the properties of MoS2 and GDY to implement ultra-sensitive detection of microRNA [22]. Controllable synthesis of two-dimensional graphite nanosheet (GDY NS) is of great importance for the clini-

It is though that as a new promising 2D all-carbon nanomaterial after graphene, graphdiyne with intriguing properties would inevitably attract the general interest

Metal nanoparticles (NPs) such as gold and silver NPs have gained immense recognition in nanosensing and diagnostic applications [24, 25]. Therefore, ease of synthesis, versatile surface functionalization and long term stability of gold nano-

Gold nanostars modified with biotin were used for streptavidin determination [27]. Sensing applications using other shapes of gold nanomaterials include the use of gold nanowires and nanocubes for detection of bacteria in human kidney infec-

It has been reported that the nanosensor based on gold nanorodes is highly reproducible and has excellent selectivity. It was also reported the nanosensing platform is reliable, facile, cost-effective and less labor intensive. The nanomaterial with aspect ratio tunable property can be possibly used for several biomedical applications. **Figure 3** illusrates TEM and SEM images of some kind of gold nanosructures

*TEM (A,B) and SEM (C,D) images of gold nanostar (A) [27], gold nanorods (B) [28], gold nanoparticle (C)* 

Gold nanorods have also employed as a SERS substrate where in they have

materials increases their potential as efficient detection probes [26].

achieved highly sensitive and selective detection of DNA [30].

**176**

**Figure 3.**

*[29] and gold nanowire (D) [30].*

Recently, inorganic nanostructured materials have gained widespread attention as potential electrode materials of electrochemical sensors with excellent structural adjustability and other properties [31, 32].

In the past few years, binary metal oxides (denoted BMOs) are considered as one of the state-of-the-art electrocatalyst materials for various electrochemical applications [33, 34]. Among the different categories of BMOs, transition-metal phosphates/ phosphides (denoted TMPs) have attracted increasing attention as a promising electrocatalyst [35–37]. Ultrathin cobalt phosphate-based modified electrode was used for the non enzymatic electrochemical determination of glucose [38]. α-zirconium phosphate (α-ZrP) based electrocatalysts have been recognized as crucial for numerous electrochemical applications [39]. The sensitive electrochemical sensing probe using the ZrP nanoplates was successfully applied for Furazolidone detection [10].

**Figure 4** illustrates surface characterization of ZrP [10].

**Figure 4.** *(A*−*C) FEG-SEM image, (D*−*F) TEM images, (G) EDX spectrum, and (H*−*J) elemental mapping of ZrP.*

### **3.4 Nanozymes**

In the last decade, artificial nanomaterials, which exhibit properties similar to enzymes, have been shown as highly stable and low-cost alternatives to enzymes in electrochemical biosensing.

Nanozymes, combining the advantages of chemical catalysts and enzymes [40, 41], outperform natural enzymes because they are usually synthetized using low-cost, simple, and mass-production methods and offer high operational stability and self-life, robust catalytic performance [42–45]. Moreover, the smooth surface modification of nanomaterials provides more room for modifications than the natural enzymes. In addition, their inherent nanomaterial properties impart them both tunable and tenable catalytic activity [46, 47].

**Figure 5** illustrates the schematic presentation of the enzyme-based and nanozyme-based immunoassay.

**Figure 5.**

*Comparison of (A) natural enzyme-based immunoassays and (B) nanozyme-based immunoassays [46].*

The lack of selectivity of nanozymes is compensated for by using specific bioreceptors. However, it is important to be aware of the current lack of bio-ligands for emerging analytes and that their use compromises both stability and the low cost of nanozymes [48].

Affinity ligand-based electrochemical biosensors using nanozymes have been successfully developed and exhibit some excellent merits such as higher selectivity and sensitivity, lower cost, shorter detection time, and better signal readout [49].

Nanozymes, being a special type of nanomaterial, can be exploited in electrochemical affinity biosensing as electrode modifiers, nanocarriers, and/or catalytic labels. These multi functional nanozymes, which include PtNPs/CoTPP/rGO [49], Pd/APTES-MCeO2-GS [50], rGO-NR-Au@Pt [51], Mn3O4 and Pd@Pt nanoflowers [52], Fe3O4/PDDA/Au@Pt [53], MWCNTs/ GQDs [54, 55], and FeS2-AuNPs [56], have been decorated with detector antibody (Ab2) [49, 50], detector antibody (Ab2) + HRP [51, 54, 55], AuNPs + Ab2 [56], detector aptamer (Apt2) + HRP [47], or (Apt2) + HRP + G-quadruplex/hemin DNAzyme [46]. It is important to note that these nanozymes are often dressed with the natural enzyme to further enhance the sensitivity [51, 54, 55].

The combination of nanozyme-based electrochemical affinity biosensors with personalized equipment such as smartphones and/or portable low-cost devices will also be exciting to move forward in point-of-care testing. This nanozymes development to achieve catalytic activity and efficiency comparable or even better than natural enzymes will bring a revolution to conventional electrochemical biosensing and more practical applications in other expectation fields.

#### **3.5 Hybrid nanocomposites**

Hybrid sensing materials, which are organized by interaction of organic molecules onto inorganic supports, have been developed as a novel and hopeful class of hybrid sensing probes. Magnetic silica hybrid rather than other hybrid materials such as polymer, titania, and selfassembled monolayers [57–60] provides low toxicity, simple separation via external magnetic field, stability, biocompatibility and thermally stable advantages [61–63].

Biosensors prepared using hybrid materials were used to detect biological materials by thermal, electrical or optical signals. Examples of various applications of biosensors can be mentioned as environmental monitoring [64], forensic science [65–67], water characteristic testing [68], defense and the military [69], biomedicine, food industry and medical diagnosis [70].

**179**

*The Novel Nanomaterials Based Biosensors and Their Applications*

performed by transmission electron microscopy (TEM) [57].

*TEM images of Fe3O4@ SiO2 NPs with Fe3O4 sizes of (a) 8.8 nm and (b*−*d) 12.2 nm.*

Magnetic silica hybrids were reported as fluorescent, colorimetric, electrochemical and Surface-enhanced raman spectroscopy (SERS) sensing probes [71]. Inorganic mesoporous material is one of the best materials as molecular catalysts due to its thermal stability, easy production and modification. It used in the fields of biomedicine, electronics, and physicochemistry. Silica-coated Fe3O4 nanoparticle (Fe3O4@SiO2 NPs), have good excellent conductivity, electrochemical transducers, biocompatibility, catalytic activity, separation ability and low toxicity properties to produce "electronic wires" to increase the electron transfer between redox centers

**Figure 6** illustrates the surface characterization of Fe3O4@ SiO2 nanoparticles

DNA nanomaterials have been widely used in bioassays due to their promising properties for sensitive and specific detection of biomolecules. The electrochemical biosensor has received greater attention in clinical diagnosis due to its high sensitivity, easy controllability and low cost [72]. For this reason, the biomolecular recognition and signal amplification based on electrochemical platform to achieve miRNAs

In recent years, legion nucleic acid nanostructures have been applied to biological detection, including DNA tetrahedron, DNA gels, DNA dendrimers, and so on [73–75]. Y-shaped DNA (Y-DNA), as a constant nanostructure with high selectivity, provides an effective method for completely measuring target molecules [76]. Y-DNA consists of three oligonucleotides that are partially hybridized to each other. Some older biosensors used this feature to perform DNA detections where one DNA stand is fixed to the surface, another DNA stand and target DNA are added to form a specific structure [77]. Numbers of signal amplification strategies have been developed, including hybridization chain reaction (HCR), strand displacement amplification (SDA), catalytic hairpin assembly (CHA) and rolling circle amplification (RCA) [78–81]. The HCR consists of a trigger sequence and two partially complementary hairpin probes. Once triggered, the two hairpin probes can autonomously hybridize continuously [82].

*DOI: http://dx.doi.org/10.5772/intechopen.94930*

and electrode surfaces in proteins [72].

**3.6 DNA nanomaterials**

**Figure 6.**

detection still need to be considered.

*The Novel Nanomaterials Based Biosensors and Their Applications DOI: http://dx.doi.org/10.5772/intechopen.94930*

*Novel Nanomaterials*

nanozymes [48].

**Figure 5.**

sensitivity [51, 54, 55].

**3.5 Hybrid nanocomposites**

thermally stable advantages [61–63].

The lack of selectivity of nanozymes is compensated for by using specific bioreceptors. However, it is important to be aware of the current lack of bio-ligands for emerging analytes and that their use compromises both stability and the low cost of

*Comparison of (A) natural enzyme-based immunoassays and (B) nanozyme-based immunoassays [46].*

Affinity ligand-based electrochemical biosensors using nanozymes have been successfully developed and exhibit some excellent merits such as higher selectivity and sensitivity, lower cost, shorter detection time, and better signal readout [49]. Nanozymes, being a special type of nanomaterial, can be exploited in electrochemical affinity biosensing as electrode modifiers, nanocarriers, and/or catalytic labels. These multi functional nanozymes, which include PtNPs/CoTPP/rGO [49], Pd/APTES-MCeO2-GS [50], rGO-NR-Au@Pt [51], Mn3O4 and Pd@Pt nanoflowers [52], Fe3O4/PDDA/Au@Pt [53], MWCNTs/ GQDs [54, 55], and FeS2-AuNPs [56], have been decorated with detector antibody (Ab2) [49, 50], detector antibody (Ab2) + HRP [51, 54, 55], AuNPs + Ab2 [56], detector aptamer (Apt2) + HRP [47], or (Apt2) + HRP + G-quadruplex/hemin DNAzyme [46]. It is important to note that these nanozymes are often dressed with the natural enzyme to further enhance the

The combination of nanozyme-based electrochemical affinity biosensors with personalized equipment such as smartphones and/or portable low-cost devices will also be exciting to move forward in point-of-care testing. This nanozymes development to achieve catalytic activity and efficiency comparable or even better than natural enzymes will bring a revolution to conventional electrochemical biosensing

Hybrid sensing materials, which are organized by interaction of organic molecules onto inorganic supports, have been developed as a novel and hopeful class of hybrid sensing probes. Magnetic silica hybrid rather than other hybrid materials such as polymer, titania, and selfassembled monolayers [57–60] provides low toxicity, simple separation via external magnetic field, stability, biocompatibility and

Biosensors prepared using hybrid materials were used to detect biological materials by thermal, electrical or optical signals. Examples of various applications of biosensors can be mentioned as environmental monitoring [64], forensic science [65–67], water characteristic testing [68], defense and the military [69],

and more practical applications in other expectation fields.

biomedicine, food industry and medical diagnosis [70].

**178**

Magnetic silica hybrids were reported as fluorescent, colorimetric, electrochemical and Surface-enhanced raman spectroscopy (SERS) sensing probes [71]. Inorganic mesoporous material is one of the best materials as molecular catalysts due to its thermal stability, easy production and modification. It used in the fields of biomedicine, electronics, and physicochemistry. Silica-coated Fe3O4 nanoparticle (Fe3O4@SiO2 NPs), have good excellent conductivity, electrochemical transducers, biocompatibility, catalytic activity, separation ability and low toxicity properties to produce "electronic wires" to increase the electron transfer between redox centers and electrode surfaces in proteins [72].

**Figure 6** illustrates the surface characterization of Fe3O4@ SiO2 nanoparticles performed by transmission electron microscopy (TEM) [57].

**Figure 6.** *TEM images of Fe3O4@ SiO2 NPs with Fe3O4 sizes of (a) 8.8 nm and (b*−*d) 12.2 nm.*

#### **3.6 DNA nanomaterials**

DNA nanomaterials have been widely used in bioassays due to their promising properties for sensitive and specific detection of biomolecules. The electrochemical biosensor has received greater attention in clinical diagnosis due to its high sensitivity, easy controllability and low cost [72]. For this reason, the biomolecular recognition and signal amplification based on electrochemical platform to achieve miRNAs detection still need to be considered.

In recent years, legion nucleic acid nanostructures have been applied to biological detection, including DNA tetrahedron, DNA gels, DNA dendrimers, and so on [73–75]. Y-shaped DNA (Y-DNA), as a constant nanostructure with high selectivity, provides an effective method for completely measuring target molecules [76]. Y-DNA consists of three oligonucleotides that are partially hybridized to each other. Some older biosensors used this feature to perform DNA detections where one DNA stand is fixed to the surface, another DNA stand and target DNA are added to form a specific structure [77].

Numbers of signal amplification strategies have been developed, including hybridization chain reaction (HCR), strand displacement amplification (SDA), catalytic hairpin assembly (CHA) and rolling circle amplification (RCA) [78–81]. The HCR consists of a trigger sequence and two partially complementary hairpin probes. Once triggered, the two hairpin probes can autonomously hybridize continuously [82].

Compared to HCR, this reaction consists of more complex components, including a trigger sequence, two double stranded substrates with bridging loops in the middle, and two helper sequences [83]. Thus, non-linear HCR can achieve higher rates of amplification and molecular weights [84].

To join non-linear HCR and Y-DNA nanostructures, the Y-DNA's terminals were designed as triggers that could initiate the amplification reaction. As a result, the new biosensing method can provide high-precision and selective detection of biological molecules. An unlabeled DNA nanostructured electrochemical biosensor was designed to detect miRNA-25, which is reported to be a potential molecular biomarker for non-small cell lung cancer and heart failure [85, 86].

Expanding the application of DNA nanomaterials to bioassays in the future may enable early and effective detection of various diseases.

#### **3.7 DNAzyme**

DNAzymes are single-stranded (ss) DNA sequences are able to catalyze a number of reactions, including cleavage of the phosphodiester backbone at a ribonucleotide or deoxyribonucleotide site [87]. It has been shown that metal ions play an important role in the catalytic process and are essential for the catalytic activity of most known DNAzymes [88].

The ability to select a DNAzyme with metal ion specific activity without previous chemical knowledge of the DNAzyme structure, and then to subsequently modify DNAzyme binding arms and other insignificant nucleotides with minimal to no effect on sensitivity and selectivity has made DNAzymes ideal metal-selective components for new metal ion sensing technologies. RNA-cleaving DNAzyme is a very useful biomaterial for the determination of metal ions, but some parts of DNAzymes can be cleaved by several metal ions, which makes different concentrations of metal ions difficult to distinguish [89].

In the last two decades, the rapid development of nanomaterials and biomaterials [90] offers more opportunities to improve electrochemical sensor performance. For the determination of Cu (II) and Hg (II), many highly sensitive sensors are manufactured using small molecules, peptides, proteins and antibodies at low cost.

The ligand sites of proteases composed of nitrogen, oxygen or sulfur can combine with heavy metal ions to form a stable complex [91]. Cu(II) is a small ion that has to be chelated first and then bind to the antibody recognition [92]. Both antibody and enzyme work best under physiological conditions that limit application in real environment. DNA is not only the genetic material of most living organisms, but also an excellent biological functional material [93].

Metal ions can be specifically bound with a single-stranded DNA to form a stable metal-mediated DNA, and this mechanism is applied to detect metal ions [94, 95]. Therefore, numerous studies have focused on the newly discovered biosensor using different DNA-based aptamers functionalized with nanomaterials to increase sensitivity. DNAzymes that break down RNA as DNA-based catalysts are obtained through in vitro selection, which turned out to be a very useful platform for the identification of metal ions. After binding with heavy metal ions, many biochemical and biophysical studies have been conducted on DNAzymes due to their high metal ion selectivity and high catalytic efficiency [96]. Therefore, DNAzymes have been applied in various biosensors (colorimetric, electrochemical and fluorescent) that realize the detection of various metal ions such as Mg(II) [97], Ag(I) [98], Pb(II) [99], Zn(II) [100], Hg(II) [101], UO2(II) [102].

The field of DNAzyme-based metal ion sensing is continuing to develop for future cellular and portable detection technologies.

**181**

**Figure 7.**

*The Novel Nanomaterials Based Biosensors and Their Applications*

Carbon dots (CDs) are nanomaterials less than 10 nm in size and became the new potential material for the electrode modifier [103]. Formerly, CDs have been applied in electrochemical sensing platforms, mainly focusing on their electrocatalytic properties toward analytes of interest [104, 105] rather than electrode modifiers. Thus, the studies on carbon dots owing a noticeable potential to be used as electrode modifiers in electrochemical techniques to increase the sensitivity of the

Recently, a new member of CDs, have gained attention because of their water solubility, fine properties, high luminescence, low cytotoxicity and good conductivity [106]. Depending on the precursors employed in their synthesis, CNDs are surrounded by different functional groups including, among others, hydroxyl, amide groups and carboxyl which facilitate the immobilization of biomolecules. Hence, due to their ability to be modified with a wide variety of biomolecules, and in conjunction with the excellent properties mentioned above, CNDs have been employed in many biological applications such as solar cell development and photocatalysis [107, 108]. Concerning the employment of CNDs for electrochemical biosensors, it should be highlighted that despite the previously mentioned advantages, very few attempts to incorporate CNDs into electrodes are reported. Reporting the application of CNDs in electrochemical sensors are focused on the electrocatalytic properties of this nanomaterial toward oxygen reduction [109], biomedical application

Transmission electron microscopy (TEM) of carbon nanodots in different scale

Since the discovery of carbon nanotubes, carbon-based nanomaterials being researched in various disciplines including electrochemistry. An old and cost-effective material recently called carbon black (CB) reinvented. CB has good electrical conductivity, dispersible in solvents, possibility of easy functionalization and has a

Previously, CB's main application in the electrochemical field was based on the design of sensors for analyte detection in fuel cell and gas phases for lithium and sodium batteries [117, 118]. However, until 2009, only a few CB-based electrochemi-

Among nanomaterials, CB demonstrated high potential in customizing all from

the oldest carbon paste to glassy carbon and printed electrodes thanks to their fascinating electrochemical properties combined with cost effectiveness**.**

large number of defect areas and fast electron transfer kinetics [113–116].

*High resolution transmission electron microscopic images of fish scale derived carbon nanodots (a-c).*

[110], exploited for glucose biosensing [111] and DNA sensing [112].

from 20 nm to 2 nm are illustrate in **Figure 7** [110].

**3.9 Carbon black nanomaterials**

cal sensors were reported for analyte detection.

*DOI: http://dx.doi.org/10.5772/intechopen.94930*

electrochemical sensor has been exploited.

**3.8 Carbon nanodots**
