Elsevier

Microelectronic Engineering

Volume 133, 5 February 2015, Pages 11-15
Microelectronic Engineering

Ordered-standing nickel hydroxide microchannel arrays: Synthesis and application for highly sensitive non-enzymatic glucose sensors

https://doi.org/10.1016/j.mee.2014.11.005Get rights and content

Highlights

  • This research may provide a meaning way in integratable sensors.

  • Si MCP itself is an excellent support for electrocatalyst.

  • The porous structure itself with high surface to volume ratio endows higher mass Ni(OH)2 nanopatricles.

  • The ordered channel and mesoporous structure permits liquid electrolyte flow easily.

Abstract

A non-enzymatic glucose sensor is constructed by using nickel hydroxide (Ni(OH)2) modified silicon microchannel plates (MCP) as the sensing materials. The 3D ordered Si MCP is fabricated by electrochemical etching and the Ni(OH)2 coating are prepared by electroless plating. The nanocomposite electrode exhibits good catalytic activity toward oxidation of glucose in 0.1 M KOH. This non-enzymatic glucose sensor boasts a fast amperometric response time of less than 5 s, sensitivity of 0.25 mA mM−1 cm−2, and detection limit of 3.5 μM at a signal-to-noise ratio of 3. The sensor shows superior stability, anti-interference capability, and selectivity. The good analytical capability, low cost, and compatibility with silicon technology make the Ni(OH)2/Si MCP electrode promising in amperometric non-enzymatic glucose detection.

Graphical abstract

The figure (a) depicts the top-view and cross-sectional SEM images of the electrochemically etched Si MCP with a large aspect ratio. The surface has a regular square morphology with all the channels aligned orderly. The etched microchannel depth reaches approximately 200 μm and the square holes are about 5 μm in length. The use of a structure with such a large vertical surface area to load the sensing materials is expected to increase the sensitivity of the sensor while maintaining the original small substrate footprint. After electroless nickel plating, nickel nano-grains several to hundreds of nanometers in size exist on the inner walls as the current collector layer of the sensor, as shown in (b). The surface of the nickel layer is not smooth and so it can provide more surface area to form nickel hydroxide. The morphology of the Ni(OH)2 film on the sidewall surface is depicted in (c). The morphology of the Ni(OH)2 film with the nano-flake morphology on the channels is not the same possibly due to the asymmetry of ion concentration deep inside the microchannels. The nano-flakes are intertwined to produce a nano-porous Ni(OH)2 film with a large surface area and short diffusion distance and excellent electrochemical performance is expected.

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Introduction

The development of novel glucose sensors with high sensitivity, reliability, fast response, and good selectivity is crucial to diagnosis and treatment of diabetes mellitus, clinical biochemistry, waste water treatment, and the food industry [1], [2], [3]. Since Clark and Lyons utilized glucose oxidase to produce the first enzymatic electrode in 1962 [4], it has attracted extensive attention. Conventional glucose sensors involve the use of glucose oxidase (GOD) which catalyzes oxidation of glucose in the presence of O2 to produce hydrogen peroxide. The signal transduction is based on oxidation of the hydrogen peroxide. Although this type of biosensors displays very high sensitivity and selectivity to glucose, the complicated immobilization procedures, thermal and chemical instability, and high cost of enzymes have hindered progress. Nevertheless, many types of enzymatic glucose sensors have aroused interest and been applied to direct electrochemical oxidation of glucose [5]. Some noble metals (Pt, Au, Ag, etc.), alloys (Pt–Pb, Pt–Au, Ni–Pd, etc.), metal oxides (RuO2, CoO, MnO2, etc.), carbon nanotubes, and graphene have been used in the fabrication of non-enzymatic glucose sensors [3], [6], [7], [8]. In particular, nickel-based nanomaterials exhibit remarkable activity owning the presence of the Ni(OH)2/NiOOH redox couple formed in an alkaline medium [9], [10]. Compared to the other materials, Ni is relatively economic. As known that nano/microstructured materials exhibit enhanced electrochemical performance and many types of Ni-based materials have been fabricated with various structures such as nanoparticles [11], [12], nanoflake arrays [13], and so on.

The use of Ni-based nanomaterials requires a supporting substrate. An ideal support should have the following properties: (1) high surface area for catalyst loading; (2) excellent conductivity and convenient routes for electron transfer; (3) compatibility with silicon technology to enable device miniaturization. Silicon microstructures such as Si microchannel plates (MCP) possess unique properties including ordered structure, biocompatibility, multi-functionality, and compatibility with microelectronics technology [14]. These advantages make Si MCPs promising in electrochemical sensors. In this work, a non-enzymatic glucose sensor based on Ni(OH)2/Si MCP electrodes is fabricated and the performance is studied systematically.

Section snippets

Materials and reagents

The wafer used to fabricate the Si MCPs was single-side polished, p-type silicon with a resistivity of 2–9 Ω cm, and a thickness of 525 μm. Hydrofluoric acid, dimethylformamide, ammonium fluoride, sodium hydroxide, ethanol, and all other reagents were of analytical reagent grade and used without purification. The specific resistivity (18 MΩ) of de-ionized water was used and all the experiments were carried out at room temperature in a clean environment.

Preparation of silicon microchannel plates

The silicon microchannel plates were

Formation of the Ni(OH)2/Si MCP electrode

Several studies have been devoted to the investigation of the electrochemical behavior of nickel electrodes in an alkaline solution and it has been shown that anodic oxidation of the nickel electrode in an alkaline solution involves the NiO/Ni(OH)2 and Ni(OH)2/NiOOH redox reactions [17], [18]. Hence, the nickel hydroxide coating is produced on the sidewall of the Si MCP by cyclic voltammetry (CV). The Ni(OH)2/Si MCP electrode is prepared in an aqueous solution of 0.1 M KOH at a scan rate of 50 mV s

Conclusion

A Ni(OH)2/Si MCP electrode prepared by electrochemical etching and electroless plating is applied to glucose sensing. The Ni(OH)2/Si MCP film consists of crystals with different morphologies on the inner walls of the microchannels. The Ni(OH)2/Si MCP electrode delivers excellent electrochemical performance in glucose oxidation including a fast response time of less than 5 s, low detection limit of 3.5 μM, linear detection of glucose in the concentration range between 0 and 8 mM, and high

Acknowledgements

This work was supported by the National Natural Science Foundation of China (Grant No. 61204127), Natural Science Foundation of Heilongjiang Province (Grant No. F201332), New Century Excellent Talents in Heilongjiang Provincial University (Grant No. 1253-NECT025), Guangdong – Hong Kong Technology Cooperation Funding Scheme (TCFS) No. GHP/015/12SZ, and City University of Hong Kong Applied Research Grant (ARG) No. 9667069.

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