# Biosynthesized Zinc Oxide Nanoparticles Disrupt Established Biofilms of Pathogenic Bacteria
## 1 Introduction  
Nanotechnology is an emerging field of science that deals with the application of nanomaterial in numerous fields [1]. In nanobiotechnology, the use of nanomaterials is mainly focused in medical diagnostics, drug delivery, agriculture, etc. [2]. The major interest in application of such nanomaterials is due to the fact that at nano scale, these materials exhibit a completely different set of properties encompassing physicochemical, optoelectronic, magnetic, etc. [3]. The very small size of nanoparticles makes their surface area to the volume ratio very large, making them drastically change their catalytic activity, mechanical properties, biological properties, electrical conductivity, etc. [4]. Hence, the researchers are focused on the development of nanomaterials capable of exhibiting novel properties that could be employed in various disciplines of medicine and biology. There are many commonly used methods of nanoparticles synthesis. Among them, chemical, physical, and biological methods are the most commonly used procedures [5]. In green synthesis, there is the use of natural products, such as plant extracts or microbes,to produce nanoparticles. The green route of nanoparticle synthesis is advantageous over chemical procedure due to the fact that chemical synthesis uses certain harmful materials and many times produces toxic byproducts [6; 7]. This makes the green route an eco-friendly procedure. Moreover, the green synthesis is usually a one-step process, produces relatively stable nanoparticles, and is also more economic than the chemical synthesis [8]. On the contrary, there are also certain drawbacks with the green route of nanoparticles synthesis. The major one is one is that nanoparticles produced in green synthesis are not of precise size and shape and are usually polydispersed in nature. Such variation is because the compounds of plants or microbes act as both reducing and stabilizing agent. There is simultaneous reduction, capping, and stabilization of nanoparticles that leads to the variations in shape and size of the particles. Moreover, the phytochemistry of plant extracts changes with the seasonal and climatic variations, making it a concern for the precise reproducibility of the physical and chemical properties of the synthesized nanoparticle [9]. In the recent past, there is tremendous rise in the number of antimicrobial-resistant (AMR) pathogens in environment, food, and clinical settings. The problem has become so serious in healthcare that the number of global deaths caused by the infectious diseases are next to cardiovascular ailments and cancer [10]. Drug-resistant pathogens not only create new infections, but also worsen the treatment of chronic diseases in which the therapeutic effectiveness of antibiotics is reduced [11; 12]. Moreover, if no proper action is taken, as per the speculations, the mortality caused by infectious diseases is expected to become the major reason for global deaths [13; 14]. Hence, the onset of multiple-drug resistance is not only challenging for the human health, but also for the environment and livestock. Biofilms are the microbial cells living inside the self-reduced matrix, mainly composed of natural plovers such as carbohydrates, proteins, DNA, etc. Biofilms are considered as hotspots and reservoirs for the antibiotic resistance genes [15]. The significance of biofilms can be predicted from the National Institute of Health (NIH) estimations which state that approximately 80% of infections are mainly supported by biofilms [16; 17]. Most of the studies conducted before 2000 in antimicrobial drug discovery only considered the planktonic mode of microbial growth; however, the vast majority of bacteria in the environment and at infection sites live in biofilm mode. This has led researchers working in antibacterial drug discovery to revisit their approach and also consider the biofilms as potential drug target. Certainly, there is a considerable gap in the development of newer antibiotics and the emergence of AMR.