A domestic pressure cooker mediated, facile autoclaving method for the synthesis of silver nanoparticles

As an alternative to an expensive hydrothermal reactor, in the current method a domestic pressure was used for the synthesis of silver nanoparticles (Ag NP) using tree gum, kondagogu as dual functional reductant and stabilizer by autoclaving. The formation of Ag NP was evaluated with colour transformation, UV-Visible spectroscopy (UV-Vis) and transmission electron microscopy. The formation of Ag NP by gum confirmed from the developed yellow coloration of the solution and the appearance of surface plasmon resonance peak at 408 nm in the UV-Vis. The produced NP were spherical, polydisperse, particle size ranged from 2.9-17.6 nm and the average particle size was 4.5 ± 3.1 nm. The developed method is useful for demonstration, gaining hands on experience and production of metal and metal oxide NP in resource limited small laboratories, rural colleges, startups etc.•Pressure cooker serves as an easily accessible, durable, inexpensive, electricity independent hydrothermal nanoparticle production vessel.•Autoclaving serves as a facile, ecofriendly, less energy consuming, one pot, green method with dual functional role of in situ nanoparticle synthesis and sterilization.•Production of intrinsically safe and sterile nanoparticles amenable for in vivo and in vitro biomedical applications.

Multifaceted activities of plant gum synthesised platinum nanoparticles: catalytic, peroxidase, PCR enhancing and antioxidant activities

A single pot, green method for platinum nanoparticles (Pt NP) production was devised with gum ghatti (Anogeissus latifolia). Analytical tools: ultraviolet-visible (UV-vis), dynamic light scattering, zeta potential, transmission electron microscope, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy were employed. Wide continuous UV-vis absorption and black solution colouration proved Pt NP formation. Face-centred cubic crystalline structure of NP was evidenced from XRD. NPs formed were nearly spherical with a mean particle size of 3 nm. NP demonstrated a myriad of properties including catalytic, peroxidase, polymerase chain reaction (PCR) enhancing and antioxidant activities. Catalytic action of NP was probed via NaBH4 reduction of arsenazo-III dye. NP displayed considerable peroxidase activity via catalysis of 3, 3', 5, 5'-tetramethylbenzidine oxidation by H2O2. NP showed exceptional stability towards varying pH (3-11), temperature (25-100°C), salt concentration (0-100 mM) and storage time duration (0-12 months). In comparison with horse radish peroxidase, its applicability as an artificial peroxidase is advantageous. NP caused a two-fold enhancement in PCR yield at 0.4 nM. Also showed significant 1', 1' diphenyl picryl-hydrazyle scavenging (80.1%) at 15 µg/mL. Author envisages that the biogenic Pt NP can be used in a range of biological and environmental applications.

Tree gum stabilised selenium nanoparticles: characterisation and antioxidant activity

Selenium nanoparticles (Se NPs) were synthesised using sodium borohydride as a reductant and gum kondagogu as a stabiliser. Plant gum serves as a renewable, non-toxic, non-immunogenic, biopolymer based feedstock. Role of gum on synthesis and mean particle size was studied using ultraviolet-visible spectroscopy and dynamic light scattering. NP generation was visualised with orange red colouration and NPs exhibited a surface plasmon resonance peak at 250 nm. Formed NPs were amorphous, polydisperse and spherical. NPs showed a bimodal distribution, size varied from 44.4 to 200 nm and mean particle size was 105.6 nm. NP solution exhibited a zeta potential of -39.9 mV, confirming the superior stability. In comparison to ionic Se, the gum capped Se NPs exhibited superior 1, 1-diphenyl-2-picrylhydrazyle and 2, 2-azinobis-(3-ethylbenzthinzoline-6-sulphonic acid) radial scavenging activities of 73.2 and 92.2%, respectively, at 25 µg/ml. Antibacterial potential of NPs was checked with well diffusion assay. NPs exhibited growth inhibition activity against Gram-positive bacteria only. Bacillus subtilis and Micrococcus luteus showed respective inhibition zones of 6.3 and 8.6 mm at 12 µg. Thus, the present study demonstrates the applicability of tree gum stabilised Se NPs as a potent antioxidant nutrition supplement at a much lower dose, in comparison with ionic Se.

Bacteriogenic synthesis of selenium nanoparticles by Escherichia coli ATCC 35218 and its structural characterisation

A biosynthetic method for the production of selenium nanoparticles under ambient temperature and pressure from sodium selenite was developed using Gram-negative bacterial strain Escherichia coli ATCC 35218. Bacteriogenic nanoparticles were methodologically characterized employing UV-vis, XRD, Raman spectroscopy, SEM, TEM, DLS and FTIR techniques. Generation of nanoparticles was visualized from the appearance of red colour in the selenite supplemented culture medium and broad absorption bands in the UV-vis. Biofabricated nanoparticles were spherical, polydisperse, ranged from 100-183 nm and the average particle size was about 155 nm. Based on selected-area electron diffraction, XRD patterns; and Raman spectroscopy the nanospheres were found to be amorphous. IR spectrum revealed the involvement of bacterial proteins in the reduction of selenite and stabilization of nanoparticles. Used bacterial strain demonstrated efficient selenite reduction capability which was evident from 89.2% of selenium removal within 72 h at a concentration of 1 mM. Observation noted in the current study highlight the importance of bacterial reduction in selenium nanoparticle generation which can be scaled up for commercial production. Also, the bacteriogenic, amorphous nanoparticles can also be used as nutritional supplements for humans since selenium nanoparticles of 5-200 nm are bioavailable and known to induce seleno enzymes involved in antioxidant defence.

Biomimetic synthesis of selenium nanoparticles by Pseudomonas aeruginosa ATCC 27853: An approach for conversion of selenite

A facile and green method for the reduction of selenite was developed using a Gram-negative bacterial strain Pseudomonas aeruginosa, under aerobic conditions. During the process of bacterial conversion, the elemental selenium nanoparticles were produced. These nanoparticles were systematically characterized using various analytical techniques including UV-visible spectroscopy, XRD, Raman spectroscopy, SEM, DLS, TEM and FTIR spectroscopy techniques. The generation of selenium nanoparticles was confirmed from the appearance of red colour in the culture broth and broad absorption peaks in the UV-vis. The synthesized nanoparticles were spherical, polydisperse, ranged from 47 to 165 nm and the average particle size was about 95.9 nm. The selected-area electron diffraction, XRD patterns; and Raman spectroscopy established the amorphous nature of the fabricated nanoparticles. The IR data demonstrated the bacterial protein mediated selenite reduction and capping of the produced nanoparticles. The selenium removal was assessed at different selenite concentrations using ICP-OES and the results showed that the tested bacterial strain exhibited significant selenite reduction activity. The results demonstrate the possible application of P. aeruginosa for bioremediation of waters polluted with toxic and soluble selenite. Moreover, the potential metal reduction capability of the bacterial strain can function as green method for aerobic generation of selenium nanospheres.

Antibacterial activity of biogenic silver nanoparticles synthesized with gum ghatti and gum olibanum: a comparative study

Presently, silver nanoparticles produced by biological methods have received considerable significance owing to the natural abundance of renewable, cost-effective and biodegradable materials, thus implementing the green chemistry principles. Compared with the nanoparticles synthesized using chemical methods, most biogenic silver nanoparticles are protein capped, which imparts stability and biocompatibility, and enhanced antibacterial activity. In this study, we compared the antibacterial effect of two biogenic silver nanoparticles produced with natural plant gums: gum ghatti and gum olibanum against Gram-negative and Gram-positive bacteria. Bacterial interaction with nanoparticles was probed both in planktonic and biofilm modes of growth; employing solid agar and liquid broth assays for inhibition zone, antibiofilm activity, inhibition of growth kinetics, leakage of intracellular contents, membrane permeabilization and reactive oxygen species production. In addition, cytotoxicity of the biogenic nanoparticles was evaluated in HeLa cells, a human carcinoma cell line. Antibacterial activity and cytotoxicity of the silver nanoparticles synthesized with gum ghatti (Ag NP-GT) was greater than that produced with gum olibanum (Ag NP-OB). This could be attributed to the smaller size (5.7 nm), monodispersity and zeta potential of the Ag NP-GT. The study suggests that Ag NP-GT can be employed as a cytotoxic bactericidal agent, whereas Ag NP-OB (7.5 nm) as a biocompatible bactericidal agent.

Size-controlled green synthesis of silver nanoparticles mediated by gum ghatti (Anogeissus latifolia) and its biological activity

BACKGROUND

Gum ghatti is a proteinaceous edible, exudate tree gum of India and is also used in traditional medicine. A facile and ecofriendly green method has been developed for the synthesis of silver nanoparticles from silver nitrate using gum ghatti (Anogeissus latifolia) as a reducing and stabilizing agent. The influence of concentration of gum and reaction time on the synthesis of nanoparticles was studied. UV-visible spectroscopy, transmission electron microscopy and X-ray diffraction analytical techniques were used to characterize the synthesized nanoparticles.

RESULTS

By optimizing the reaction conditions, we could achieve nearly monodispersed and size controlled spherical nanoparticles of around 5.7 ± 0.2 nm. A possible mechanism involved in the reduction and stabilization of nanoparticles has been investigated using Fourier transform infrared spectroscopy and Raman spectroscopy.

CONCLUSIONS

The synthesized silver nanoparticles had significant antibacterial action on both the Gram classes of bacteria. As the silver nanoparticles are encapsulated with functional group rich gum, they can be easily integrated for various biological applications.

Biofouling and microbial corrosion problem in the thermo-fluid heat exchanger and cooling water system of a nuclear test reactor

This article discusses aspects of biofouling and corrosion in the thermo-fluid heat exchanger (TFHX) and in the cooling water system of a nuclear test reactor. During inspection, it was observed that >90% of the TFHX tube bundle was clogged with thick fouling deposits. Both X-ray diffraction and Mossbauer analyses of the fouling deposit demonstrated iron corrosion products. The exterior of the tubercle showed the presence of a calcium and magnesium carbonate mixture along with iron oxides. Raman spectroscopy analysis confirmed the presence of calcium carbonate scale in the calcite phase. The interior of the tubercle contained significant iron sulphide, magnetite and iron-oxy-hydroxide. A microbiological assay showed a considerable population of iron oxidizing bacteria and sulphate reducing bacteria (10(5) to 10(6) cfu g(-1) of deposit). As the temperature of the TFHX is in the range of 45-50 degrees C, the microbiota isolated/assayed from the fouling deposit are designated as thermo-tolerant bacteria. The mean corrosion rate of the CS coupons exposed online was approximately 2.0 mpy and the microbial counts of various corrosion causing bacteria were in the range 10(3) to 10(5) cfu ml(-1) in the cooling water and 10(6) to 10(8) cfu ml(-1) in the biofilm.