ANTIMICROBIAL PROPERTIES OF DOPED AND UNDOPED PLANT- BASED SYNTHESIZED ZINC OXIDE AND SILVER NANOPARTICLES

CHAPTER ONE

1.0      INTRODUCTION

1.1       Background to the Study

The ongoing research in the realm of nanoparticles, is due to the unique properties its offer. Atoms are the major building blocks in living tissue, and are measured using the nanoscale.   Nano-sized particles allows interaction on molecules, this increases the efficacy and affinity when compared to biological molecules interacting with micro or macro sized particles (Li et al., 2008). The high surface area to core ratio, is a unique physical characteristic in nanoparticles that is there are more atoms on the surface of the nanoparticle than deep within its core. This is particularly useful since surface atoms have free surfaces in comparison to core atoms, with the ability to create new and strong bonds, in essence, nanoparticles are more reactive in comparison to micro and macro particle which have more core than surface atoms (Binns, 2010). In comparison to the same material in bulk, nano particles can be arranged easily in a number configurations due to their high surface to core ratio, making them easily manipulated and used in various applications. The greater l vibrations expressed by surface atoms in comparison to core atoms in any given material regardless of particle size, contribute to the lower melting temperature in nanomaterials compared to the same material inbulk (Buffat and Borel,  1976).  This  might  be  of  advantage  when  using  nanomaterials  to  construct porcelain fused to metal (PFM) crowns, cast post and cores, or denture frameworks. Nanoparticles  are  very  small  sized  particles  with  high  catalytic  reactivity,  thermal conductivity, non-linear optical performance and chemical steadiness owing to its large surface  area  to  volume  ratio.  Agarwal  et  al.  (2017).  Nanoparticles  have  s  being considered  as  nano  antibiotics  because  of  their  efficacy  in  antimicrobial  activities. Nanoparticles have been integrated into various industrial uses, like health, food, feed, space, chemical, and cosmetics industry of consumers this calls for a green and ecos- friendly approach to their synthesis Agarwal et al. (2017).

Two approaches have been suggested for nanoparticle synthesis: Bottom up and top down  approach.  The  top–down  approach  involves  millings  of  large  macroscopic particle. It involves synthesizing large-scale patterns initially and then reducing it to nanoscale  level  through  plastic  deformation  Agarwal  et  al.  (2017).  This  approach cannot be employed for large scale production of nanoparticles because it is costly and slow. Inter ferometric Litho- graphic (IL) is the most common technique which employs the role of top–down approach for nanomaterials synthesis. This technique involves the synthesis of nanoparticles from already miniaturized  atomic materials  through self- assembly. Agarwal et al. (2017). This includes formation through physical and chemical means.  It  is  a less  expensive  approach.  It  is  based  on  kinetic and  thermodynamic equilibrium approach. The kinetic approach involves MBE (Molecular Beam Epitaxy) Agarwal et al. (2017). Agarwal et al. (2017) study reveals that various inorganic metal oxides can be manufactured, such as tin oxide (TiO2), copper oxide (CuO), and zinc oxide (ZnO), among these three ZnO is more economical. US Food and Drug Administration (US FDA) identified ZnO as one of the good semiconductors because of its good band gap it can be used as cosmetic sunscreen lotions, anticancer, anti-diabetic, antibacterial, antifungal because of its UV filtering features. More so, ZnO is used to remove sulphur and arsenic from water, it also has protein adsorption properties, and can  also be applied in  dental surgery.  ZnONps have piezoelectric and  pyroelectric properties. They are used for disposal of aquatic weed which is resistant to all type of eradication techniques like physical, chemical and mechanical means.

ZnONPs  have  been  reported  in  different  morphologies  like  nano-flake, nanoflower,nano-belt, nano-rod and nano-wire. However, Silver nanoparticles (AgNPs) are increasingly used in various fields, including medical, food, health care, consumer, and industrial purposes, due to their unique physical and chemical properties. These include optical, electrical, and thermal, high electrical conductivity, and biological characteristics (Konrad et al., 2013). Due to their unique properties, they have been used for several applications, including as antibacterial agents, in industrial, household, and healthcare-related products, in consumer which includes food products and also, they are also used as  medical device coatings, optical sensors, and in cosmetics, in the pharmaceutical industry, in diagnostics, orthopedics, drug delivery, as anticancer agents, and have also help to improve the tumor-killing effects of anticancer drugs (Konrad et al., 2013).

1.2       Statement of the Research Problem

The emergence of bacterial resistance and multiresistance to antibiotics represent a major public health concern in Nigeria and in the entire world. Globally, antibiotic drug resistance causes an estimated 1 million death each year, if this continues, it is projected that by 2050-2060 antimicrobial resistance could result in over 10million deaths per year and over 200trillion USD will be lost globally. (WHO 2012, ACDC 2018). Antimicrobial materials used in the clinical setting today are beset by significant short falls including weak antimicrobial activities, difficulty in monitoring and extending the antimicrobial functions as well as difficulty in functioning in a dynamic environment (Martinez et al., 2010). Thus, effective and long term antibacterial and bio-film preventing materials constitute an immediate need in medicine.

Metals  and  non-metals  oxides  have  been  widely  studied  for  their  antimicrobial activities. However, most of the currently available methods or techniques for synthesizing these nanoparticles are expensive, environmentally harmful and inefficient with respect to material and energy use, this calls for a better and eco-friendly method for synthesizing nanoparticles.

1.3       Justification for the Research Problem

Senna occidentalis have been widely used for centuries by African, American and Indian tribes principally as a antimalarial or antimicrobial medicine, as a laxative or hepatoprotective  (Lombardo  et  al.,  2009).  Scientific data have revealed  that  Senna occidentalis comprise a rich source of phenolic derivatives with important biological and pharmacological properties (Ogunkunle et al., 2006). Senna occidentalis are readily available in sahara region and the sub-sahara regions.

Metals  and  non-metals  oxides  are  well  known for  their  highly potent  antibacterial effects. These include Silver (Ag), Zinc oxide (ZnO), Iron oxide (Fe3O4). Most metal oxide nanoparticles exhibit bacterial properties through reactive oxygen species (ROS) generation, although some are effective due to their physical structure and metal ion release.

Silver (Ag) and ZnO oxide finds a very promoient place in the field of doped nanoparticles in biomedical field. Silver (Ag) is a transition metal, which has properties like the electricial conductivity and reflectively of any metal. Kluel et al., 2000.

Zinc oxide (ZnO) is widely renowned for its antibacterial uses. The main reasons for this is the free electrons and positive holes which are generated when Zinc oxide, having a high band is bombarded with an energy equal or higher than this band gap energy. But this free energy electrons and holes recombined quite fast, not allowing them enough time to take part in any chemical reactions. So, the electrons and the holes should be captured by any material which exist on the surface (ions, molecules etc) or by some surface traps (Morales Flores et al., 2011). The doping comes as a solution to this problem and thus several researches have been done to enhance its activity by doping it with silver. Silver (Ag) and Zinc oxide precussors such as Silver nitrate (v) and Zinc acetate dehydrate are readily available and cheap.

In synthesizing this nanoparticles, the biosynthesis approach has been proposed as an alternative to reduce the usage of hazardous chemical compounds and harsh reaction conditions in the production of these nanoparticles.

Therefore,  this  research  work  focuses  on  using  aqueous  leaf  extract  of  Senna occidentalis to synthesize Ag,  ZnO nanoparticles and doped Silver and Zinc oxide nanoparticles and  to  evaluate their antimicrobial properties.

1.4       Aim and Objectives of the Study

The aim of this study is to evaluate plant-based-synthesis of Zinc oxide, silver nanoparticle and doped silver and zinc oxide nanoparticles along with their anti- microbial activities.

Specific Objectives are to;

i.      Determine  the  qualitative  phytochemical  constituents  of  Senna  Occidentalis using aqueous leaf extract.

ii.      Synthesize Zinc oxide (ZnO) and Silver (Ag) nanoparticles using aqueous leaf extract of Senna occidentalis by varying pH condition

iii.      Characterize  the  zinc  oxide  (ZnO)  and  silver  (Ag)  nanoparticles  using  UV visible spectroscope, Zeta sizer, transmission electron microscopy and frontier transformed infrared spectroscopy

iv.      Evaluate  the  antimicrobial  properties  of  silver,  zinc  and  doped  zinc/silver nanoparticles using microorganisms: Gram positive bacteria:  S. pyrogenes, S. aureus gram negative bacteria: S. aeruginosa and E. coli

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