Shazia Tanvir

Enhanced colloidal stability and antibacterial performance of silver nanoparticles/cellulose nanocrystal hybrids

The aggregation of nanoparticles has been shown to significantly reduce the activity of nanomaterials, resulting in inferior performance. As an alternative to the use of traditional capping agents, stabilization of unstable nanoparticles with water-dispersible and biocompatible carriers is a promising strategy. A bioinspired coating strategy was developed and the hybrid nanoparticles displayed excellent colloidal stability that significantly improved antibacterial activity when silver nanoparticles (AgNPs) were used as a model. Cellulose nanocrystals (CNCs) were first modified with dopamine, followed by in situ generation and anchoring of AgNPs on the surface of CNCs through the reduction of silver ions by polydopamine coated CNCs. The results indicated that the dispersion stability of AgNPs was significantly enhanced by the CNC, which in turn resulted in more than fourfold increase in antibacterial activity based on antibacterial studies using Escherichia coli and Bacillus subtilis.

Coenzyme based synthesis of silver nanocrystals.

In this work we have carried out systematic studies to identify the critical role of a coenzyme (β-NADPH) to synthesize silver nanoparticle. Interestingly, both roles of reducing and stabilizing agents are played by β-NADPH. Nanoparticles obtained by this route exhibit a good crystallinity, a narrow size distribution and excellent stability in aqueous solution. The most advantageous points of this single-step environmentally friendly approach are that it takes place at nearly room temperature (20 °C), overcomes many limitations encountered in other biological methods (such as the restricted concentration of AgNO₃, maintenance and manipulation of microorganisms, preparing extracts and contamination from residual reactants), bypasses the use of surfactants or capping agents and does not necessitate pH adjustment. The nano-Ag were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), dynamic light scattering (DLS), zeta potential, UV-vis, and energy-dispersive X-ray spectroscopy (EDX). DLS, TEM and XRD measurements showed the formation of nano-Ag with an average diameter of 20.77±0.67 nm. XRD studies confirmed the nanocrystalline nature of the silver particles. Zeta potential measurements revealed that the particles are surrounded with negatively charged groups (-41±5 mV) making them stable in an aqueous medium. The EDX spectrum of the silver nanoparticles confirmed the presence of elemental silver signal in high percentage. In addition to the easy and ecofriendly method of synthesis, β-NADPH can be regenerated by enzymatic means through glucose 6-phosphate dehydrogenase, potentially making the synthesis more cost effective.

Development of immobilization technique for liver microsomes.

In the present report, physically adsorbed rat liver microsomes were used in order to optimize the immobilization of membrane proteins on solid surfaces for use in biosensing and microreactor applications. Physical adsorption was used to form thin films on solid supports (gold, mica, macroporous aluminum oxide membrane). The characterization of the films was performed by surface plasmon resonance (SPR), atomic force microscopy (AFM) and environmental scanning electron microscopy (ESEM). Commercially available macroporous aluminium oxide membranes with a high surface area, allow the retention of a high amount of microsomal membranes in the form of a thin film. Microsomal film functionality was tested by monitoring the activities of several enzymes of phases I and II. Microsomal modified supports can be re-utilized for the same or different substrate after washing with appropriate buffer.

Activity of immobilised rat hepatic microsomal CYP2E1 using alumina membrane as a support

Porous alumina membranes are attractive materials for the construction of biosensors and also have utility for the production of immobilised enzyme bioreactors. Microsomes from rat liver were adsorbed onto alumina membrane activated by silane. Microsomal membranes were pumped through the channels where they became immobilised by binding to amine groups on the surface of the alumina membrane. In an effort to gain a quantitative understanding of the effects of microsomal film growth on enzyme activity, we compared the para-nitrophenol (pNP) hydroxylase activity of the microsomes by varying the amount of microsomes fixed in alumina microchannels. The alumina membrane was placed in a fluidic device at a fast flow that afforded short residence time (seconds) to obtain transformation of pNP to 4-nitrocatechol (pNC), which was detected by LC-MS/MS. This enabled the use of this bioreactor where CYP2E1 activity is low and tissue sources are limiting. The microsomes, successfully immobilised on the alumina membranes, were used to produce stable biocatalytic reactors that can be used repeatedly over a period of 2 months.

Poly-L-arginine Coated Silver Nanoprisms and Their Anti-Bacterial Properties

The aim of this study was to test the effect of two different morphologies of silver nanoparticles, spheres, and prisms, on their antibacterial properties when coated with poly-L-arginine (poly-Arg) to enhance the interactions with cells. Silver nanoparticle solutions were characterized by UV–visible spectroscopy, transmission electron microscopy, dynamic light scattering, zeta potential, as well as antimicrobial tests. These ultimately showed that a prismatic morphology exhibited stronger antimicrobial effects against Escherichia coli, Pseudomonas aeruginosa and Salmonella enterica. The minimum bactericidal concentration was found to be 0.65 μg/mL in the case of a prismatic AgNP-poly-Arg-PVP (silver nanoparticle-poly-L-arginine-polyvinylpyrrolidone) nanocomposite. The anticancer cell activity of the silver nanoparticles was also studied, where the maximum effect against a HeLa cell line was 80% mortality with a prismatic AgNP-poly-Arg-PVP nanocomposite at a concentration of 11 μg/mL. The antimicrobial activity of these silver nanocomposites demonstrates the potential of such coated silver nanoparticles in the area of nano-medicine.

Biosensing of reactive intermediates produced by the photocatalytic activities of titanium dioxide nanoparticles.

The development of an enzyme based biosensing method is described for evaluating the toxicity of solutions treated by titanium dioxide photocatalysis. The method is based on the potential of rat liver microsomal glutathione transferase ability (mGST) to get enhanced in the conditions of chemical and oxidative toxicity. Phenol is taken as a model pollutant due to its toxicity and prevalence in industrial processes. Chemical analysis of the parent compound, products and acute toxicity assays using the mGST activity, were conducted during and after the various photocatalytic treatments. The maximum mGST activity was observed from 60 and 120 min treated samples. This post-treatment toxicity might be due to toxic phenolic products, which may include p-benzoquinone, hydroquinone, benzenetriol and other intermediates. The enzymatic activity pattern observed after photocatalytic treatment corresponded well with the chemical degradation data obtained by HPLC-UV. The mGST assay seems to be an easy to use and promising approach for evaluating the effectiveness of wastewater treatment processes.

Colorimetric enumeration of bacterial contamination in water based on β-galactosidase gold nanoshell activity

In this study we report a method for the rapid and sensitive estimation of bacterial cell concentration in solution based on a colorimetric enzyme/gold nanoshells conjugate system. The CTAB capped gold nanoshells are electrostatically attracted by both the bacterial surface and the enzyme β-galactosidase. The preferential binding of cationic (CTAB)-functionalized gold nanoshells to the more negative bacterial surfaces leaves active β-galactosidase in solution, providing an enzyme-amplified colorimetric response of the binding event. A progressive increase in the enzyme activity is evidenced by the conversion of the yellow-orange CPRG substrate into the red chromophore chlorophenol red, which can be correlated with increasing bacterial cell numbers. Using this strategy, the quantification of bacteria at concentrations as low as 10 bacteria/mL of solution has been achieved. The present method of bacterial cell load assessment offers a distinct potential advantage over other conventional methods such as plate counting in terms of ease of operation, rapidity, high sensitivity and quantitative detection of bacterial cells.