Graphene and tricobalt tetraoxide nanoparticles based biosensor for electrochemical glutamate sensing

Figures & data

Scheme 1. The fabrication steps of the biosensor.

Figure 1. SEM images of (a) Co₃O₄/CS/GR/GCE and (b) GLOx/Co₃O₄/CS/GR/GCE surfaces.

Figure 2. (A) Cyclic voltammograms of (a) GCE and (b) Co₃O₄/CS/GR/GCE at 50 mV s⁻¹ (B) The Nyquist curves of (a) GCE and (b) Co₃O₄/CS/GR/GCE in 0.1 M KCl solution containing 5.0 mM Fe(CN)₆^3−/4− (C) Peak currents of Co₃O₄/CS/GR/GCE as a function of scan rate for the determination of the effective working surface area. Inset: Cyclic voltammograms of the Co₃O₄/CS/GR/GCE at scan rates of 10, 20, 50, 75, 100, 200, and 300 mV s⁻¹ in a 0.1 M KCl solution containing 5.0 mM Fe(CN)₆^3−/4−.

Figure 3. The effects of (a) enzyme amount (+0.70 V; pH 7.5), (b) buffer pH (+0.70 V), (c) applied potential (pH 7.5), and (d) temperature (+0.70 V; pH 7.5) on the response of GLOx/Co₃O₄/CS/GR/GCE (0.05 M PBS containing 0.2 mM glutamate).

Figure 4. (a) Calibration curve of the GLOx/Co₃O₄/CS/GR/GCE, (b) Typical current–time response of the on successive injection of glutamate into a stirred solution of 0.05 M PBS (pH 7.5) at applied potential +0.70 V, and (c) The effect of glutamate concentration upon the amperometric response of the biosensor (0.05 M pH 7.5 PBS, 37 °C).

Figure 5. The repeatability of the GLOx/Co₃O₄/CS/GR/GCE (0.05 M pH 7.5 PBS, 37 °C).

Table 1. The performance parameters and the optimum working conditions of the biosensor.

Optimum working conditions
Enzyme amount (U)	0.24
Temperature (°C)	37
pH	7.5
Working potential (V)	+0.70 versus Ag/AgCl
Performance factors
Linear range	4.0 × 10^−6 M − 6.0 × 10^−4 M
Limit of detection (LOD)	2.0 × 10^−6 M
Sensitivity (μA/mM and μA/mM cm^2)	0.73; 7.37
Km (mM)	1.09
Response time (s)	25
Repeatability (RSD%)	1.0

Table 2. Characteristics of various amperometric glutamate biosensors.

Electrode	Working potential V	Detection limit	Linear range	Sensitivity	Response time	Km	pH	References
c-MWNCT/AuNPs/CS modified Au electrode	+0.135 versus Ag/AgCl	1.6 μM	5−500 μM	155nA/μM/cm^2	2 s	−	7.5	Batra and Pundir (2013)
Pt nanoparticle modified Au nanowire array electrode	+0.65 versus Ag/AgCl	14 μM	Up to 0.8 μM	10.76 μA/mM cm^2	<5 s	−	7.4	Jamal et al. (2010)
Chip-based amperometric enzyme sensor	+0.6 versus Ag/AgCl	0.05 mM	Up to 10 mM	3.68 μAs/mM	–	−	8.0	Backer et al. (2013)
p-hydroxybenzoate hydroxylase on a Clark-type electrode	−0.6 versus Ag/AgCl	5 μM	10 μM−1.5 mM	–	2 s	−	8.0	Cui et al. (2007)
A photo-crosslinkable polymer membrane modified biosensor	+0.4 versus Ag/AgCl	0.05 μM	0.05−100 μM	12.18 nA/μM	−	−	7.0	Chang and Chen (2007)
A l-GLOx–l-GLDH coupled enzymatic sensor based on oxygen electrode	−	−	0.02−1.2 mg/L	−	2 min	1.92 mM	7.0 ± 2.0	Basu et al. (2006)
Nafion/methyl viologen modified glassy carbon electrode	−0.65 versus Ag/AgCl	20 μM	Up to 75 mM	−	−	2.84 mM	7.4	Maalouf et al. (2007)
Glutamate dehydrogenase/vertically aligned CNTs electrode	−	57 nM	0.1−20 μM 20−300 μM	0.976 mA/mM cm^2 0.182 mA/mM cm^2	−	−	7.0	Gholizadeh et al. (2012)
A tetrafulvalene-tetracyanoquinodimethane carbon paste electrode	−	0.15 mmol L^−1	−	−	20−50 s	−	7.0	Pauliukaite et al. (2006)
GLDH and poly(amidoamine) dendrimer-encapsulated platinum nanoparticle onto CNTs	+0.2 versus Ag/AgCl	10 nM	0.2−250 μM	433 μA/mM cm^2	3 s	−	7.4	Tang et al. (2007)
Microbiosensor based on our sol–gel electrodeposition technique	+0.6 versus Ag/AgCl	5 nM	0.5−100 μmol/L	279.4 ± 2.0 A (mmol L^−1)^−1 cm^−2	10 s	0.776 mM	7.4	Tian et al. (2009)
CS enzyme film modified Pt electrode	+0.4 versus Ag/AgCl	1 × 10^−7 M	5 × 10^−7−2 × 10^−4 M	85 mA/M cm^2	2 s	−	7.4	Zhang et al. (2006)
GLOx/nano conducting polymer/Pt microbiosensor	+0.45 versus Ag/AgCl	0.1 ± 0.03 μM	0.2−100 μM	−	10 s	−	7.4	Rahman et al. (2005)
Co3O4 nanoparticles and GR modified GCE	+0.7 versus Ag/AgCl	2 × 10^−6 M	4 × 10^−6−6 × 10^−4 M	0.73 μA/mM 7.37 μA/mM cm^2	25 s	1.09 mM	7.5	This work

c-MWCNTs: Carboxylated carbon nanotubes; GR: Graphene; CNTs: Multiwall carbon nanotubes; AuNPs: Gold nanoparticles; CS: Chitosan; Au: gold electrode; l-GLDH: l-glutamate dehydrogenase.

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