Hierarchical flower-like NiO hollow microspheres for non-enzymatic glucose sensors

    Hierarchical flower-like NiO hollow microspheres for non-enzymatic glucose sensor Zhenzhen Cui, Haoyong Yin, Qiulin Nie, Dongyu Qin, Weiwei Wu, Xiaolong He PII: DOI: Reference:

S1572-6657(15)30107-7 doi: 10.1016/j.jelechem.2015.09.011 JEAC 2274

To appear in:

Journal of Electroanalytical Chemistry

Received date: Revised date: Accepted date:

5 April 2015 5 September 2015 7 September 2015

Please cite this article as: Zhenzhen Cui, Haoyong Yin, Qiulin Nie, Dongyu Qin, Weiwei Wu, Xiaolong He, Hierarchical flower-like NiO hollow microspheres for non-enzymatic glucose sensor, Journal of Electroanalytical Chemistry (2015), doi: 10.1016/j.jelechem.2015.09.011

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ACCEPTED MANUSCRIPT Hierarchical flower-like NiO hollow microspheres for non-enzymatic

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glucose sensor Zhenzhen Cui, Haoyong Yin, Qiulin Nie*，Dongyu Qin，Weiwei Wu，Xiaolong He

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College of Materials & Environmental Engineering, Hangzhou Dianzi University, Hangzhou,

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310018, P. R. China

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Abstract

Hierarchical flower-like NiO hollow microspheres were controllably prepared by a

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facile hydrothermal method using carbon sphere as template. Their structure and

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properties for non-enzymatic glucose sensors were investigated. The results showed

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that the hierarchical flower-like NiO hollow microspheres are composed of the interconnecting porous NiO nanoplates and each nanoplate is assembled by NiO

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nanoparticles with the length of about 12.5nm and the width of about 10nm. Furthermore, the hierarchical flower-like NiO hollow microspheres obtained at different temperature were analyzed with the electro-catalytic activity toward the oxidation of glucose in alkaline solution, and the glucose sensor with hierarchical flower-like NiO hollow microspheres obtained at 550℃ exhibits the best performance with the linear range of 5µM-364µM and sensitivity of 288.87mA mM-1 cm-2. The sensor is also used for detection of glucose with a relatively concentration ranging from 2.96mM to 7.46mM and sensitivity of 37.82mA mM-1 cm-2. More importantly, long-term stability and favorable anti-interference were obtained as a result of the hierarchical hollow structure. Corresponding Author：Qiulin Nie E-mail address: [email protected] Phone numbers: +86-0571-86919125

ACCEPTED MANUSCRIPT Keywords: NiO；Hollow microspheres；Non-enzymatic；Glucose sensor

1. Introduction

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Development of glucose sensors is of great importance in various fields, including

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environmental monitoring, clinical diagnostics and food industry [1-3]. Compared

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with other methods, electrochemical technique is a promising tool for the construction of simple and low-cost sensors due to its high sensitivity, good selectivity and ease of

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operation [4-6]. Generally, electrochemical sensors for glucose determination are

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classified into two major types: enzymatic and non-enzymatic modified sensors. Owing to its high selectivity and fast response to enzyme reaction, glucose oxidase

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(GOD) is always used in enzymatic modified sensor, in which glucose reacts with

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oxygen to produce glucolactone with the catalyzing assistance of GOD [7-9].

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However, the activity of enzymatic glucose sensor is extremely sensitive to environmental conditions and highly dependent on the enzyme immobilization techniques which result in poor stability, high cost and complex fixed technique [10-12].

To solve this problem, considerable interest has been paid on non-enzymatic glucose sensors. Recently, many transition metals and transition metal oxides are used as non-enzymatic sensor materials to determine glucose based on their excellent electrochemical activity [13-15]. Among them Ni-based nanomaterials exhibited remarkably catalytic oxidation activity over glucose as a result of the catalytic effect originating from the formation of the redox couple of Ni(II)/Ni(III) on the electrode surface in alkaline medium[16-17].

ACCEPTED MANUSCRIPT It is well known that the nano/microstructure materials exhibit special properties compared to the relatively bulky materials, which may enhance the electrochemical

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performance. Some non-enzymatic glucose sensors have been successfully developed

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by using NiO-based materials with various structures, such as nanofibers [18-19],

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nanoparticles [4, 20-21], nanoflake arrays [22] and so on. In addition, hollow-sphere structured NiO materials have also been intensively investigated due to their novel

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interior geometry and surface functionality [23-25]. But the organic matters are

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induced as the morphology oriented agent to acquire the hollow structure. This procedure pollutes the final products and imposes restrictions on the sensing property

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to some degree, although they comparatively made progress in their work.

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Inspired by the previous works, hierarchical flower-like NiO hollow microspheres

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were synthesized with carbon sphere as template via a facial hydrothermal method. We further discussed the influence of different temperature in the formation of the special structure and explained the mechanism. The constructed NiO hollow microspheres with the hierarchical flower-like structure have the best electrochemical property in our series glucose sensors, and are especially outstanding on sensitivity compared with the other non-enzymatic glucose sensors [13-14, 16-17] due to the special morphology and structure.

2. Experimental part 2.1. Chemicals and apparatus Nickel chloride hexahydrate (NiCl2•6H2O), sodium hydroxide (NaOH), urea, ascorbic acid, L-leucine, NaCl, L-lysine, L-proline, sucrose and glucose were

ACCEPTED MANUSCRIPT purchased from Aldrich (Milwaukee, WI, USA). All reagents were of analytical grade and used as received without further purification. And all solutions were prepared

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with deionized water.

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The morphology of as-prepared materials was observed by scanning electron

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microscopy (SEM) on S-4700, operated at an accelerating voltage of 15 KV. Transmission electron microscopy (TEM) measurement was carried out with H-008.

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The chemical compositions of the prepared NiO/C microspheres were determined by

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energy dispersive X-ray (EDX). Powder X-ray diffraction (XRD) datum was recorded on DX-2600 with Cu Kα radiation (λ=0.15406nm) to get the crystallographic

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characteristics of the samples. Thermogravimetric analysis (TGA) was carried out on

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a TGA/DSC LF 1600 system at a rate of 10℃min-1 from 50℃ to 700℃ in nitrogen.

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Electrochemical measurements were performed with a CHI630D analyzer (Shanghai Chenhua Instrument Co. China). 2.2. The preparation of different NiO hollow microspheres Synthesis of carbon spheres: Sucrose (13.861g) was dissolved in distilled water (135ml), and stirred with a magnetic stirrer to give a clear solution in a beaker. Then the solution was transferred into Teflon autoclaves, sealed and maintained at 180℃ for 10 h. The precipitate was collected by centrifugation, washed with distilled water and ethanol several times after it cooled to room temperature naturally. At last, it was dried at 80℃ for 6h, and the dark-brown block product was obtained. Synthesis of Ni(OH)2/C precursors:

ACCEPTED MANUSCRIPT Carbon spheres (0.144g) and NiCl2•6H2O (0.0952g) were dispersed in 80 ml distilled water by ultrasonicating for 0.5 h and stirring for 0.5 h to ensure that Ni2+

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ions can be sufficiently adsorbed on the surface of carbon balls. Then urea (0.5g) was

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added and kept stirring for 0.5 h. After that, the solution was transferred into a Teflon

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autoclave and kept at 90℃ for 8 h. The obtained suspension was cooled to room temperature and centrifuged to obtain the Ni(OH)2/C precursor. The as-obtained

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product was washed several times with distilled water, and dried at 80℃.

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Synthesis of different NiO hollow microspheres:

The Ni(OH)2/C precursor was put into the sequencing tube furnace and heated to

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550℃ with air drummed into at the rate of 7℃ per minute, and kept at 550℃ for 2 h.

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Then the furnace was gradually cooled to room temperature. By adjusting the final

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temperature, the NiO-HMs at 350℃/450℃/650℃ is separately obtained. 2.3. Electrochemical testing The working electrode was prepared as follows: The NiO-HMs samples (5 mg) were dissolved in a mixture of 20 µL Nafion and 5 mL absolute ethanol. A suspension was obtained under ultrasonic agitation for a few minutes. Then 20 µL of the mixture was dropped onto the cleaned GCE and dried at 50℃ in oven. All experiments were conducted using a three-electrode electrochemical system with a GCE based working electrode, an Ag/AgCl reference electrode and a platinum slice counter electrode. NaOH (0.1M) as electrolyte were deoxygenated with highly pure nitrogen for at least 15 min before measurements. Cyclic voltammograms (CVs) were recorded between 0 and 0.8 V at different scanning rate of 20-80 mV/s. The ampeometric response of the

ACCEPTED MANUSCRIPT NiO-HMs to the glucose was carried out at an applied potential of 0.5 V with the scanning rate of 50 mV/s, and 5mM glucose was added into electrolyte within 1100

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seconds by pipette, with respective volume of 10µL, 20µL, 50µL, and 100µL. The

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measurement was carried out with N2 continuously bubbling in the solution so as to

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remove the dissolved oxygen and to assure that the solution was well-stirred.

3.1. Characterization and analysis

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3. Results and discussion

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The morphology of the NiO hollow microspheres was observed with scanning electron microscopy. SEM images of NiO-HMs at 350℃/450℃/550℃/650℃

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(NiO-HMs-350/450/550/650) are respectively showed in Fig. 1(a)-(d). It can be seen

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that all the NiO microspheres fabricated by the nanoplates appear as flower-like. At

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lower temperature, some NiO nanoparticles scatter outside and can’t assemble well. With the increase of temperature, flower-like microspheres gradually reunite regularly in Fig. 1(c), and then reunite into spherical bulk at 650℃ with the longer diameter of 2µm. In addition, Fig. 1(e) displayed the partial of the NiO-HM-550 after the internal carbon sphere was burn and disappeared, which clearly proves the hollow structure. The chemical composition of NiO-HMs was confirmed by EDX technique, as exhibited in Fig. 1(f), showing the presence of the Ni and O elements. SEM sprays platinum in operation, which is why the EDX pattern shows the existence of Pt element. Fig. 2(a) shows the TEM of NiO hollow microsphere at 550℃. It can be clearly investigated that the substructures of nanoplates in the flower-like microspheres are

ACCEPTED MANUSCRIPT constructed of many NiO nanoparticles with the length of about 12.5nm and the width of about 10nm. The high-resolution TEM image is shown in Fig. 2(b). The lattice

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fringe can easily be observed, and the lattice spacing (0.21 nm) agrees with NiO (200)

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plane spacing from Figure 2(c). Taking the SEM and TEM images into account, we

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can infer that the hierarchical structure of the flower-like NiO hollow microspheres consisted of two levels: the micrometer sized nanoplates and the elementary

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nanocrystals. The diffraction rings shown in SAED image (Fig. 2c) can be indexed to

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(111), (200), (220), (311) and (222) diffraction of face-centered cubic NiO, respectively which explains that the prepared NiO architectures were polycrystalline.

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The X-ray diffraction (XRD) is mainly used for analyzing the composition and

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phase structure of the products. Fig. 3 shows the XRD pattern of the

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NiO-HMs-350/450/550/650. The four samples respectively exhibit five strong well defined diffraction peaks at 2θ of 37.12, 43.16, 62.77, 75.30 and 79.29º, which are attributed to (111), (200), (220), (311), (222) planes of face-centered cubic NiO phase[26-28]. That is consistent with the results of SAED. The intensity of the NiO-HMs peaks is gradually increasing from 350℃ to 550℃, which indicates the crystallinity is stronger and stronger with the progressive precipitation of the samples. That is associated with morphology changes. Two little peak in Fig. 3a and b can be seen, that are Ni (111) and Ni (200). If the temperature is higher, carbon spheres are rapidly oxidated into CO2, but the Ni(OH)2 reduces into Ni at lower temperature with the carbon sphere as reductive agent. Fig. 4 presents the TG/DSC curves of Ni(OH)2/C precursor at 50℃-700℃. It can

ACCEPTED MANUSCRIPT be seen from the TG curve that the composite of Ni(OH)2 and carbon sphere firstly loses the adsorbed water during the temperature programming. From 50℃ to 150℃,

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the weight cuts off 3.5%. Secondly, when the temperature arrives to 350℃, the

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composite almost finishes the dehydroxylation reaction: Ni(OH)2→ NiO + H2O,

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accompanied with part of carbon damages. The thermal decomposition reaction results in 11.3% weight loss. With the increase of temperature, the third

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weightlessness is happened, but can’t reach a steady state at 450℃. From 350℃ to

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550℃, the weight loss totals 25.6% and mainly finishes. Oxygen-containing functional group on the amorphous carbon of anhydrous NiO/C microsphere

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decomposes and appears a large number of carbide losses [29]. The Ni(OH)2/C

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completely reacts into NiO with the best crystallization at 550℃. That is in line with

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the XRD results. The thermal compensation of power displayed in DSC curve shows obvious peak of absorptive and exothermic process, which proves the existence of dehydroxylation and oxidation reaction. Therefore, the formation of hierarchical flower-like NiO hollow microspheres may be illustrated as shown in scheme 1. The carbon spheres were used as the template in the process. Firstly, the negatively charged surface functional groups of carbon spheres attract Ni2+ in NiCl2 solution through adsorption. Then, urea was added in above solution and hydrolyzed to slowly release OH- under heating at 90℃, the OH- reacted with Ni2+ to generate Ni(OH)2. Finally, the precursor was calcined to NiO at different temperature under air atmosphere and the carbon sphere can be completely oxidized and removed to form the hollow NiO microsphere.

ACCEPTED MANUSCRIPT 3.2 Electrochemical behaviors of glucose at different NiO-HMs/GCE Fig. 5 (a) gives voltammetric curves of the NiO-HMs-550/GCE electrodes in the

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absence and presence of glucose in NaOH solution. As shown in figure 5a well

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defined quasi-reversible redox peaks were observed for NiO-HMs-550/GCE

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electrodes with anodic peak potential at about 0.53 V and the cathodic peak at about 0.41 V in absence of glucose. These two peaks are assigned to Ni2+/Ni3+ redox couple.

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Upon addition of 2.5 mM glucose, the anodic peak currents of the electrodes are

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enhanced greatly, which is due to the change in the Ni2+/Ni3+ concentration ratio as a result of the rapid electrocatalytic oxidation of glucose, the mechanism for which is as

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NiO + H2O→ Ni(OH)2

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follows:[30-32]

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Ni(OH)2 + OH− ⇔ NiO(OH) + H2O + eNiO(OH) + glucose → Ni(OH)2 + glucolactone

(1) (2) (3)

During cyclic voltammetric measurement, the NiO-HMs may be firstly oxidized to NiO(OH) in NaOH solution as depicted in equations (1) and (2), and then the glucose was oxidized by NiO(OH), which resulted in the regeneration of Ni(OH)2. As a result, the change in concentrations of Ni2+ and Ni3+ species cause the increase in the anodic peak current and decrease of the cathodic peak current. The change in redox peak current density after glucose addition is believed to be due to the fact that the Ni2+/Ni3+ redox couple serves a double function of the electronic medium and catalyst, synchronously.

ACCEPTED MANUSCRIPT The NiO-HMs-350/450/550/650 was applied to modify the GCE for studying the electrochemical property. Fig. 5(b) shows the CV curves of the electrodes in 2.5 mM

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glucose at the scan rate of 50mV/s. It can be obviously seen that the

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NiO-HMs-550/GCE has the highest peak current, which demonstrates that NiO-HMs

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with appropriate density and crystalline can serve as the best glucose sensor. The reason for the better response to glucose oxidation of the hollow NiO-550 ºC may be

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speculated from its synergetic effect of morphology and crystallinity. As can be

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investigated from the SEM images the spherical structure can be formed at 350 ºC at which temperature the carbon sphere template may not be completely removed.

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Moreover, the crystallinity was also a little lower at the low temperature. With

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increase of the temperature the hollow structure may be eventually obtained. However,

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when the temperature was increased to 650 ºC it can be seen from the SEM image that the shrinks and collapse occurred at the surface of the spherical structure which may influence the surface structure and specific surface area of the catalyst and ultimately affected the electrochemical activity. Therefore the special hierarchical flower-like structure of NiO hollow microspheres may expose the larger specific surface area of catalyst and induce the higher performace of the electrochemical activities. The similar results were also obtained on other structured nickel oxide hollow microsphere [28]. The electrocatalytic activity of NiO-HMs-550/GCE towards glucose oxidation was further investigated by CV at a scan rate of 50 mV s-1 (Fig. 6a). The anodic peak current evidently increases with the addition of glucose and the enhancement is more

ACCEPTED MANUSCRIPT obvious. This phenomenon implies that the NiO-HMs-550/GCE has good electrocatalytic behavior in glucose oxidation. Fig. 6(b) gives the CVs of

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NiO-HMs-550/GCE at different scan rate in 5 mM glucose. Obviously, the peak

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potential for the catalytic oxidation of glucose shifts to positive values with increasing

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scan rate. Moreover, the peak current densities for the oxidation are proportional to the square root of the scan rate, as depicted in the illustration of Fig. 6 (b), indicating

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the electrochemical reaction on the surface of the NiO-HMs/GCE is a

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diffusion-controlled process.

3.3 The glucose sensing properties of the different NiO-HMs 7

shows

typical

chronoamperometric

(CA)

response

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different

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Fig.

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NiO-HMs/GCE to the successive addition of glucose at an applied potential of 0.5 V.

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As shown in Fig. 7, the NiO-HMs-550/GCE shows the largest current response to glucose oxidation (green line), compared with the other NiO-HMs/GCE. Apparently, the catalytic performance of NiO-HMs-550/GCE is better than that of other NiO-HMs/GCE, which is consistent with the result of the cyclic voltammograms. The typical amperometric responses of the NiO-HMs-550/GCE to the successive step-wise addition of glucose can be divided into two sections. Fig. 8 shows linear calibration of NiO-HMs-550/GCE between the current response and glucose concentration which are measured from chronoamperometric experiment. The average value of response after each addition is selected to quantify the glucose. It clearly indicates that the current value firstly rises sharply, then drops down [7, 13, 16, 26, 28]. When conducting the linear calibration, we find that the range of 8µM-364µM

ACCEPTED MANUSCRIPT glucose with a sensitivity of 288.87 mA mM-1 cm-2 and a correlation of 0.991 is corresponding to the lower part. And another higher linear range is 2.96mM-7.46mM

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glucose with a sensitivity of 37.82mA mM-1 cm-2 and a correlation of 0.99. The

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sensitivity of the NiO-HMs-550 sensor is divided the slope of the linear regression

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equation by the electrode surface area. Its sensitivity is higher than that of the other similar glucose sensors [13-14, 16-17, 33-36], as shown in Table 1. Based on a

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signal-to-noise ration of 3 (S/N), a low detection limit of 2µM can be obtained.

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3.4. The study of interference and stability

The selectivity and stability of the sensors are important but also challenging

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aspects to glucose sensor. In practice, there are some general distracters impacting the

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performance of glucose sensor, such as amino acid, ascorbic acid and urea detection.

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So it is important to research the interfering substances of NiO-HMs-550 sensor. Fig. 9 shows the current response when adding 0.5mM glucose, 0.05mM urea, 0.05mM ascorbic acid, 0.05mM L-leucine, 0.5mM NaCl, 0.05mM L-proline and 0.05mM L-lysine. According to the physiological glucose concentration (4-7mM), the interfering substances are thought to have no effect on the glucose sensing system. The current response have no obvious difference after the electrode was put aside for three days, which suggested that the glucose sensor of the NiO-HMs system has the good stability and anti-interference.

4. Conclusions In this work, NiO hollow microspheres obtained at different temperature have been assembled using carbon sphere as template via a hydrothermal method. The

ACCEPTED MANUSCRIPT hierarchical flower-like NiO-HMs at 550℃ consisted of two levels: the micrometer sized nanoplates and the elementary nanocrystals with the length of about 12.5nm and

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the width of about 10nm. The results of electrochemical test indicate the

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NiO-HMs-550/GCE has the best glucose sensing performance which exhibits high

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sensitivity of 288.87mA mM-1 cm-2 and with the linear wide 8µM-364µM. And the constructed NiO-HMs-550 sensor is also used into detection of glucose with the linear

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concentration range of 2.96mM-7.46mM and sensitivity of 37.82mA mM-1 cm-2.

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Importantly, the sensitivity of the NiO-HMs-550 non-enzymatic glucose sensor is

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improved highly compared with the other sensors.

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Acknowledgment

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Financial support for this work from National Natural Science Foundation of China (No. 41271249) and Key Laboratory of Advanced Textile Materials and Manufacturing Technology (Zhejiang Sci-Tech University), Ministry of Education (No. 2013008)

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ACCEPTED MANUSCRIPT Synthesis and formation mechanism of flowerlike architectures assembled from ultrathin NiO nanoflakes and their adsorption to malachite green and acid red in water, Chemical Engineering Journal. 239 (2014) 141–148.

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[33] P. Lu, J. Yu, Y.T. Lei, S.J. Lu, C.H. Wang, D.X. Liu, Q.C. Guo, Synthesis and

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characterization of nickel oxide hollow spheres–reduced graphene oxide–nafion composite and its biosensing for glucose, Sensors and Actuators B. 208 (2015) 90-98.

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[34] W.D. Zhang, J. Chen, L.C. Jiang, Y.X. Yu, J.Q. Zhang, A highly sensitive

Microchim Acta. 168 (2010) 259-265.

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nonenzymatic glucose sensor based on NiO-modified multi-walled carbon nanotubes,

[35] L.Q. Luo, F. Li, L.M. Zhu, Y.P. Ding, Z. Zhang, D.M. Deng, B. Lu,

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Nonenzymatic glucose sensor based on nickel(II)oxide/ordered mesoporous carbon modified glassy carbon electrode, Colloids and Surfaces B: Biointerfaces. 102 (2013)

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307-311.

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[36] E. Sharifi, A. Salimi, E. Shams, A. Noorbakhsh, M.K. Amini, Shape-dependent electron transfer kinetics and catalytic activity of NiO nanoparticles immobilized onto

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DNA modified electrode: Fabrication of highly sensitive enzymeless glucose sensor, Biosensors and Bioelectronics. 56 (2014) 313-319.

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Fig.1 (a)-(d) SEM imagines of the NiO hollow microspheres at 350℃/450℃/550℃

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/650℃; (e) the partial photo and (f) EDX pattern of NiO-HMs-550

550℃

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Fig. 2 (a) TEM, (b) HRTEM, (c) SAED patterns of the NiO hollow microsphere at

Fig. 3 XRD pattern of NiO hollow microspheres (a-d: NiO-HMs-350/450/550/650)

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Fig. 4 TG/DSC curves of C/Ni(OH)2 precursor

Scheme 1 Illustration of the formation of NiO hollow microspheres

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Fig. 5 Cyclic voltammogram of (a) the NiO-HMs-550/GCE in NaOH and 2.5mM glucose solution; (b)the different NiO-HMs/GCE in 2.5mM glucose solution

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Fig. 6 (a) CVs of NiO-HMs-550/GCE with different glucose concentration at a scan

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rate of 50mV/s; (b) CVs of NiO-HMs-550/GCE with 5mM glucose at different scan rate; insert is relationship between peak current and the square root of scan rate

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Fig. 7 Amperometric response of NiO-HMs-350/450/550/650 sensors with successive addition of glucose

Fig. 8 Linear calibration between the current response and glucose concentration in the range of 8µM-364µM glucose and 2.96mM-7.46mM glucose Fig. 9 Interference test of NiO-HMs-550 glucose sensor Table 1

Comparison of analytical performance of NiO-HMs-550 glucose sensor with other published non-enzymatic glucose sensors

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(b)

(d)

(f)

Ni

(e)

Ni Counts/cps

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(c)

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Pt O Ni

Pt 0

Pt 2

4 6 Energy/KeV

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Fig. 1 (a)-(d) SEM imagines of the NiO hollow microspheres at 350℃/450℃/550℃ /650℃; (e) the partial photo and (f) EDX pattern of NiO-HMs-550

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(a) (b)

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0.21nm

(c)

( 111) ( 200) ( 220) ( 311) ( 222)

Fig. 2 (a) TEM, (b) HRTEM, (c) SAED patterns of the NiO hollow microsphere at 550℃

(200)

(220)

d (311)(222)

c

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Intensity/a.u.

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(111)

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Ni(111) Ni(200)

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b a

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2θ/°

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Fig. 3 XRD pattern of NiO hollow microspheres (a-d: NiO-HMs-350/450/550/650)

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25.6%

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DSC value/mW 100 TG value/%

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Fig.4 TG/DSC curves of C/Ni(OH)2 precursor

Mass loss/%

3.5%

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Compensation power/mW

-20

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Agitation

Hydrothermal

Calcination

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Carbonization

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(Sucrose)

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Carbon sphere

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NiCl2•6H2O Ni2+ ions

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Urea Ni(OH)2

NiO

Scheme 1 Illustration of the formation of NiO hollow microspheres

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in NaOH in 2.5mM glucose

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0.2 0.1

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Current/mΑ

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0.4 Potential/V

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0.8

Current/mΑ

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hollow NiO-350°C hollow NiO-450°C hollow NiO-550°C hollow NiO-650°C

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0.1

0.0 0.0

0.2

0.4 Potential/V

0.6

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Fig. 5 Cyclic voltammogram of (a) the NiO-HMs-550/GCE in NaOH and 2.5mM glucose solution; (b)the different NiO-HMs/GCE in 2.5mM glucose solution

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(a)

0.6

2.5mM glucose

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Current/mΑ

20mM glucose

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0.4 Potential/V

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(b) Current/mA

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oxidation peak

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5

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1/2

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ν /mV⋅s

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80 mV/s 20 mV/s

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0.2

0.4 0.6 Potential/V

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Fig. 6 (a) CVs of NiO-HMs-550/GCE with different glucose concentration at a scan rate of 50mV/s; (b) CVs of NiO-HMs-550/GCE with 5mM glucose at different scan rate; insert is relationship between peak current and the square root of scan rate

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0.03

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hollow NiO-350°C hollow NiO-450°C hollow NiO-550°C hollow NiO-650°C

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164µΜ

74µΜ

34µΜ

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364µΜ

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600 Time/s

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Fig. 7 Amperometric response of NiO-HMs-350/450/550/650 sensors with successive addition of glucose

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7.46mM

60

2.96mM

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Fig. 8 Linear calibration between the current response and glucose concentration in the range of 8µM-364µM glucose and 2.96mM-7.46mM glucose

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0.5mM glucose

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0.5mM glucose

0.05mM L-lysine

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0.5mM NaCl 0.05mM L-leucine 0.05mM L-proline

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Fig. 9 Interference test of NiO-HMs-550 glucose sensor

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Table 1

Comparison of analytical performance of NiO-HMs-550 glucose sensor with other

Linear range(µM)

Ni/Cu/MWCNT CuO/SWCNT NiNPs/SMWNTs NiO/Pt/ERGO NiOHSs-RGO-NF NiO/MWCNTs NiO/OMC NiONPs/DNA NiO-HMs-550

0.025-800, 2000-8000 0.05-1800 1-1000 50-5660 0.6246-10500 ~7000 2-1000 1000-20000

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Type of electrodes

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published non-enzymatic glucose sensors

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5-364, 2960-7460

Sensitivity(µA mM-1 cm-2)

References

2633, 2437 1610 186.95 668.2 2721 1770 834.8 17320 288870, 37820

[13] [14] [16] [17] [33] [34] [35] [36] This work