Electrochemical Biosensing of Food Allergens Using Vertically-Aligned Antibody Functionalized MXene
Authors: Ogata Yuta , Takimoto Daisuke , Hideshima Sho , Sugimoto Wataru 
Published: December 2020

Transition metal carbide nanosheets known as MXene possess electronic conductivity comparable to typical metallic materials.1 However, when fabricating MXene electrodes for electrochemical applications, due to the highly anisotropic nature of the nanosheet, MXene tends to re-stack and generally aligns horizontally with respect to the current collector. 2 Such electrodes suffer from low active surface area and slow kinetics owing to the poor diffusivity of the reactant. In this study, a vertically aligned MXene electrode is fabricated and used as a scaffold for electrochemical biosensing of allergenic protein in food. The vertically aligned MXene electrode can be anticipated to have enhanced electrolyte diffusivity transfer rate.
The vertically aligned MXene electrode was prepared by adopting the method developed to prepare vertically aligned graphene electrode.3 MXene was electrophoretically deposited from to an aqueous MXene colloid and subjected freeze-drying, and transferred to the surface of a glassy carbon (GC) electrode. The surface of MXene was modified as follows (Fig. 1A). The vertically aligned MXene electrode was immersed in 1 mM 3-aminopropyltriethoxysilane (APTES) solution, followed by the modification with the cross-linking reagents, N-(3-dimethylaminopropyl)-N’-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide. The antibody (provided by Nippon Flour Mills Co., Ltd.) was immobilized on the MXene surface, and bovine serum albumin (BSA) was used to prevent non-specific adsorption of non-related proteins. Electrochemical measurements of the antibody-immobilized electrode before and after the reaction with the allergenic protein were performed in phosphate buffered saline (PBS) solution containing 5 mM hexaaminerutenium (Ⅲ) chloride ([Ru(NH3)6]3+).
The thickness of vertically aligned MXene film according to scanning electron microscopy images was about 300 μm, and the distance between the walls of nanosheets was about 20 μm (Fig. 1B). From the surface image in Fig. 1C, the average pore diameter was about 20 µm, which was in good agreement with the distance between the walls of nanosheets. Subsequently, the electrochemical characteristics of the vertically- and horizontally-aligned MXene electrodes modified with antibody were evaluated by cyclic voltammetry (Fig. 1D). The vertically aligned electrode showed higher current density than horizontally-aligned electrode. In addition, a smaller difference between the oxidation potential and the reduction potential for the vertically aligned electrode. These results suggest an improvement in the diffusivity of the redox probe in the electrolyte.
Acknowledgments
We thank Prof. Yury Gogotsi and Dr. Babak Anasori (Drexel University) for providing MXene.
References

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Figure 1