title: 'Chocolate' silver nanoparticles: Synthesis, antibacterial activity and cytotoxicity.
abstract: OBJECTIVE
  Silver nanoparticles (AgNPs) have emerged as a powerful weapon against antibiotic resistant microorganisms. However, most conventional AgNPs syntheses require the use of hazardous chemicals and generate toxic organic waste. Hence, in recent year's, plant derived and biomolecule based synthetics have has gained much attention. Cacao has been used for years for its medicinal benefits and contains a powerful reducing agent - oxalic acid. We hypothesized that, due to the presence of oxalic acid, cacao extract is capable of reducing silver nitrate (AgNO3) to produce AgNPs.
  
  
  METHODS
  In this study, AgNPs were synthesized by using natural cacao extract as a reducing and stabilizing agent. The reaction temperature, time and reactant molarity were varied to optimize the synthesis yield.
  
  
  RESULTS
  UV-visible spectroscopy (UV-vis), dynamic light scattering (DLS) and transmission electron microscopy (TEM) characterization demonstrated that the synthesized AgNPs were spherical particles ranging in size from 35 to 42.5nm. The synthesized AgNPs showed significant antibacterial activity against clinically relevant pathogens such as Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Staphylococcus epidermidis. Importantly, these green AgNPs are not cytotoxic to human dermal fibroblasts (HDFs) at concentrations below 32μg/ml. We conclude that cacao-based synthesis is a reproducible and sustainable method for the generation of stable antimicrobial silver nanoparticles with low cytotoxicity to human cells. The AgNPs synthesized in this work have promising properties for applications in the biomedical field.
authors: School of Engineering, University of South Australia, Mawson Lakes, SA 5095, Australia. Electronic address: neelika.roy_chowdhury@mymail.unisa.edu.au.
authors: Neelika Roy
authors: NR
authors: Chowdhury
authors: Future Industries Institute, University of South Australia, Mawson Lakes, SA 5095, Australia. Electronic address: Melanie.Ramiasa@unisa.edu.au.
authors: Melanie
authors: M
authors: MacGregor-Ramiasa
authors: Microbiology Laboratory, The School of Dentistry, The University of Adelaide, Adelaide, SA 5005, Australia. Electronic address: peter.zilm@adelaide.edu.au.
authors: Peter
authors: P
authors: Zilm
authors: School of Engineering, University of South Australia, Mawson Lakes, SA 5095, Australia. Electronic address: Peter.Majewski@unisa.edu.au.
authors: Peter
authors: P
authors: Majewski
authors: School of Engineering, University of South Australia, Mawson Lakes, SA 5095, Australia. Electronic address: Krasimir.vasilev@unisa.edu.au.
authors: Krasimir
authors: K
authors: Vasilev
mesh_terms: D000900:Anti-Bacterial Agents / Q000138:chemical synthesis* / Q000494:pharmacology; D002099:Cacao / Q000737:chemistry*; D002470:Cell Survival / Q000187:drug effects; D020405:Dermis / Q000166:cytology / Q000187:drug effects; D004926:Escherichia coli / Q000187:drug effects / Q000254:growth & development; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects; D006801:Humans; D053768:Metal Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D008826:Microbial Sensitivity Tests; D019815:Oxalic Acid / Q000737:chemistry*; D010316:Particle Size; D010936:Plant Extracts / Q000737:chemistry; D061251:Primary Cell Culture; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000254:growth & development; D012834:Silver / Q000737:chemistry* / Q000494:pharmacology; D012835:Silver Nitrate / Q000737:chemistry; D013211:Staphylococcus aureus / Q000187:drug effects / Q000254:growth & development; D013212:Staphylococcus epidermidis / Q000187:drug effects / Q000254:growth & development
chemical_list: D000900:Anti-Bacterial Agents; D010936:Plant Extracts; D012834:Silver; D012835:Silver Nitrate; D019815:Oxalic Acid
keywords: Antibiotic resistance; Antimicrobial; Cacao; Cytotoxicity; Pathogens; Silver nanoparticles