3D graphene oxide-cobalt oxide polyhedrons for ...

Sensors and Actuators B 253 (2017) 773–783

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3D graphene oxide-cobalt oxide polyhedrons for highly sensitive non-enzymatic electrochemical determination of hydrogen peroxide Sakthivel Kogularasu a , Mani Govindasamy a , Shen-Ming Chen a,∗ , Muthumariappan Akilarasan a , Veerappan Mani a,b,∗ a b

Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, Taipei, 106, Taiwan, ROC Graduate Institute of Biomedical and Biochemical Engineering, National Taipei University of Technology, Taipei, Taiwan, ROC

a r t i c l e

i n f o

Article history: Received 2 April 2017 Received in revised form 25 May 2017 Accepted 26 June 2017 Available online 28 June 2017 Keywords: Graphene/metal oxide Non-enzymatic sensing Hydrogen peroxide Cell signaling molecule Chemical sensor Analytical chemistry

a b s t r a c t Polyhedrons structured cobalt oxide (Co3 O4 PHs) and three-dimensional graphene oxide encapsulated cobalt oxide polyhedrons (3D GO-Co3 O4 PHs) were synthesized via facile hydrothermal synthetical route for the highly sensitive determination of hydrogen peroxide (H2 O2 ). The morphological study clearly revealed the polyhedron shaped Co3 O4 and additionally elemental, diffraction, and electrochemical studies were performed to verify the structure and shape. Owing to excellent synergy between Co3 O4 PHs and GO, the composite possesses good porosity, large electrochemical area, roughened surface, and excellent electrocatalytic ability. The development of highly sensitive sensor is essential for H2 O2 due to its great significance in physiological, biochemical, pharmaceutical and medicinal applications. A rapid, sensitive, selective, reproducible, and durable non-enzymatic H2 O2 assay, by employing 3D GO-Co3 O4 PHs modified electrode was described. The sensor offered excellent sensitivity with detection limit of 15 nM, which is superior to those of previously reported sensors. A real-time analysis was demonstrated in commercially acquired contact lens and disinfectant cleaning solutions without pre-treatment. © 2017 Elsevier B.V. All rights reserved.

1. Introduction Hydrogen peroxide (H2 O2 ) plays vital functions in biological systems, industrial, pharmaceutical, and etc., [1]. it is widely used in many healthcare products ascribed to its antiseptic and antibacterial properties [2]. In biochemistry, it belongs to reactive oxygen species (ROS) released as byproducts during metabolism. H2 O2 is an important cell signaling molecule and playing vital roles in the regulation of cell-signaling processes. However, its overproduction and accumulation in body causes severe damages to the cells that causes several dangerous diseases such as, Alzheimer’s disease, Parkinson’s disease, cancer, cardiovascular disease, and etc., [3] and it is a biomarker of oxidative stress [4]. Besides, H2 O2 is an oxidizing agent for horseradish peroxidase (HRP), which is a popular tag enzyme in molecular biology. Certainty, sensitive determination of H2 O2 is highly important. Several analytical methods have been developed for H2 O2 determination, such as spectrophotometry, chemiluminescence, fluorescence, electrochemical, etc. Electrochemical methods are low-cost, portable,

∗ Corresponding authors at: Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, Taipei, 106, Taiwan, ROC E-mail addresses: [email protected] (S.-M. Chen), [email protected] (V. Mani). http://dx.doi.org/10.1016/j.snb.2017.06.172 0925-4005/© 2017 Elsevier B.V. All rights reserved.

easy-to-use, fast, direct digital signal, miniaturizable and less power consumption. Enzymatic biosensors encounter issues such as, enzyme instability on solid electrodes, tedious immobilization procedures, denaturation, lack of durability, storage stability, cost, and poor tolerance to non-physiological chemical environments i.e, temperature, pH, humidity, etc. [5]. Recently increasing interest has been focused on the development of non-enzymatic H2 O2 sensors based on metal oxide based electrodes [6]. Several studied proved that Co3 O4 catalyzes the enzymeless H2 O2 reduction and they able to minimize overpotential and surface fouling, improve selectivity, and amplify signal sensitivity. Co3 O4 based electrodes for H2 O2 sensing are, Urchin-like Co3 O4 nanostructures [7], nafion/GO/Co3 O4 [8], Co3 O4 /MWCNTs [9], 3D hierarchical porous Co3 O4 nanostructure [10], Co3 O4 sphere and cube [11], microporous Co3 O4 @Pd nanoparticles [12], 1D Co3 O4 nanowires/RGO [13] and Co3 O4 porous nanoribbons/reduced graphene oxide [14]. Regardless of the reported sensors, the robust and real-time applicable non-enzymatic H2 O2 sensor is yet to be developed. The controlled syntheses of nanomaterials to implement desired structure, shape, and size is an important topic in material science research, as the morphology has profound impact on the performance of that material in any desired applications [15–17]. Over the past years, different shapes of cobalt oxide (Co3 O4 ) such as, nanoparticles [18], flowers [19], nanosheets [20,21],

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nanoflakes [22], nanofibers [23], microspheres [24], nanocubes [25,26], nanowall arrays [17], mesoporous hollow spheres [27], nanorings [28], nanograin [15], nanorods [29] and microrods [30] have been prepared on graphene or graphene oxide (GO) sheets by either altering preparation strategies or tuning experimental conditions and precursors. For instance, Co3 O4 nanowires were synthesized by hydrothermal procedure on 3D graphene foam grown by chemical vapor deposition (CVD) [5]. A mesoporous hollow Co3 O4 spheres were synthesized by a surfactant-assisted solvothermal method [27]. A 3D porous Co3 O4 architecture was prepared through leaf-templated strategy [10], while 1D Co3 O4 nanowires on reduced graphene oxide (RGO) was prepared via hydrothermal method. Recently, the green synthesis of Co3 O4 nano hexagons was reported by our research group [31]. However, polyhedrons structured Co3 O4 has never been reported in literature. Graphene is likely to remain one of the leading subjects in materials science for many years [32–35]. The electrochemical properties of graphene or GO can be further upgraded by tailoring them with metal oxides such as, Co3 O4 [36,37]. Specially, graphene supported Co3 O4 attracted considerable attention in many fields because Co3 O4 materials are low-cost, earth abundant, highly stable, and holding excellent electrocatalytic property for several important reactions [5,14,15,26,38]. For the first time, we are reporting the synthesis of polyhedrons shaped Co3 O4 via hydrothermal route and the synthesis is simple, fast, mass producible, green and straightforward. Moreover, 3D porous network of GO encapsulated Co3 O4 polyhedrons (PHs) was configured which was exploited to setup a highly sensitive and cost-effective enzymeless H2 O2 amperometric sensing platform for the determination of hydrogen peroxide (H2 O2 ) (Scheme 1). The composite possess high porosity, roughed structure, interconnected network, large electrochemical active area, high defect density and superior electrocatalytic ability. Intrinsic peroxidase catalytic activity of GO was uncovered [39] and hence GO was selected over graphene, additionally GO offers several advantages such as, aqueous solution processability, low-cost synthesis from graphite, abundant oxygen functionalities, high edge defects and sites for functionalization. 2. Experimental 2.1. Chemicals and instrumentation (powder, 3D GO-Co3 O4 PHs/SPCE (308.8 ) > Co3 O4 PHs/SPCE (144.1 ). The Rct value of 3D GO-Co3 O4 PHs/SPCE was much smaller than those of GO which indicating a lower diffusion resistance and charge-transfer resistance.

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illustrated in Fig. 6B. The CV of GO showed poor current background due to its insulating nature. The CV of 3D GO-Co3 O4 PHs exhibited significantly enhanced background current. Moreover, two redox couples, I/II and II/IV were observed which were manifested to the reversible reactions of Co3 O4 /CoOOH and CoOOH/CoO2 , respectively that are characteristic voltammetric behaviour of electrochemically active Co3 O4 . The corresponding equations can be given as, Co3 O4 + OH− + H2 O3CoOOH + e− and CoOOH + OH− CoO2 + H2 O + e− [5]. As the scan rate increased, the redox peak currents increased indicating surface-confined electrochemical process (Fig. 6C). The electrochemically effective surface areas of Co3 O4 PHs/SPCE, GO/SPCE and 3D GO-Co3 O4 PHs/SPCE were assessed using K3 [Fe(CN)6 ] as a model redox mediator and they were calculated to be 0.095, 0.106 and, 0.146 cm2 , respectively. Indeed, the electrochemically active area of 3D GO-Co3 O4 PHs/SPCE is significantly improvement as compared with the individual constituents and this result implied that the modified electrode is suitable for electrochemical applications. 3.8. Electrocatalysis of H2 O2 reduction Fig. 6D displayed the CVs recorded for unmodified SPCE (a), GO/SPCE (b), Co3 O4 PHs/SPEC (c), and 3D GO Co3 O4 PHs/SPCE (d) measured at a scan rate of 50 mV s−1 in the potential range of 0 to −0.9 V. The supporting electrolyte comprised 50 ␮M H2 O2 . The trend of electrocatalytic ability: 3D GO-Co3 O4 PHs/SPCE> Co3 O4 PHs> GO/Co3 O4 PHs> unmodified SPCE. The 3D GO-Co3 O4 PHs/SPCE offered great advantageous to H2 O2 reduction as it exhibited highly enhanced electrocatalytic ability and fast electron transfer. In fact, the reduction current obtained at 3D GO Co3 O4 PHs/SPCE was 24, 3.4, and 3 folds higher than those obtained at unmodified, GO and Co3 O4 PHs films modified SPCEs, respectively. Moreover, the overpotential observed at 3D GO-Co3 O4 PHs/SPCE was 240, 130, and 50 mV lower than those obtained at unmodified, GO and Co3 O4 PHs modified SPCEs, respectively. The improved electrocatalytic ability of the composite can be manifested to the great synergetic effect and proper tailoring of GO with Co3 O4 PHs. Thus, the GO sheets are highly suitable support for loading Co3 O4 PHs. Fig. 6E presented the CVs obtained at 3D GO-Co3 O4 PHs/SPCE in 0.1 M PB (pH 7.0) containing various concentrations of H2 O2 . The cathodic peak current was linearly increased as the concentration of H2 O2 increased. The effect of scan rate towards the H2 O2 reduction was studied by applying different scan rates from 20 to 200 mV s−1 (Fig. 6F). The plot between cathodic peak current and square root of scan rate exhibited good linearity indicating diffusion controlled reduction process (inset to Fig. 6F). 3.9. Amperometric determination of H2 O2

Fig. 4. XRD (A), Raman (B) and FT-IR spectra (C) of GO, Co3 O4 PHs and 3D GO-Co3 O4 PHs.

3.7. Electrochemical activity of 3D GO-Co3 O4 PHs The cyclic voltammograms (CVs) of GO/SPCE (a), Co3 O4 PHs (b), and 3D GO-Co3 O4 PHs (c) films modified electrodes over a potential range of 0–0.6 V at a scan rate of 50 mV s−1 were

Fig. 7A presented amperometric response of the 3D GO-CO3 O4 PHs modified electrode (rotation speed = 1200 RPM) upon successive injections of H2 O2 into PB (pH 7) at a regular intervals of 50 s (Eapp = −0.52 V). Well-defined and quick responses were obtained and steady-state current was reached in less than 5 s. Two linear ranges were obtained. The first linear range at low concentration region was 0.05–400 ␮M with sensitivity of 3.45 ␮A␮M−1 cm−2 (inset to Fig. 7A). The second linear range at higher concentration region was 450–1250 ␮M with sensitivity of 2.12 ␮A ␮M−1 cm−2 (Fig. 7B). The limit of detection (LOD) was calculated to be 15 nM. Such a low detection limit at nanomolar level illustrated the outstanding sensing performance of the electrode. The sensor parameters were superior over previously reported H2 O2 sensors including other metal oxide based modified electrodes. The superior sensing property of this electrode can be ascribed to the three dimensional hierarchical network of composite, good porosity, excellent synergistic effect between GO and CO3 O4 PHs, improved


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Fig. 5. (A) XPS survey spectrum of 3D GO-Co3 O4 PHs, (B) C 1s, (C) O 1s and (D) Co 2p.

surface area and good electrocatalytic properties. Additionally, the oxygen functionalities located on basal and edges planes of GO able to supply additional sites for electrocatalysis by several possible interactions. The selectivity of the sensor was evaluated by performing the interference experiments in presence of likely interfering agents. Fig. 7C showed the amperometric response of the electrode towards 5 ␮M of H2 O2 (a), and 500 ␮M of dopamine (b), uric acid (c), ascorbic acid (d), NADH (e), folic acid (f), cysteine (g), epinephrine (h), guanine (i), pyridoxine (j), cholesterol (k), norepinephrine (l), and nitrite (m). The electrode quickly responded to H2 O2 ; however, it was insensitive the other species, thus, the electrode specifically recognizes and sensed H2 O2 in the pool of other biological analytes (Table 1). 3.10. Durability, reproducibility and repeatability In order to evaluate durability of the sensor, to find out the storage stability of the electrode The sensor performance of the 3D GO-CO3 O4 PHs modified electrode was monitored every week, while the electrode was stored at 4 ◦ C when not in use. The electrode retained 94.5% of its initial current even after 9 weeks of its continuous use, which endorsed excellent durability (inset to Fig. 7C). For the reproducibility studies, measurements at five individual electrodes were recorded in PB (pH 7.0) towards 10 ␮M H2 O2 ; the R.S.D was 3.4%. In order to calculate repeatability, five

repeated measurements were performed at one modified electrode; the R.S.D was 3.5%. Accordingly, the sensor has acceptable range of repeatability and reproducibility. 3.11. Real-time applicability The practical feasibility of the fabricated sensor was demonstrated in contact lens (Fig. 8A) and disinfectant solutions (Fig. 8D). These solutions already contained inherent H2 O2 and hence directly spiked into the supporting electrode and amperometry experiments were performed by following the optimized experimental conditions of lab samples. Similar to lab samples, both the real samples showed quick and sensitive signals within 5s. Notably, the real samples have not undergone any pre-sampling procedures. Regardless, the sensor results were consistent with those of lab samples indicating sensitive and selective detection of H2 O2 in contact lens and disinfectant cleaning solutions. For contact lens cleaning solution, the linear ranges were 0.15–210 ␮M and 230–725 ␮M with sensitivities of 2.31 and 1.44 ␮A␮M−1 cm−2 (Fig. 8B,C), while the LOD was calculated to be 40 nM. For disinfectant solution, the linear ranges were 0.12–200 ␮M and 250–810 ␮M with sensitivities of 2.68 and 1.14 ␮A␮M−1 cm−2 (Fig. 8E,F), while the LOD was calculated to be 33 nM. Next, the real sample analysis results obtained using our method was compared with standard method. Standard titration method in acidic media was adopted (2MnO4 − + 5H2 O2 + 6H+ → 2Mn2+ + 5O2 + 8H2 O) [48,51]. As shown

Table 1 Comparison of analytical parameters at 3D GO-Co3 O4 PHs modified electrode with previously reported H2 O2 sensors. Electrode

Detection limit/␮M

Linear range/␮M

Ref

Co3 O4 spheres CoFe2 O4 /Exfoliated graphene oxide MnO2 nanowires/graphene paper ZnO nanosheets 3D graphene/Fe3 O4 quantum dots Porous silicon/Ag nanocomposite Cu nanoparticle decorated anchored type ligands copper/porous silicon Pt-Cu@silicon nanostructure Nf/Porous Co3 O4 nanoparticles CuS/reduced graphene oxide Co3 O4 cube/Nf Pd@ Co3 O4 hollow spheres Co3 O4 nanowires/reduced graphene oxide CoOOH nanosheets 3D GO-Co3 O4 PHs

0.145 0.54 10 0.8 0.078 0.45 0.85; 0.27 0.27 0.1 0.24 0.1 1.208 1 2.4 40 0.015

0.1–50 0.9–900.0 100–45400 1–1000 0.8–334.4 1.65–500 5.14–1250; 1.14–1120 0.50–3780 0.5–1280 1–300 1–1000 4–288 1–330 15–675 4–16 0.05–400; 450–1250

[7] [42] [43] [44] [45] [46] [47] [48] [6] [10] [49] [11] [12] [13] [50] This work

Table 2 Determination of H2 O2 in contact lens (Fig. 8A) and disinfectant solutions. Real sample

Titration method (␮M)

Proposed method (␮M)

Recovery (%)

R.S.D. (%a )

contact lens cleaning solution disinfectant solutions

12.4 22.5

11.8 21.4

95.7 95.11

4.8 4.7

a

R.S.D. = Relative standard deviations of three individual measurements.

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Fig. 6. (A) EIS spectra of GO (a), Co3 O4 PHs (b), and 3D GO-Co3 O4 PHs (c), Inset: Randles equivalent circuit model, Rs , Rct Cdl and Zw were electrolyte resistance, charge transfer resistance, double layer capacitance and Warburg impedance, respectively. (B) CVs obtained at GO/SPCE (a), Co3 O4 PHs/SPCE (b), and 3D GO-Co3 O4 PHs/SPCE (c) in 0.1 M KOH at a scan rate of 50 mV s−1 , (C) Effect of the scan rate: CVs of 3D GO-Co3 O4 PHs/SPCE in 0.1 M KOH at different scan rates (a–j; 10–100 mV s−1 ). (D) CVs obtained at unmodified SPCE (a), GO/SPCE (b), Co3 O4 PHs/SPCE (c) and 3D GO-Co3 O4 PHs/SPCE (d) in 0.1 M PB (pH 7.0) containing 50 ␮M H2 O2 . (E) CVs of 3D GO-Co3 O4 PHs/SPCE in 0.1 M PB (pH 7.0) containing different concentrations of H2 O2 (a = 50, b = 100, c = 150, d = 200 and e = 250 ␮M). Inset = current vs. [H2 O2 ] (F) CVs of 3D GO-Co3 O4 PHs/SPCE in 0.1 M PB (pH 7.0) containing 50 ␮M H2 O2 at different scan rates (a to j; 50–500 mV s−1 ), Inset = (scan rate)1/2 /(V s−1 )1/2 vs. peak currents/␮A.

in Table 2, the acceptable range of recoveries was obtained comparable to standard method, which validated the accuracy of the described method. Meeting the demand for cost-effective, robust and portable analytical devices, our enzymeless electrochemical sensor developed herein based on 3D GO Co3 O4 PHs/SPCE has enormous potential as useful sensing tool for real time on-line monitoring of H2 O2 .

4. Conclusions A facile hydrothermal synthetical route was described to prepare polyhedrons shaped Co3 O4 Phs and 3D GO-Co3 O4 Phs composite and its successful formation was confirmed by morphological, elemental, spectral and electrochemical methods. The 3D GO-Co3 O4 Phs film modified electrode shown good electrochemical


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Fig. 7. (A) Amperometric response of 3D GO-CO3 O4 PHs film modified electrode for each sequential additions of H2 O2 into 0.1 M PB (pH 7.0). Electrode rotation speed = 1200 RPM and applied potential = −0.52 V, Inset: [H2 O2 ] (␮M) vs. current (␮A). (B) Calibration plot at high concentration region. (C) Amperometric response of 3D GO-CO3 O4 PHs towards 5 ␮M of H2 O2 (a), and 500 ␮M of dopamine (b), uric acid (c), ascorbic acid (d), NADH (e), folic acid (f), cysteine (g), epinephrine (h), guanine (i), pyridoxine (j), cholesterol (k), norepinephrine (l), and nitrite (m), Inset: Storage stability.

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Fig. 8. Real sample analysis: Contact lens cleaning solution (C) and disinfectant cleaning solution (D), amperometric response of 3D GO-Co3 O4 PHs/SPCE for each sequential addition of real samples into PB (pH 7.0). Calibration plots: Contact lens cleaning solution (E) and disinfectant cleaning solution (F).

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Biographies

Mr. Kogularasu Sakthivel is currently a Ph.D student in the Department of Chemical Engineering, National Taipei University of Technology, Taiwan. He received his B.Sc degree (chemistry) in 2014 and M.Sc degree (chemistry) in 2016 from Bishop Heber College, India. His research interests include nanomaterials synthesis, electrochemical sensors and biosensors and energy storage devices.

Mr. Mani Govindasamy received his B.S. Degree in Chemistry from St. Joseph’s College, (Bharathidasan University) Tamil Nadu, India, in 2013 and M.S. Degree in Bishop Heber College, (Bharathidasan University) Tamil Nadu, India in 2015. Currently he is a Ph.D. student in the Department of Chemical Engineering and Biotechnology National Taipei University of Technology, Taiwan. His research interest mainly focusing on the green synthesis nanoparticles, graphene and molybdenum sheets based composite materials for electrochemical sensor, biosensor and energy applications.

Dr. Shen-Ming Chen received his B.S. Degree in Chemistry in 1980 from National Kaohsiung Normal University, Taiwan. He received his M.S. Degree (1983) and Ph.D. degree (1991) in Chemistry from National Taiwan University, Taiwan. He is currently a professor atthe Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, Taiwan. His current research interests include electroanalytical chemistry, bioelectrochemistry, fabrication of energy conservation and storage devices and nanomaterial synthesis for electrochemical applications. He has published more than 500 research articles in SCI journals. Mr. Akilarasan Muthumariappan received his B.Sc degree in chemistry in 2014 from Bishop heber College, India. He received his M.Sc degree in chemistry in 2016 from Bishop heber college, India. He is currently a Ph.D student in the Department of Chemical Engineering, National Taipei University of Technology, Taiwan. His current research interests includes electroanalytical chemistry, bioelectrochemistry and biosensors

Veerappan Mani received his B.S Degree from Periyar University (2007), and M.S Degree Chemistry from Bharathidasan University (2009), Tamil Nadu, India in Chemistry. Dr. Mani received PhD from Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, Taipei, Taiwan in 2014 and currently he is a research assistant professor. His research interest is mainly focusing on the synthesis of twodimensional layered nanomaterials, nanocomposites and nanohybrids for sensors, biosensors, and energy applications. Dr. Mani has published over 60 peer-reviewed scientific publications in well-reputed SCI journals and presented numerous papers in national and international level conferences. He is serving as editorial board member in several journals.