Covalent P=N Bonding and Non-Covalent Interactions of Anthraquinone Derivatives with Few-Layer Black Phosphorus to Improve the Electrochemical Properties of the Functionalized Material

Abstract

Few and monolayer black phosphorus is currently intensively resaearch due to its excellent mechanical, electrical and optical properties [1]. Its application in the area of biosensors is a result of low cytotoxic cell-viability effects and excellent cytocompatibility [2]. Phosphorene has much higher surface to volume ratio compared to graphene and transition metal dichalcogenides. “Puckered” lattice structure and direct and tunable band gap of phosphorene distinguish it from other 2 D materials. These properties are advantages in sensing applications [3]. The major hurdle for phosphorene in processing and application is its fast oxidation and degradation in ambient conditions. Simultaneous disposition of light, oxygen and water causes the aging process [4,5]. The covalent and noncovalent functionalization of 2D black phosphorus with organic molecular materials is a very common approach that is used to protect its surface from air degradation and also to tailor its electrical properties [3]. Anthraquinone derivatives such as 1,4-diamino-9,10-anthraquinone (1,4DA-9,10-AQ) have an extended π-electron system that can increase the strength of noncovalent attractions. Anthraquinone (AQ) is a redox active small organic molecule frequently utilized for electrochemical labeling of biomolecules or providence of additional charge storage capacity [6].In this study, we present an electrochemical performance of covalently and noncovalently functionalized few-layer black phophorus by 4-azidobenzoic acid [7] and anthraquinone derivatives, respectively. The few-layer back phosphorus were obtained by liquid phase exfoliation in the anhydrous N.N-dimethylformamide. Next, the resultant suspension was centrifuged to remove the residual un-exfoliated particles, yielding supernatant.We functionalized few-layer black phosphorus (FLBP) by direct bonding of the phosphorus atom bearing lone electron pair with nitrogen during reaction with 4-azidobenzoic acid, leading to the formation of P=N double bonds, which passivate the reactive FLBP effectively. A covalent combining few-layered black phosphorus (FLBP) with 4-azidobenzoic acid can function as a bridge between FLBP and biomolecules. The functionalized phosphorene (f-FLBP) results in the possibility of using it as a biosensor platform for the detection of Heamophillus Influenza - one of the most common bacteria that cause infections in humans [8].The detection of Haemophilus Influenzae was carried out by the electrochemical impedance spectroscopy (EIS) method. The changes of the charge transfer resistance were associated with the variation in bacteria protein concentration. The biosensor of bacteria has been prepared in several steps: phosphorene preparation, functionalization with 4-azidobenzoic acid, followed by coating with an antibody layer. The limit of detection achieved was 5.82 µg mL-1, while the Haemophilus Influenzae bacterial protein determination sensitivity was equal to 1.2763%µg-1 mL. The developed electrochemical biosensor displayed a wide linear range from 3.37∙10−6 to 3.37 µg mL−1 for the determination of Haemophilus Influenzae bacterial protein.Noncovalent functionalization of FLBP was performed by drop casting method on glassy carbon (GC) electrode. The GC electrode with FLBP on the surface was immersed in a methanol solution of 1,4DA-9,10-AQ for two hours. Next, the noncovalently functionalized FLBP with 1,4DA-9,10-AQ (f-FLBP) was washed distilled water and dried under vacuum. The electrochemical properties of f-FLBP electrode such as stability, potential window, dependence of electrochemical properties on pH, electron transfer were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. Additionally the electrodes were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy (XPS). The obtained non-covalently functionalized FLBP was used for electrochemical detection of ascorbic acid by differential pulse voltammetry. ACKNOWLEDGEMENTS This work was supported by the Polish National Science Centre [2016/22/E/ST7/00102]; and the National Centre for Science and Development [347324/12/NCBR/2017]. The DS funds of the Faculty of Electronics, Telecommunications and Informatics of the Gdansk University of Technology are also acknowledged.