Nanocopper-loaded Black phosphorus nanocomposites for efficient synergistic antibacterial application

https://doi.org/10.1016/j.jhazmat.2020.122317Get rights and content

Highlights

  • Novel nanocopper-loaded black phosphorus (BP/Cu) nanocomposites were synthesized.

  • The antibacterial effect is amplified after doped black phosphorus with nanocopper.

  • ROS burst was detected and the responsible ROS species were determined.

Abstract

Novel nanocopper-loaded black phosphorus (BP/Cu) nanocomposites were synthesized to synergistically exert enhanced antibacterial activities aimed at reducing antibiotics abuse. First, both BP and Cu display low biotoxicity, broadening their application in the microbiological field. Second, the unique electronic properties of BP enable BP/Cu nanocomposites to amplify antibacterial effects via interfacial charge transfer, resulting in a surge of reactive oxygen species (ROS). Third, BP/Cu nanocomposites are relatively stable, which helps to avoid the problem that nanocopper alone is highly oxidized. Finally, BP/Cu was synthesized in an environmentally-friendly manner by a one-step reduction method. The BP/Cu nanocomposites were characterized by transmission electron microscopy and atomic force microscopy. Their antibacterial properties were investigated comprehensively and discussed in detail by inhibition zone assays, dynamic growth curves, membrane potential assays, and live/dead baclight bacterial viability assays, all of which revealed the antimicrobial activities of BP/Cu nanocomposites. Absorption spectra were measured to determine which ROS species were responsible for the bactericidal mechanisms. In summary, our results demonstrated the potential of nanocomposites based on BP in antibacterial therapy due to its excellent electronic properties and outstanding biological performance. This will pave the way for avoiding antibiotic overuse and for providing security to humans and the environment.

Introduction

The advent of antibiotics has made a great contribution to human health, but unlimited overuse has led to the emergence of bacterial resistance, resulting in enormous harm, both to the environment and human beings. To solve those problems, research on various antibiotic alternatives antibiotics, including inorganic nanocomposites, polymers, and natural products has become a hot topic. (Sadeghi, 2018; Sun and Wu, 2018) Recently, the unique properties of black phosphorus (BP), a novel two-dimensional nanomaterial, have led to its application in several biological fields, including as antibacterial agent, in anticancer therapy, photoacoustic imaging, and in optoelectronic devices. (Shin et al., 2018; Zhou et al., 2019; Ding et al., 2018) As a new non-metallic 2D nanomaterial, the lattice of BP consists of six-membered rings that are linked to each other, and its performance and structures is much like graphite with metallic luster, flaky and conductivity (Li et al., 2019a; Hu et al., 2019). It is worth mentioning that the flaky structure of BP is not flat in a strict sense, but consists of a corrugated structure with a lone-pair electron on the outside. Hence, those individual properties equip BP with an effective interfacial charge transfer activity and an excellent carrier mobility, making it an excellent candidate for constructing metal-doped nanocomposites with superior performance (Favron et al., 2015; Liu et al., 2014; Jiang et al., 2016). In particular, BP displays excellent biocompatibility, because it can be degraded to phosphates or phosphate esters, which normally exist in organisms and which are inoffensive to normal tissues (Xiong et al., 2018; Li et al., 2019b). So far, BP is mainly used as a drug carrier and there are few studies on its antibacterial application (Wu et al., 2018; Shao et al., 2018; Wang et al., 2019a; Li et al., 2019c).

Inorganic antibacterial agents are considered to be good substitutes for antibiotics due to several advantages, including stability, broad-spectrum antibacterial activity and low drug resistance. Among these, silver-based antibacterial agents are typical representatives that are widely used. (Ouyang et al., 2018; Song et al., 2018; Wei et al., 2019; Wang et al., 2019b) However, the use of silver is associated with high costs, and the accumulation of silver in the body will eventually cause toxicity in humans. Therefore, copper has received great attention due to its low cost and its superior antibacterial property, especially in the case of nanocopper (Li et al., 2018; Halbus et al., 2019; Betts et al., 2018). Moreover, as one of the trace elements in the human body, copper shows lower biological toxicity than silver. Unfortunately, nanocopper is prone to rapid oxidization, which greatly limits its application. Nevertheless, research into novel copper-based composites, including their antimicrobial activity, their mechanisms of action, and their clinical applications, are facing more and more challenges. Exploring innovative nanocomposites which have been developed quickly in recent years, has become a research hotspot in the field of antimicrobial. (Li et al., 2019d; Gupta et al., 2019; Roy et al., 2019)

Based on these considerations and on recent research findings, we plan to synthesize a composite involving in black phosphorus and metal, to make full use of the high electronic activity of BP and the antibacterial properties of metal. Here, we report the synthesis of innovative nanocopper-loaded black phosphorus nanocomposites (BP/Cu), hypothesizing that the doped BP would significantly enhance the antimicrobial effectiveness of nanocopper owing to the interfacial charge transfer. Nanocopper is known for its excellent antibacterial properties, which is attributed to the nanometer-size effect and its high reactivity. BP is expected to be responsible for interfacial charge transfer with nanocopper due to its large surface area and its reactive lone-pair electrons, maximizing it antibacterial effect. In addition, the BP/Cu nanocomposites were obtained via an in-situ growth strategy by employing a simple, effective, environmental-friendly hydrothermal redox method. Finally, a series of experiments were carried out to verify the feasibility of this program.

Section snippets

Materials

Black phosphorus powder was obtained from XFNANO Advanced Materials Supplier (Nanjing, China). CuSO4·5H2O (analytical grade, 99 %), 1,3-diphenylisobenzofuran (DPBF, 97 %), N-phenyl-1-naphthylamine (NPN, 98 %) and polyvinylpyrrolidone (PVP, MW:1,300,000) were purchased from Aladdin. NaBH4 (reagent grade, 99 %) was obtained from Chengdu XiYa Chemical Technology Co. Ltd. The BacLight Bacterial Membrane Potential Kit (B34950), Singlet Oxygen Sensor Green (SOSG) Reagent and propidium iodide (PI)

Characterizations

The BP nanoparticles were prepared from bulk BP by liquid ultrasound exfoliation technique and the composites BP/Cu were obtained via in-situ growth strategy. As shown by the TEM images (Fig. 1a), the size of original bulk BP can be several hundred nanometers. However, after ultrasonic exfoliation, the obtained BP nanoparticles are only about 10 nm in size and display a relatively uniform distribution. The final BP/Cu nanocomposites exhibited a diameter of ∼50 nm with distinctive high contrast (

Conclusions

In this study, nanocopper-loaded BP nanocomposites BP/Cu were synthesized successfully via an in-situ growth strategy. Characterization of the nanocomposites by AFM and TEM showed that their sizes are suitable for touching and piercing membranes. More importantly, the BP/Cu nanocomposites did show an improved antibacterial property, owing to the ROS burst caused by the efficient synergistic effect between BP and Cu. The CLSM images with SYTO 9 and PI visually demonstrated that the BP/Cu

CRediT authorship contribution statement

Dandan Zhang: Conceptualization, Methodology, Writing - original draft. Hui Ming Liu: Investigation. XiuLin Shu: Resources, Investigation. Jin Feng: Software, Data curation. Ping Yang: Supervision. Peng Dong: Funding acquisition, Formal analysis. XiaoBao Xie: Project administration, Validation. QingShan Shi: Writing - review & editing, Project administration, Validation.

Declaration of Competing Interest

The authors declared that they have no conflicts of interest to this work.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (NO. 51802046), the Natural Science Foundation of Guangdong Province (2018A030313656), the Science and Technology Planning Project of Guangdong Province (No. 2016A010103020), the Science and Technology Program of Guangzhou, China (Grant 201804010145), and the GDAS' Special Project of Science and Technology Development (Grant 2018GDASCX-0912).

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