A Streptomyces strain isolated from the soil sediments of tropical freshwater wetlands in Malaysia demonstrated promising attributes to be developed into a versatile microbial nanofactory for the sustainable synthesis of ferric oxide nanoparticles (IONP). Process parameters such as temperature, ferric salt precursor concentration, cell free extract (CFE) concentration and biomass harvesting times are serious players in the extracellular generation of metallic nanoparticles. A statistical approach using One-Variable-At-A-Time (OVAT) Analysis followed by Response Surface Methodology (RSM) was employed towards the optimization of the microbial bioprocess and modulation of nanoparticle size dimensions. OVAT revealed that IONP production increased with increasing temperature, precursor concentration, harvesting time and CFE concentration with highest yield at 65 °C, 2 mM precursor concentration, 68 h harvesting time and 100% CFE concentration. A detailed statistical analysis using RSM (RSM) showed significantly strong negative interactive effects between temperature and CFE concentration (p = 0.0037), temperature and precursor concentration (p = 0.0093) and mild interactive effects between CFE and precursor concentration (p = 0.0301). Taking into account the interactive influence of these variables, numerical analysis using RSM proposed that for optimal generation of microbial mediated IONP, a CFE concentration of 55.58%, temperature of 55.75 °C and precursor concentration of 2.46 mM FeCl3.6H2O would be required.

BackgroundIron based ferromagnetic nanoparticles (IONP) have found a wide range of application in microelectronics, chemotherapeutic cell targeting, and as contrast enhancers in MRI. As such, the design of well-defined monodisperse IONPs is crucial to ensure effectiveness in these applications. Although these nanostructures are currently manufactured using chemical and physical processes, these methods are not environmentally conducive and weigh heavily on energy and outlays. Certain microorganisms have the innate ability to reduce metallic ions in aqueous solution and generate nano-sized IONP’s with narrow size distribution. Harnessing this potential is a way forward in constructing microbial nanofactories, capable of churning out high yields of well-defined IONP’s with physico-chemical characteristics on par with the synthetically produced ones.ResultsIn this work, we report the molecular characterization of an actinomycetes, isolated from tropical freshwater wetlands sediments, that demonstrated rapid aerobic extracellular reduction of ferric ions to generate iron based nanoparticles. Characterization of these nanoparticles was carried out using Field Emission Scanning Electron Microscope with energy dispersive X-ray spectroscopy (FESEM–EDX), Field Emission Transmission Electron Microscope (FETEM), Ultraviolet–Visible (UV–Vis) Spectrophotometer, dynamic light scattering (DLS) and Fourier transform infrared spectroscopy (FTIR). This process was carried out at room temperature and humidity and under aerobic conditions and could be developed as an environmental friendly, cost effective bioprocess for the production of IONP’s.ConclusionWhile it is undeniable that iron reducing microorganisms confer a largely untapped resource as potent nanofactories, these bioprocesses are largely anaerobic and hampered by the low reaction rates, highly stringent microbial cultural conditions and polydispersed nanostructures. In this work, the novel isolate demonstrated rapid, aerobic reduction of ferric ions in its extracellular matrix, resulting in IONPs of relatively narrow size distribution which are easily extracted and purified without the need for convoluted procedures. It is therefore hoped that this isolate could be potentially developed as an effective nanofactory in the future.

This paper reports the green synthesis of Copper Oxide nanoparticles (CuO NPs) using Aquilaria malaccensis (agarwood) leaf extract. The main objective of this study was to evaluate the potential of using A. malaccensis leaf extract as a biogenic medium to generate CuO NPs with antimicrobial potential. The procedure employed was to add 5 mM copper sulfate (CuSO4.5H2O) as the precursor to A. malaccensis leaf extract to study the generation of CuO NPs under different incubation conditions such as methods of crude extract preparation, precursor concentration and incubation temperature. The results demonstrated that the boiled leaf extract reacted with 5 mM CuSO4.5H2O at pH 6 and incubated under non-shaking conditions at 70 °C, resulting in a high rate of CuO NPs formation and depicting a UV absorbance peak of 430 nm. Green synthesized CuO NPs were characterized using field emission scanning electron microscopy (FESEM) and energydispersive X-ray spectroscopy (EDX), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and transmission electron microscopy (TEM). FESEM and TEM revealed that the nanoparticles are mainly spherical, ranging from 6 to 32 nm. Antimicrobial studies showed that 20 µL and 40 µL of 70 µg/µL CuO NPs displayed potent inhibition towards Gram-positive bacteria Bacillus subtilis, with the average zone of inhibition measuring 24.43 ± 0.10 mm and 27.31 ± 0.13 mm, respectively.