Poonam Shokeen

Antidiabetic activity of 50% ethanolic extract of Ricinus communis and its purified fractions.

We investigated the antidiabetic activity of 50% ethanolic extract of roots of Ricinus communis (RCRE) along with its bioassay-guided purification. Five-hundred milligram per kilogram body weight appeared to be the effective dose as it caused the maximum lowering of the fasting blood glucose, both in normal as well as type 1 diabetic animals. The maximum hypoglycemic effect was always observed at the 8th h up to which the study has been conducted. Administration of the effective dose of RCRE to the diabetic rats for 20 days showed favorable effects not only on fasting blood glucose, but also on total lipid profile and liver and kidney functions on 10th and 20th day. RCRE was purified using silica gel column chromatography. Out of several different fractions tested, only one fraction (R-18) showed significant antihyperglycemic activity. RCRE seemed to have a high margin of safety as no mortality and no statistically significant difference in alkaline phosphatase, serum bilirubin, creatinine, serum glutamate oxaloacetate transaminase, serum glutamate pyruvate transaminase and total protein was observed even after the administration of the extract at a dose of 10 g/kg b.wt. Thus R. communis seems to have a promising value for the development of a potent phytomedicine for diabetes.

Preliminary studies on activity of Ocimum sanctum, Drynaria quercifolia, and Annona squamosa against Neisseria gonorrhoeae.

Background: Despite the progressive increase of antimicrobial resistance of Neisseria gonorrhoeae worldwide, there are limited reports of alternative remedies from plants. Goal: The aim of the current study was to screen 3 plants, Ocimum sanctum, Drynaria quercifolia, and Annona squamosa, for activity against Neisseria gonorrhoeae. Study: By disc diffusion method, extracts of these 3 plants were screened for activity against Neisseria gonorrhoeae; their antimicrobial activity was calculated as percentage inhibition and compared with penicillin and ciprofloxacin. Results: The extracts of all 3 plants caused inhibition of Neisseria gonorrhoeae clinical isolates and World Health Organization (WHO) strains, more so than the multidrug resistant Neisseria gonorrhoeae. Conclusion: Neisseria gonorrhoeae clinical isolates and WHO strains were sensitive to extracts of Ocimum sanctum, Drynaria quercifolia, and Annona squamosa. This motivates us to isolate the active component/second from the 3 plants.

In vitro activity of eugenol, an active component from Ocimum sanctum, against multiresistant and susceptible strains of Neisseria gonorrhoeae

In view of the widespread emergence of resistant isolates, an attempt was made to isolate and characterise the component(s) of Ocimum sanctum with activity against Neisseria gonorrhoeae. Bioassay-guided purification of the hexane extract of leaves of O. sanctum was carried out, which yielded H12c as the active compound. H12c was characterised and was determined to be eugenol, with a minimum inhibitory concentration of 85-256 mg/L. The antigonorrhoeal efficacy of H12c was better against multiresistant strains. The 50% lethal dose (LD50) of H12c was found to be 2g/kg body weight in rats. In view of its efficacy and lower toxicity, eugenol may be a potentially suitable molecule to be developed clinically in response to emerging resistant isolates of N. gonorrhoeae.

Evaluation of the activity of 16 medicinal plants against Neisseria gonorrhoeae

50% Ethanolic extracts of various parts of 16 medicinal plants were evaluated for potential activity against clinical isolates and WHO strains of Neisseria gonorrhoeae, including multidrug-resistant (MDR) strains. Activity was calculated as percentage inhibition in comparison with penicillin and ciprofloxacin and strains were categorised as less sensitive, sensitive or highly sensitive to the extracts. The extracts caused differential inhibition of N. gonorrhoeae, with greater inhibition of the MDR strains. Among the extracts tested, 60% exhibited high activity whereas 20% showed moderate activity and 20% had little activity against N. gonorrhoeae.

Enhanced performance of thin-film solar cell by metallic nanostructural vertical dual model

Abstract. Our present work proposes a systematic geometric model comprising vertical dual silver nanostrips placed on the top of a thin-film amorphous silicon solar cell. In the first layer, cylindrical silver nanostrips are embedded in the antireflection coating and the other one is placed just above it. Combining the two improves the absorption over the wide spectral range. A finite-difference time domain technique has been used to confirm that a vertical dual silver nanostructure improves absorption over a broad spectrum in comparison to a single layer. Size, shape, and interspacing of the nanostructures have been tuned to obtain the preeminent results. This optimized geometry gives a total quantum efficiency of 32.02% under AM1.5G.

Thickness and Annealing Effects on the Particle Size of PLD Grown Ag Nanofilms

This work reports the effects of film thickness and annealing temperature on pulsed laser deposited silver nanofilms. Structural and optical properties of nanostructures are studied with scanning electron microscopy, energy dispersive analysis of x-ray, x-ray diffraction, and UV-visible spectroscopy. A direct relation is observed between the film thickness and dimensional range of silver nanoparticles that can be produced by annealing. With the increase in annealing temperature, formation of well-separated nanoparticles is promoted. Optical characterization of different samples shows the effective coupling of silver nanoparticles, and surface plasmon resonance is observed over a wide spectrum. Finite-difference time-domain (FDTD)-simulated results illustrate shifts in the plasmon resonance wavelengths due to the combination of different nanoparticle sizes and support experimental findings. This generic study produces a wide range of plasmonic nanostructures and may be extremely useful for various applications.

Silicon nanospheres for directional scattering in thin-film solar cells

Abstract. Reducing active layer thickness of solar cell stresses on efficient light trapping mechanisms to keep the cell efficiency intact. Directional light scattering and promising refractive index of silicon nanoparticles make them encouraging scattering centers for thin-film silicon solar cells. Finite-difference time-domain simulations are used to study the optical properties of silicon nanospheres embedded in the top and bottom buffer layer of solar cells. Diameter of a silicon nanoparticle plays a crucial role in the forward and backward scattering of incident light into the cell. Silicon nanospheres outperform commonly used metallic and dielectric nanospheres and trapped the incident light over a broad spectrum. Silicon nanospheres require special attention when placed in both the buffer layers of the solar cell simultaneously, and lateral displacement of the silicon nanospheres at the top buffer layer with respect to nanospheres at the bottom buffer layer is beneficial. Lateral displacement of nanospheres provides a total quantum efficiency of 51.49% in comparison to 21.9% of the pristine cell. These exceptional scattering competencies of silicon nanospheres make them a promising candidate for photovoltaic applications. Silicon scatterers may be used with well-established fabrication techniques.

Effect of particle clustering of silver nanoparticles on ultrathin silicon solar cell

Particle clustering is a major concern for uniform dispersal of nanoparticles in various deposition procedures. Well separated uniform distribution of metal nanoparticles is essential for effective coupling of surface plasmons. This work experimentally and theoretically, discusses the effect of nanoparticle clustering on the light trapping efficiency of silver nanoparticles. Pulsed laser deposition system has been used for deposition of silver nanoparticles, and substrate heating has been used to promote uniform distribution of nanoparticles. Pre-heated substrate depositions are compared with corresponding post-annealed samples. XRD, FESEM, Photoluminescence and UV-visible spectroscopy have been used to study the variations in their structural and optical properties. Mono-dispersal of silver nanoparticles for pre-heated substrates results in sharper surface plasmon resonance in comparison to post-annealed samples. Mie theory is used to estimate the particle size of the nanoparticles and findings are in accordance with quantitative analysis of FESEM images. Finite-difference time domain technique is used to discuss the effect of particle distribution on an ultrathin film silicon solar cell. Device degradation is observed as a result of clustering of silver nanoparticles. Hence, mono-dispersal of plasmonic nanostructures is important for required results and pre-heated deposition of metal nanoparticles by pulsed laser deposition can effectively solve the problem of particle clustering.

Thermal stability of PLD grown silver nanoparticles

Present work discusses the stability of silver nanoparticles at different annealing temperatures. Air muffle furnace annealing is performed to study the thermal stability of pulsed laser deposited silver nanoparticles. Silver reacts with atmospheric oxygen to form silver oxide at annealing temperatures below 473K and thermal decomposition of silver oxide takes place at temperatures above 473K. Oxide formation results in core shrinkage of silver, which in turn affects the surface plasmon resonance of silver nanoparticles. With increase in annealing temperature, the surface plasmon effect of nanoparticles starts to fade. SEM, XRD and UV-vis spectroscopy have been performed to analysis various structural and optical properties.

Embedded vertical dual of silver nanoparticles for improved ZnO/Si heterojunction solar cells

Abstract. A ZnO/Si heterojunction solar cell is studied with plasmonic nanoparticles embedded in the active layer. Two layers of silver nanoparticles are embedded in the ZnO layer. The effect of various parameters such as vertical-interparticle distance, horizontal-interparticle distance, relative dimensions of nanoparticles, and order of particle diameters are discussed in detail. Finite-difference time-domain studies suggest that particle dimensions of the top layer of silver nanoparticles should be less than the dimensions of the underneath layer of silver nanoparticles. The resulting structure acquires the benefits of each layer and improves the device performance over a broad spectrum. The dielectric separation of plasmonic layers is observed to be an important factor in favorable plasmonic response. Electric field diagrams are used to study the scattering of an incident field by proposed structure. Results are encouraging and suggest more concerted studies of multilayer plasmonic structures.