Antibiotic mediated synthesis of gold nanoparticles with potent antimicrobial activity and their application in antimicrobial coatings

Abstract

We report a one-pot synthesis of spherical gold nanoparticles (52-22 nm) and their capping with cefaclor, a second-generation antibiotic, without use of other chemicals. The differently sized gold nanoparticles were fabricated by controlling the rate of reduction of gold ions in aqueous solution by varying the reaction temperature (20-70 C). The primary amine group of cefaclor acted as both the reducing and capping agent for the synthesis of gold nanoparticles leaving the b-lactam ring of cefaclor available for activity against microbes. Antimicrobial testing showed that cefaclor reduced gold nanoparticles have potent antimicrobial activity against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria as compared to cefaclor or gold nanoparticles alone. The minimum inhibition concentrations (MICs) of cefaclor reduced gold nanoparticles were 10 mg mL À1and 100 mg mL À1 for S. aureus and E. coli respectively. The cefaclor reduced gold nanoparticles were further coated onto poly(ethyleneimine) (PEI) modified glass surfaces to obtain antimicrobial coatings suitable for biomedical applications and were tested against E. coli as an exemplar of activity. The antimicrobial coatings were very robust under adverse conditions (pH 3 and 10), inhibited the growth of E. coli on their surfaces, and could be used many times with retained activity. Results from a combined spectroscopic (FTIR) and microscopic study (AFM) suggest that the action of these novel particles is through the combined action of cefaclor inhibiting the synthesis of the peptidoglycan layer and gold nanoparticles generating ''holes'' in bacterial cell walls thereby increasing the permeability of the cell wall, resulting in the leakage of cell contents and eventually cell death.

Facile one-pot synthesis of amoxicillin-coated gold nanoparticles and their antimicrobial activity

“…We were able to control the particle size, the amount of drug loaded and the production time just by changing reaction temperature. Gold nanoparticles alone did not show any antibacterial property, and we were able to show that conjugation between the particles and the drug was necessary to enhance antibacterial activity against common gram-positive and gram-negative bacteria compared to cefaclor alone [16]. Moreover, we were able to coat a functionalised glass slide with cefaclor-reduced gold nanoparticles creating an antimicrobial film which was very robust and inhibited the growth of Escherichia coli on the surface over a range of pH conditions designed to mimic common cleaning scenarios [16].…”

“…The minimum inhibition concentration was calculated according to the method used by Sambhy et al [18] Results and discussion Amoxicillin-coated gold nanoparticles were prepared according to the one-pot synthesis of cefaclor-GNPs presented in our previous work [16]. In this case, the molar ratio of the reagents was varied, in part due to the lower water solubility of amoxicillin.…”

“…Aqueous solutions of amoxicillin (0.01 (not fully solubilised), 0.001 M) and HAuCl 4 (0.01 M) were prepared for use in the one-pot synthesis according to our previous work [16]. Materials were prepared at a range of gold/antibiotic molar ratios and temperatures (20-70°C).…”

“…The idea was to demonstrate that the one-step synthesis with cefaclor was not an isolated case, and that this approach, where the desired drug acts as reducing and capping agent, can be used to create a wide range of drugcoated GNPs. We identified various possible drug candidates that share some features with cefaclor, such as chemical structure and more importantly, the presence of a primary amine, which we demonstrated [16] to be at least partly responsible for the reducing/capping actions in the reaction. Different molecules from the cephalosporin and penicillin families, both β-lactam drugs, were investigated, and among them, amoxicillin, an antibiotic having poor water solubility, was chosen.…”

“…Recently, we reported a simpler water-based approach to antibiotic-coated gold particles [16] where cefaclor, a second generation antibiotic from the cephalosporin family, was shown to act as a reducing agent to produce the gold nanoparticles and, at the same time, coat them affording the desired anti-microbial nanomaterial, all in a single synthesis step. We were able to control the particle size, the amount of drug loaded and the production time just by changing reaction temperature.…”