Environmental Science: Nano Blog

Engineered water nanostructures (EWNS), the latest weapons for tackling airborne pathogens, start off as nothing more than atmospheric water vapour.

Despite advances in antibiotics, vaccines and infection control, infectious diseases continue to affect hundreds of millions of people each year and the number of antibiotic resistant bacteria is on the rise. Therefore, there is an urgent need for innovative, effective and low-cost technologies in the battle against airborne infections. Upper-room UV irradiation, air filtration, photocatalysis and biocidal gases are the current methods most commonly used for air disinfection. However, these methods come with a variety of drawbacks such as potential health risks and high costs.

Philip Demokritou and colleagues from the Harvard School of Public Health and the National Institute of Occupational Safety and Health in the US, have designed a system that transforms atmospheric water vapour into EWNS. With a size of only 25nm, the nanostructures are highly mobile and remain in room air for a long time due to their high electric charge. Disinfection of the air is achieved as the nanostructures contain reactive oxygen species, such as hydroxyl and superoxide radicals, which interact with the outer membranes of bacteria, rendering them inactive.

Toxicological studies on mice by Demokritou’s team have shown that the EWNS have minimal toxicological effects. No respiratory tract toxicity was found at exposure levels and times higher and longer than those needed to inactivate the bacteria. Demokritou explains that the radicals are harmless to cell membranes in the lungs of test animals because ‘the organic matter in the lung lining fluid which covers the epithelial cells neutralises the reactive oxygen species, so they never reach the cells.’

‘The proposed method has the potential to transform the way we currently control infectious diseases,’ says Demokritou, ‘if proven effective in practice, it could be used to create “shields” to protect people in their microenvironments.’

Vishal Shah, an expert in microbiology from Dowling College in New York, US, agrees that the research presents ‘a proof-of-concept for an interesting technology that could help improve air quality, particularly in high moisture indoor environments.’ Shah adds that in the future, he would ‘look forward to seeing results describing the efficiency of the technology to inactivate other viruses and gram positive bacteria like streptococci and staphylococcus.’

The team now intend to extend their research to ascertain if EWNS can disinfect fresh produce.

Download the paper for free here, or visit the original Chemistry World post!

A phospholipid component of plants can potentially provide versatile, environmentally benign ligands in the synthesis of asymmetric gold nanoparticles (GNPs). This paper by Benjamin Ayres (Portland State University) and Scott Reed (University of Colorado Denver), demonstrates how this can provide benefits in terms of both possible application and environmental performance of these materials.

Asymmetric GNPs have been utilised for a wide range of applications including biomedical sensors and components of electronic and photonic devices. In order to move towards a large scale production of asymmetric GNPs, a synthetic method is required that is economical and reproducible, as well as displaying suitable green credentials.

The shape and size of GNPs are crucial to governing their electronic and optical properties. There is a need therefore to gain a good understanding of the synthetic process at a molecular level, in order to optimise the process from the perspective of both desired application and environmental impact, creating a method that can be easily controlled and reproduced.

Conventional synthetic methods traditionally involve seed-mediated synthesis using alkyl ammonium salts (e.g. CTAB) as ligands. These methods are unsustainable and non-biocompatible due to the toxic nature of the compounds used, and often require excess ligand and post-synthetic processing e.g. using ligand exchange in order to be used for in vivo applications.

The method described by Ayres and Reed involves reduction of bromoauric acid by ascorbic acid in the presence of ligands derived using biogenic phospholipid extracts from crude soybean lecithin. This provides a cheap, readily available and renewable feedstock for the process, avoiding use of fossil-fuel derived materials.

A key parameter of generated GNPs is their localized surface plasmon resonance (LSPR). In order for GNPs to be suitable for medical applications (e.g. biosensors, in-vivo imaging and phototherapeutic treatments) the LSPR needs to be in the near infrared (NIR) region.

It was shown, using UV-Vis spectroscopy and high resolution transmission electron microscopy (TEM) that the described method produces a mixture of spherical and triangular prismatic GNPs that exhibited an LSPR in the NIR region as well as extended stability with no aggregation.

Furthermore, the method includes chemical identification of the specific molecular component of soy lecithin that is the source of asymmetric growth. Soy lecithin is composed predominantly (~75%) of phosphatidylchorine (PC). However, separation of different GNP shapes using preparatory gel electrophoresis, and analysis of lipid extracts by LC-MS indicated phosphatidic acid (PA) was crucial to GNP asymmetric growth.

Indeed, it was shown that GNPs produced from lower purity PC (30%) showed NIR LPSR and were stable, while higher purity PC (95%) produced only spherical GNPs which aggregated over time and displayed LSPR only in the UV-Vis spectrum. When spiked with PA, the growth solutions of PC₉₅ displayed a second LSPR in the NIR, which shifted further red as more PA was added.

This study presents a biocompatible method for GNP production using environmentally benign ligands. It also demonstrates how gaining molecular level understanding of the synthetic process allows control over the GNP shape and size, based on lipid composition and/or specific plant material used. This therefore provides benefits both from the perspective of the desired application and the environmental impacts.

Environmental Science: Nano is providing free access upon registration* to all content published during 2014 and 2015. To get your free download of this paper, please follow the link below:

A minor lipid component of soy lecithin causes growth of triangular prismatic gold nanoparticles, Benjamin. R. Ayres and Scott. M. Reed, DOI: 10.1039/C3EN00015J

*Free access to individuals is provided through an RSC Publishing personal account. It’s quick, simple and more importantly free to register!

As nanotechnology continues to develop at a fast growing speed, more research efforts should focus on the assessment of nanotoxicity in order to better understand whether engineered nanoparticles (ENPs) pose hazards upon exposure. ENPs have been used in a large variety of products (from toothpaste, soap, sunscreen lotion to plastic ware, electronics, cement, paint, etc.) and therefore the likelihood for ecological exposure to these nanoproducts in relation to their leachable by-products is inevitable.

Dubey and co-workers highlight the importance of assessing the interaction of ENPs with naturally occurring colloids in relation to environmental factors. Upon entering the aquatic system, these factors could modify their colloidal stability and ultimately affect their toxicity. Their studies focused on silver nanoparticles (AgNP) which have been widely used for their broad spectrum of antimicrobial and plasmonic properties. In particular, Dubey et al investigated the potential effects of multiple water chemistry on the colloidal stability, dissolution rate and antibacterial activity of citrate-coated silver nanoparticles (Citrate-AgNPs) against Escherichia coli. Concomitantly, toxicity studies of Citrate–AgNPs and AgNO₃ were also performed in the river water samples collected across three seasons.

The work carried out by Dubey and co-workes underlines the importance of evaluating aquatic toxicity of ENPs in order to understand the potential implications on the ecosystem’s health and functions.

Read the full article for free!

Natural Water Chemistry (Dissolved Organic Carbon, pH, and Hardness) Modulates Colloidal Stability, Dissolution, and Antimicrobial Activity of Citrate Functionalized Silver Nanoparticles
Lok R. Pokhrel, Brajesh Dubey and Phillip R. Scheuerman
Environ. Sci.: Nano, 2014, Advance Article
DOI: 10.1039/C3EN00017F

Fancy submitting an article to Environ. Sci.: Nano? Then why not submit to us today or alternatively email us your suggestions.