Biogenic synthesis and characterization of gold nanoparticles using transformed mesophilic Escherichia coli BL21 and thermophilic Thermus thermophilus HB27

Abstract

Gold nanoparticles have numerous applications, many of which are notable in industries. The biosynthesis of gold nanoparticles offers an easy, effective, green, and eco-friendly approach. In organisms capable of synthesizing nanoparticles, enzymes and proteins are responsible for the structural and functional modifications that lead to their formation. These include ABC transporter, peptide-binding proteins, which are dependent on abiotic parameters. This study uses the purified ABC transporter, peptide-binding protein transformed from Thermus scotoductus SA-01 and expressed in mesophilic Escherichia coli BL21 and thermophilic Thermus thermophilus HB27 hosts for the biosynthesis of gold nanoparticles at different concentrations, temperatures, and pH values. Gold nanoparticle formation was evaluated with a range of gold (III) concentrations (0–10 mM), incubated at temperatures ranging from 30–85 ºC and pH levels from 3.6–9.0. Transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDX), and UV–Vis absorption spectroscopy were used to characterise the formation of nanoparticles. In all of the protein reactions, UV–Vis absorbance peaks at approximately 520–560 nm confirmed the formation of gold nanoparticles. Optimum nanoparticle synthesis was observed at pH values ranging from 5.5 to 9.0, gold (III) solution (HAuCl₄) concentrations from 0.5–2.0 mM, and a maximum temperature of 65ºC in the mesophilic host and 85ºC in the thermophilic host, indicating the significance of temperature in both hosts for the expression and bioactivity of the purified ABC transporter protein. However, the biogenic formation of gold nanoparticles using E. coli and T. thermophilus hosts was not monodispersed, suggesting a necessity for further development of the procedure.