**2.2 Nanocomposite-based graphene oxide as electrochemical sensors**

## *2.2.1 Detection of proteins*

Gevaerd et al. designed and synthesized imidazole-functionalized graphene oxide (GO-IMZ) as non-enzymatic electrochemical sensor for the detection of progesterone [14]. Progesterone (P4) plays an important role in the stabilization and maintenance of gestation as most important progestogen of mammals. The GO-IMZ complex as an artificial enzymatic active site was reported using voltammetric determination of progesterone. The as-synthesized sensor displayed a synergistic effect of GO nanosheets and imidazole showing the obvious enhancement on the electrochemical response of P4. The electrochemical response signal showed a linear relationship with concentrations of P4 between 0.22 and 14.0 μmol/L. The detection limit was 68 nmol/L. The limit of quantification was 210 nmol/L. The higher sensitivity was presented compared to the unmodified electrode.

Tomita and co-workers designed and reported the construction of high accessible and high tunable multi-fluorescent sensing system, and this sensing system presented protein fluorescent signals from a single microplate well [15]. The principal mechanism of approach was based on three single-stranded DNAs (ssDNAs) functionalized-nano-graphene oxide (nGO). The single-stranded DNAs showed different sequences and functions, and fluorophores exhibited different optical

properties. The fluorescence of three fluorophore-modified ssDNAs was quenched upon conjugation with nGO. The partial recovery of fluorescence intensity of individual ssDNAs was observed upon addition of analyte proteins.

#### *2.2.2 Detection of drug molecules*

Abdallah and Ibrahim designed and developed an imprinted potentiometric sensor for the detection of gabapentin that is an anticonvulsant agent [16]. The sensor was constructed using carbon paste electrode following three steps: (i) the GO was decorated by silver nanoparticles; (ii) silver nanoparticles modified with GO mixed physically with molecularly imprinted polymers nanoparticles with gabapentin as a template molecule and then leached the template molecule; and (iii) the abovementioned mixture deposited on carbon paste electrode. The sensor showed good selectivity and high sensitivity, and the detection limit is 4.8 × 10<sup>−</sup>11 mol/L. Yang and co-workers designed and prepared CdTe quantum dot (QD)-decorated poly(diallyldimethylammonium chloride) (PDDA)-functionalized graphene (CdTe-PDDA-Gr) nanocomposite based on the presence of PDDA and CdTe QDs using chemical reduction of exfoliated graphite oxides [17]. The CdTe-PDDA-Gr nanocomposite showed very fast electron transfer behavior and obvious absorption effect for puerarin due to high surface area and good conductivity. They exhibited very good electrocatalytic behavior toward the oxidation of puerarin. The oxidation peak current showed a good linear relationship with the concentrations of puerarin within 0.001–1.0 μM by differential pulse voltammetry (DPV). The limitation of detection was 0.6 nM (SNR of 3).

The nickel tetra-amined phthalocyanine-graphene oxide covalent compound was developed as a photoelectrochemical sensor for the detection of erythromycin with high sensitivity [18]. The graphene oxide was modified by tetra-amined phthalocyanine (NiTAPc) by covalent bonding getting the final product NiTAPc-Gr. The as-synthesized sensor exhibited a higher photoelectrochemical efficiency and showed a peak wavelength of 456 nm by irritation of visible light. Compared to that of GO/ITO, the photocurrent of NiTAPc-Gr/ITO was 50-fold at the same conditions. The photocurrent showed a good linear relationship with the concentrations of erythromycin between 0.40 and 120.00 μmol/L. The detection limit was 0.08 μmol/L. The constructed photoelectrochemical sensors have been successfully applied to detect erythromycin in human blood plasma.

#### *2.2.3 Detection of the other small molecules*

A bimetallic electrochemical sensor was designed and constructed for the sensitive detection of uric acid (UA) with high selectivity [19] as shown in **Figure 5**. The bimetallic nanoparticles (NPs) were synthesized by electrodeposition on the glassy carbon electrode (GCE) using the HAuCl4 and AgNO3 as precursors by co-reduction through cyclic voltammetry scanning. Firstly, the GO-TH complex was formed by electrostatic interactions between GO and thionine (TH); then, the GO-TH complex was drop-coated on Au-Ag NPs to construct Au-Ag NPs/GO/TH@GCE. The redox current peak intensity showed regular increase with the increase of concentration of UA. The good linear relationship was exhibited between *IUA*/*ITH* and [UA] within 1–100 μM with linearly plotted (R2 = 0.9929). The detection limit was 0 .3 μM.

A non-enzymatic sialic acid (SA) electrochemical sensor was designed and constructed based on indicator displacement assay (IDA) of dopamine with high sensitivity and high selectivity [20]. The mechanism of SA detection was based on reversible covalence with boronic acid-diol complex. In other words, the SA and DA all can covalently interact with 2-fluorophenylboronic acid (FPBA) by replacing of 1,2-diols. The electrode was constructed and synthesized based on

**179**

**Figure 5.**

Au/CS-GO sensor was 7 × 105

even on the presence of other species.

*Nanocomposite-Based Graphene for Nanosensor Applications*

tetra(4-carboxyphenyl) porphine-graphene oxide (TCPP-GO), DA, and FPBA on the surface of glassy carbon electrode (GCE), respectively. The TCPP-GO complex obviously enhanced the sensitivity of the electrochemical sensor. The recovered anodic current intensity of DA showed a good linear relationship with the concentration of SA within 0.1–7.5 mM. The detection limit was 28.5 μM. The sensor has

*Illustration of the preparation and applications of the Au-Ag NPs/GO/TH@GCE sensing platform.*

The gold/silver/gold/chitosan-graphene oxide (Au/Ag/Au/CS-GO) sensor was designed and constructed for the detection of Pb2+ and Hg2+ ions with high sensitivity [21]. The higher affinity constant of Pb2+ binding with the CS-GO showed higher affinity than that of Hg2+ binding with the CS-GO. The maximum S/N was 1.53. The Au/Ag/Au/CS-GO surface plasmon resonance (SPR) sensor displayed good repeatability toward Pb2+ ions due to the coordination interaction. The adsorption behaviors of Pb2+ and Hg2+ ions onto the surface of CS-GO sensor fit to the Langmuir isotherm model. The affinity constant of Pb2+and Hg2+ to bind Au/Ag/

and 4 × 105

and prepared a voltammetric sensor based on graphene oxide/κ-carrageenan/lcysteine nanocomposite (GO/κ-Car/l-Cys) for the detection of Cd2+ and Pb2+ ions [22]. The GO/κ-Car/l-Cys composite modified with glassy carbon electrode (GCE) was successfully synthesized. The electrochemical response of GO/κ-Car/l-Cys composite showed a good linear relationship with the concentrations of Cd2+ and Pb2+ ions within 5–50 nM, and the detection limit was 0.58 and 1.08 nM for Cd2+ and Pb2+ ions, respectively. The sensitivity for Cd2+ and Pb2+ ions was 1.39 μA/nM and 1.32 μA/nM, respectively. The interference experiment results showed no affect

M<sup>−</sup><sup>1</sup>

, respectively. Priya et al. resigned

been successfully applied to detect SA in human blood and urine samples.

M<sup>−</sup><sup>1</sup>

*DOI: http://dx.doi.org/10.5772/intechopen.85136*

*Nanocomposite-Based Graphene for Nanosensor Applications DOI: http://dx.doi.org/10.5772/intechopen.85136*

*Nanorods and Nanocomposites*

*2.2.2 Detection of drug molecules*

properties. The fluorescence of three fluorophore-modified ssDNAs was quenched upon conjugation with nGO. The partial recovery of fluorescence intensity of

Abdallah and Ibrahim designed and developed an imprinted potentiometric sensor for the detection of gabapentin that is an anticonvulsant agent [16]. The sensor was constructed using carbon paste electrode following three steps: (i) the GO was decorated by silver nanoparticles; (ii) silver nanoparticles modified with GO mixed physically with molecularly imprinted polymers nanoparticles with gabapentin as a template molecule and then leached the template molecule; and (iii) the abovementioned mixture deposited on carbon paste electrode. The sensor showed good selectivity and high sensitivity, and the detection limit is 4.8 × 10<sup>−</sup>11 mol/L. Yang and co-workers designed and prepared CdTe quantum dot (QD)-decorated poly(diallyldimethylammonium chloride) (PDDA)-functionalized graphene (CdTe-PDDA-Gr) nanocomposite based on the presence of PDDA and CdTe QDs using chemical reduction of exfoliated graphite oxides [17]. The CdTe-PDDA-Gr nanocomposite showed very fast electron transfer behavior and obvious absorption effect for puerarin due to high surface area and good conductivity. They exhibited very good electrocatalytic behavior toward the oxidation of puerarin. The oxidation peak current showed a good linear relationship with the concentrations of puerarin within 0.001–1.0 μM by differential pulse voltammetry

The nickel tetra-amined phthalocyanine-graphene oxide covalent compound was developed as a photoelectrochemical sensor for the detection of erythromycin with high sensitivity [18]. The graphene oxide was modified by tetra-amined phthalocyanine (NiTAPc) by covalent bonding getting the final product NiTAPc-Gr. The as-synthesized sensor exhibited a higher photoelectrochemical efficiency and showed a peak wavelength of 456 nm by irritation of visible light. Compared to that of GO/ITO, the photocurrent of NiTAPc-Gr/ITO was 50-fold at the same conditions. The photocurrent showed a good linear relationship with the concentrations of erythromycin between 0.40 and 120.00 μmol/L. The detection limit was 0.08 μmol/L. The constructed photoelectrochemical sensors have been successfully

A bimetallic electrochemical sensor was designed and constructed for the sensitive detection of uric acid (UA) with high selectivity [19] as shown in **Figure 5**. The bimetallic nanoparticles (NPs) were synthesized by electrodeposition on the glassy carbon electrode (GCE) using the HAuCl4 and AgNO3 as precursors by co-reduction through cyclic voltammetry scanning. Firstly, the GO-TH complex was formed by electrostatic interactions between GO and thionine (TH); then, the GO-TH complex was drop-coated on Au-Ag NPs to construct Au-Ag NPs/GO/TH@GCE. The redox current peak intensity showed regular increase with the increase of concentration of UA. The good linear relationship was exhibited between *IUA*/*ITH* and [UA] within

A non-enzymatic sialic acid (SA) electrochemical sensor was designed and constructed based on indicator displacement assay (IDA) of dopamine with high sensitivity and high selectivity [20]. The mechanism of SA detection was based on reversible covalence with boronic acid-diol complex. In other words, the SA and DA all can covalently interact with 2-fluorophenylboronic acid (FPBA) by replacing of 1,2-diols. The electrode was constructed and synthesized based on

= 0.9929). The detection limit was 0 .3 μM.

individual ssDNAs was observed upon addition of analyte proteins.

(DPV). The limitation of detection was 0.6 nM (SNR of 3).

applied to detect erythromycin in human blood plasma.

*2.2.3 Detection of the other small molecules*

1–100 μM with linearly plotted (R2

**178**

**Figure 5.** *Illustration of the preparation and applications of the Au-Ag NPs/GO/TH@GCE sensing platform.*

tetra(4-carboxyphenyl) porphine-graphene oxide (TCPP-GO), DA, and FPBA on the surface of glassy carbon electrode (GCE), respectively. The TCPP-GO complex obviously enhanced the sensitivity of the electrochemical sensor. The recovered anodic current intensity of DA showed a good linear relationship with the concentration of SA within 0.1–7.5 mM. The detection limit was 28.5 μM. The sensor has been successfully applied to detect SA in human blood and urine samples.

The gold/silver/gold/chitosan-graphene oxide (Au/Ag/Au/CS-GO) sensor was designed and constructed for the detection of Pb2+ and Hg2+ ions with high sensitivity [21]. The higher affinity constant of Pb2+ binding with the CS-GO showed higher affinity than that of Hg2+ binding with the CS-GO. The maximum S/N was 1.53. The Au/Ag/Au/CS-GO surface plasmon resonance (SPR) sensor displayed good repeatability toward Pb2+ ions due to the coordination interaction. The adsorption behaviors of Pb2+ and Hg2+ ions onto the surface of CS-GO sensor fit to the Langmuir isotherm model. The affinity constant of Pb2+and Hg2+ to bind Au/Ag/ Au/CS-GO sensor was 7 × 105 M<sup>−</sup><sup>1</sup> and 4 × 105 M<sup>−</sup><sup>1</sup> , respectively. Priya et al. resigned and prepared a voltammetric sensor based on graphene oxide/κ-carrageenan/lcysteine nanocomposite (GO/κ-Car/l-Cys) for the detection of Cd2+ and Pb2+ ions [22]. The GO/κ-Car/l-Cys composite modified with glassy carbon electrode (GCE) was successfully synthesized. The electrochemical response of GO/κ-Car/l-Cys composite showed a good linear relationship with the concentrations of Cd2+ and Pb2+ ions within 5–50 nM, and the detection limit was 0.58 and 1.08 nM for Cd2+ and Pb2+ ions, respectively. The sensitivity for Cd2+ and Pb2+ ions was 1.39 μA/nM and 1.32 μA/nM, respectively. The interference experiment results showed no affect even on the presence of other species.
