**1. Introduction**

Polymer nanocomposites (PNCs) have electrochemical properties as transducers which can be used for the manufacturing of electrochemical sensors and biosensors. They possess significant variations in responsiveness, synthesis, and morphology, which help in a significant level of variations in conductivity [1]. Afar from the economic aspect of the PNC-based sensors, the improved performance on the electronic side stands apart among its peers through the basal plane ratio of the nanofillers, method of doping, kinetic properties of the electrode, biological response and environmental impact [1]. The impact of nanofillers in PNCs plays a significant role in sensing, processing, and actuating capabilities of the electrodes of electrochemical and biosensing applications [2].

The "active states of PNCs" rests on three pillars: high electrical conductivity rate, large surface area and fast electron rate which leads to best electricidal sensor outcomes. PNCs helps in the material technological advancement of electrochemical sensors which have high sensitivity and selectivity, lower detection limits, reproducibility and stability as shown in **Figure 1**. All these increased used the PNCs in electrochemical sensor research which were manufactured through chemical synthesis or polymerization methods and could be easily scaled up for

**Figure 1.**

*Key properties of PNC based electrochemical sensors and biosensors. With permission from Elsevier [1].*

various applications [3]. The electrochemical sensors along with the immunosensors and biosensors are becoming the norm of the day. Detections limits and sensing technologies are improved consistently due to developments happening in the unique properties of PNCs especially conductivity and electrochemical activity. The interactive fillers facilitate ion diffusion that impacts the sensing applications through intercalation into the PNC matrices leading to better stability of active electron transfer sites and detection limits. These active fillers help in reducing the layer thickness in PNC leading to ultrathin electrochemical detector technology. PNCs stand as an outstanding leader with significant advantages in large specific interaction surface area, reduced dimension of fillers and efficient electron transfer rate [3].

## **2. Electrochemical sensors**

PNCs are widely used in the development of electrochemical sensors. The electrochemical sensors are based on three categories of PNCs. PNCs of conductive polymers and inorganic nanomaterials, PNCs of conductive polymers and Grp, and PNCs of conductive polymers and CNTs. Once interaction has occurred between the PNC-based electrochemical sensors and the target analyte, an electronic signal is detected by the transduction system. The applications of PNC-based electrochemical sensors different materials are shown in **Table 1**.

#### **2.1 Polymer nanocomposites based on conductive polymers and inorganic nanomaterials**

Metal and metal oxide nanoparticles have been extensively studied as electrochemical sensing materials due to such beneficial features as their small size; unique chemical, physical, and electronic properties; flexibility in fabricating novel and improved sensing devices; and good sensitivity to the ambient conditions are shown in **Table 1**. The assimilation of nanoparticles of metals into PNC matrices set the stage for enhanced electrocatalytic electrode detection leading to multiple modernday applications. For example, a Zinc oxide nanoparticle intercalated into polypyrrole (ZnO-PPy) PNC showed excellent Xanthine detection by through xanthine oxidase enzyme immobilization [4]. A glassy carbon electrode (GCE) modified with ultrathin polypyrrole nanosheets decorated with Ag nanoparticles was fabricated for the detection of hydrogen peroxide (H2O2). The modified device showed

**161**

11.4 μA mM<sup>−</sup><sup>1</sup>

**Table 1.**

sensitivity of 604.2 μAmM<sup>−</sup><sup>1</sup>

*Polymer Nanocomposite-Based Electrochemical Sensors and Biosensors*

**Sensory material Analyte Detection limit** PPy-ZnO-Pt Xanthine 0.8 μM PPy-Pt-GCE Hydrogen peroxide 0.6 μM PANI-TiO2-GCE Glucose 0.5 μM PANI-NiCo2O4-GCE Glucose 0.3833 μM PANI-Grp-GCE 4-aminophenol 6.5 × 10<sup>−</sup><sup>8</sup>

PANI-Grp-ITO Artesunate 0.012 ng mL<sup>−</sup><sup>1</sup> PANI-Grp-GCE Lercanidipine 1.94 ng mL<sup>−</sup><sup>1</sup> PANI-Grp-GCE Nitazoxanide 2.2 μg mL<sup>−</sup><sup>1</sup> PPy-Grp-GCE Adenine 0.02 μM

PPy-PIL-GO-GCE Dopamine 73.3 nM PEDOT-rGO-GCE Dopamine 39.0 nM PEDOT-Grp-GCE Ascorbic acid 2.0 μM PANI-Grp-Bi2O3-GCE Etodolac 10.03 ng mL<sup>−</sup><sup>1</sup> PANI-rGO-MIP-AuNP-GCE Serotonin 11.7 nmol L<sup>−</sup><sup>1</sup> PPy-MWCNT-ITO Cholesterol 0.04 mM L<sup>−</sup><sup>1</sup> PPy-MWCNT-GCE Pemetrexed 3.28 × 10<sup>−</sup><sup>9</sup>

high sensitivity toward the reduction of H2O2 [5]. Similar electrochemical sensor based on polypyrrole–platinum (PPy-Pt) PNC was fabricated for the detection of H2O2 [6]. Another voltammetric sensor based on a polyaniline-gold nanoparticle (PANI-AuNP) PNC deposited on GCE was used for the detection of epinephrine (EP) and uric acid (UA) [6]. Exploiting the advantages of PNCs, two GCEs modified with PANI-TiO2 and PANI-NiCo2O4 PNC-based electrochemical sensors were developed for the detection of glucose [7]. TiO2 nanotubes (TNTs) was intercalated into a PANI-TNT PNC composite for through hydrothermal method for the detec-

PEDOT-CNT-CPE Hydroquinone 0.3 μM PEDOT-CNT-CPE Dopamine 20.0 nM PEDOT-CNT-CPE Nitrobenzene 83.0 nM

) by the immobilization of glucose oxidase (GOD) [7].

Graphene (Grp), an allotrope of carbon, has become the new material of interest

**2.2 Polymer nanocomposites based on conductive polymers and graphene**

and widely integrated into the sensor research from the beginning of this millennium due to its unique properties of electrical conduction and 2-dimensional existence. Grp-PNC-based electrochemical sensors are used for electroanalytical detection of target molecules with high precision of selectivity and sensitivity as shown in **Table 1**, which showed spectacular detection limits over a wide range. An electrochemical sensor fabricated for the detection of 4-aminophenol (4-AP) using

a PANI-Grp-GCE-modified device showed a detection limit of 6.5 × 10<sup>−</sup><sup>8</sup>

PNC onto an ITO plate with immobilized horseradish peroxidase enzyme with a

) of glucose (a reported sensitivity of

Guanine 0.01 μM

[8]. A sensor was fabricated with a PANI-Grp-based

M and

M

M

tion (a reported sensitivity of 11.4 μA mM<sup>−</sup><sup>1</sup>

*Electrochemical sensors based on polymer nanocomposites [1].*

*DOI: http://dx.doi.org/10.5772/intechopen.86826*


*Polymer Nanocomposite-Based Electrochemical Sensors and Biosensors DOI: http://dx.doi.org/10.5772/intechopen.86826*

#### **Table 1.**

*Nanorods and Nanocomposites*

various applications [3]. The electrochemical sensors along with the immunosensors and biosensors are becoming the norm of the day. Detections limits and sensing technologies are improved consistently due to developments happening in the unique properties of PNCs especially conductivity and electrochemical activity. The interactive fillers facilitate ion diffusion that impacts the sensing applications through intercalation into the PNC matrices leading to better stability of active electron transfer sites and detection limits. These active fillers help in reducing the layer thickness in PNC leading to ultrathin electrochemical detector technology. PNCs stand as an outstanding leader with significant advantages in large specific interaction surface area, reduced dimension of fillers and efficient electron transfer

*Key properties of PNC based electrochemical sensors and biosensors. With permission from Elsevier [1].*

PNCs are widely used in the development of electrochemical sensors. The electrochemical sensors are based on three categories of PNCs. PNCs of conductive polymers and inorganic nanomaterials, PNCs of conductive polymers and Grp, and PNCs of conductive polymers and CNTs. Once interaction has occurred between the PNC-based electrochemical sensors and the target analyte, an electronic signal is detected by the transduction system. The applications of PNC-based electro-

**2.1 Polymer nanocomposites based on conductive polymers and inorganic** 

Metal and metal oxide nanoparticles have been extensively studied as electrochemical sensing materials due to such beneficial features as their small size; unique chemical, physical, and electronic properties; flexibility in fabricating novel and improved sensing devices; and good sensitivity to the ambient conditions are shown in **Table 1**. The assimilation of nanoparticles of metals into PNC matrices set the stage for enhanced electrocatalytic electrode detection leading to multiple modernday applications. For example, a Zinc oxide nanoparticle intercalated into polypyrrole (ZnO-PPy) PNC showed excellent Xanthine detection by through xanthine oxidase enzyme immobilization [4]. A glassy carbon electrode (GCE) modified with ultrathin polypyrrole nanosheets decorated with Ag nanoparticles was fabricated for the detection of hydrogen peroxide (H2O2). The modified device showed

chemical sensors different materials are shown in **Table 1**.

**160**

rate [3].

**Figure 1.**

**2. Electrochemical sensors**

**nanomaterials**

*Electrochemical sensors based on polymer nanocomposites [1].*

high sensitivity toward the reduction of H2O2 [5]. Similar electrochemical sensor based on polypyrrole–platinum (PPy-Pt) PNC was fabricated for the detection of H2O2 [6]. Another voltammetric sensor based on a polyaniline-gold nanoparticle (PANI-AuNP) PNC deposited on GCE was used for the detection of epinephrine (EP) and uric acid (UA) [6]. Exploiting the advantages of PNCs, two GCEs modified with PANI-TiO2 and PANI-NiCo2O4 PNC-based electrochemical sensors were developed for the detection of glucose [7]. TiO2 nanotubes (TNTs) was intercalated into a PANI-TNT PNC composite for through hydrothermal method for the detection (a reported sensitivity of 11.4 μA mM<sup>−</sup><sup>1</sup> ) of glucose (a reported sensitivity of 11.4 μA mM<sup>−</sup><sup>1</sup> ) by the immobilization of glucose oxidase (GOD) [7].

PEDOT-CNT-CPE Nitrobenzene 83.0 nM

### **2.2 Polymer nanocomposites based on conductive polymers and graphene**

Graphene (Grp), an allotrope of carbon, has become the new material of interest and widely integrated into the sensor research from the beginning of this millennium due to its unique properties of electrical conduction and 2-dimensional existence. Grp-PNC-based electrochemical sensors are used for electroanalytical detection of target molecules with high precision of selectivity and sensitivity as shown in **Table 1**, which showed spectacular detection limits over a wide range. An electrochemical sensor fabricated for the detection of 4-aminophenol (4-AP) using a PANI-Grp-GCE-modified device showed a detection limit of 6.5 × 10<sup>−</sup><sup>8</sup> M and sensitivity of 604.2 μAmM<sup>−</sup><sup>1</sup> [8]. A sensor was fabricated with a PANI-Grp-based PNC onto an ITO plate with immobilized horseradish peroxidase enzyme with a

sensitivity limit of 0.15 mA ng mL<sup>−</sup><sup>1</sup> [9]. A PANI-Grp-GCE-based PNC sensor for the elimination of calcium antagonist lercanidipine in pharmaceutical formulations for medical purposes showed a detection limit in the range from 5 to 125 ng mL<sup>−</sup><sup>1</sup> [10]. The same PANI-Grp-GCE-based PNC sensor showed the detection of nitazoxanide compound which was an added advantage [11]. Electrochemical sensors based on PPy-based PNC are becoming popular these days due to their specific applications through their overoxidized form polypyrrole (PPyox). Fabrication of polypyrrole-graphene (PPyox/Grp) helped in the simultaneous detection of adenine and guanine through an electrodeposition method. PPy-Grp composite was electro-polymerized with pyrrole and graphene oxide (GO), followed by electrochemical reduction of GO composite. The electrochemical sensor's significant improvement in the sensing of adenine and guanine is due to the specific structure of the nanocomposite. The adenine and guanine showed strong π-π interactions, and cationic selectivity [12].

The detection of Dopamine (DA) using PNCs was the holy grail in neurochemical studies ad it is a prominent neurotransmitter, which plays a role in neurological disorders such as Parkinson's disease and schizophrenia [13]. A poly(ionic liquid)-functionalized polypyrrole-graphene oxide (PIL-PPy-GO)-based PNC electrochemical sensor was fabricated by the polymerization of 1-vinyl-3-ethylimidazolium bromide on N-vinyl imidazolium-modified PPy-GO films. The PILs helped in changing the surface charge which dispersibility of the PIL-PPy-GO composite and helped in the detection of DA [14]. Another sensor used for the detection of DA was a PNC-based poly (3,4-ethylene dioxythiophene)-graphene oxide (PEDOT-GO) fabricated by electrodeposition showed significant sensing capabilities [15]. A one-step electrochemical redox synthesis process of PEDOT-Grp PNC film was done using simultaneous electrodeposition of PEDOT and electrochemical reduction of GO on a GCE with high detection sensing of the ascorbic acid molecules. In this sensor PEDOT-Grp thin film PNC mediated the electron transfer between AO and electrode interface resulting in significant improvement in electrocatalytic activity and sensitivity of ascorbic acid molecules [16]. Jain et al. [5] introduced the combination of Grp and a conducting PANI-Bi2O3 PNC, the synergic effect of which enhanced the performance of sensors used for the electrocatalytic oxidation of etodolac in pharmaceutical formulations.

In recent years, molecularly imprinted polymers (MIPs) with high selectivity, affinity, chemical stability, and easy preparation for the template molecule are a promising candidate for developing a new generation of recognition elements for sensors. A double-layered membrane-sensing interface was fabricated based on rGO-PANI nanocomposites and MIPs embedded with AuNPs for sensitive and selective detection of serotonin (5-hydroxytryptamine, 5-HT). The obtained sensor showed remarkable selectivity to serotonin against the interferences caused by ascorbic acid and other interferents with a good detection limit of 11.7 nmol L<sup>−</sup><sup>1</sup> [17].

#### **2.3 Polymer nanocomposites based on conductive polymers and carbon nanotubes**

PNCs based on conductive polymers helped in improving the sensing properties of the electrochemical sensors with enhanced selectivity and stability. Some of the popular CNT-based PNC reported in the literature are shown in **Table 1**. A PPymultiwalled carbon nanotube (MWCNT)-toluene sulfonic acid-based PNC was fabricated fr the detection of cholesterol with ITO-coated glass was the substrate for the sensor. The sensor showed high sensitivity and a fast response time of 9 s [18]. Sodium dodecyl sulfate-doped PPyox) with carboxylic acid functionalized MWCNT-modified GCE were reported for the detection of the anticancer drug

**163**

**Table 2.**

*Polymer Nanocomposite-Based Electrochemical Sensors and Biosensors*

ies is summarized in **Table 2** and discussed in the section below.

fabricated with PANI–AuNP PNC was used for the detection of Ag+

from the cytosine to Ag+

mol L<sup>−</sup><sup>1</sup>

The schematic illustration of the most popular DNA biosensor based on polyaniline-gold nanoparticle-chitosan-graphene sheet (PANI-AuNP-Cts-GS) composite with a functional capture probe for the detection of BCR/ABL fusion gene in chronic myelogenous leukemia (CML) is shown in **Figure 2**. The capture probe used a hairpin structure and was dually labeled with a 5′-SH and a 3′-biotin. The biotin electrode probe was used for the detection of streptavidin–alkaline phosphatase (AP) enzyme which in turn cause an electrochemical signal caused by the catalytic reduction of 1-naphthyl phosphate to 1-naphthol picked up by Diffuse Pulse Voltammetry (DPV) with a detection range of 10–1000 pM [21]. A DNA biosensor

the following principle: the electrochemical biosensor regenerates cysteine leading

The fabricated biosensor showed excellent selectivity with a good detection limit for silver ions [22]. Another DNA electrochemical biosensor was developed using polyaniline nanofibers (PANI-nf) enrapturing AuNPs making (PANI-nf-AuNP), a PNC. Gold was used as the electrode for the detection of *Staphylococcus aureus* DNA from the PANI-nf-AuNPs sensor, where the detection concentration varied

Fe3O4-CNT PNC was manufactured for sensing *Neisseria gonorrhoeae* through a DNA probe. The fabricated biosensor showed sensing in the range from 1 × 10<sup>−</sup><sup>19</sup>

**Sensor Analyte Detection limit** PANI-AuNP-GS-Cts-GCE BCR/ABL fusion gene 2.11 pM PANI-AuNP-Au Silver ions 10 pM PANI-AuNP-Au DNA sequence associated with *S. aureus* 150 pM–1 μM PPy-PANI-AuNP-Au 15-mer DNA oligonucleotides 1.0 × 10<sup>−</sup>13 M PPy-PEDOT-AgNP-GCE 27-mer DNA oligonucleotides 5.4 ± 0.3 × 10<sup>−</sup>15 M PANI-Fe3O4-CNT-ITO *Neisseria gonorrhoeae* 1 × 10<sup>−</sup>19 M PANI-AuNP-GSPE microRNA-16 0.1 nM

. It works on


[23]. A DNA biosensor based on the PANI-

pemetrexed (PMX). The results showed that overoxidation of the PPy film conferred a negative charge density on the porous layer, which in turn enhances the adsorption of PMX [19]. Xu et al. fabricated a carbon paste electrode (CPE) modified with a PEDOT-CNT nanocomposite. They used this electrode for the analysis

PNCs are widely used these days in DNA biosensors. The medico biological field is growing leaping and bounds. In this era of 23 and me everything possible with DNA is bouncing through the boundaries of technology like DNA CRISPR editing, gene mapping. Biological agents for nefarious purposes and forensics. A basic DNA sensor work on a simple principle. You plant a DNA probe on a surface and this planted DNA chain hybridizes with its complementary pair. This hybridization technically called transduction can be detected optically and electrochemically. The electrochemical detection of transducers through electrochemical sensors leads us to DNA biosensors and are now extremely popular. The recent progress in the stud-

*DOI: http://dx.doi.org/10.5772/intechopen.86826*

of hydroquinone, DA, and nitrobenzene [20].

**3. DNA biosensors**

to the release of Ag<sup>+</sup>

from 150 × 10<sup>−</sup>12 to 1 × 10−<sup>6</sup>

*Polymer nanocomposite-based DNA sensors [1].*

pemetrexed (PMX). The results showed that overoxidation of the PPy film conferred a negative charge density on the porous layer, which in turn enhances the adsorption of PMX [19]. Xu et al. fabricated a carbon paste electrode (CPE) modified with a PEDOT-CNT nanocomposite. They used this electrode for the analysis of hydroquinone, DA, and nitrobenzene [20].
