Gold nanoparticles can be used in a variety of ways, i.e. as active ingredient carriers in medicine. Although their synthesis is already very successful today, it is difficult to predict how the particles interact with the environment and humans. Scientists are therefore intensively investigating the behaviour of nanoparticles in order to make them more efficient and safer.
In the last 30 years, a range of scientific fields have benefited from our ability to manipulate and control nanoparticles. The relatively new field of nanotechnology is featuring more in our daily lives and has massive potential for the future. It is transforming science — from creating entirely new materials, to understanding the structures behind unusual scientific properties.
Nanoparticles are defined as particles between one and 100 nanometres in size, and can either be artificially produced or found in natural systems (for example as part of biological systems such as viruses or bone matrix). They range from carbon-based nanomaterials like fullerenes, to metal-based, such as silver and gold nanoparticles, to nano-polymers.
Multiple variables can be altered to define the properties of nanoparticles, offering engineers greater flexibility when designing materials to be used in our everyday lives. Nanomaterials are already used in everything from golf clubs to racing cars, and are also found in sun creams and cosmetics. The small size of the particles means they have a very high surface area to volume ratio, and thus their properties depend strongly on their size, shape and bound molecules. Nanoparticles have exciting possibilities in pharmaceuticals, as potential drug delivery vehicles and contrast agents.
A cautious step forward
While scientists have been able to fine-tune and engineer the properties of nanoparticles by changing their size, shape, and surface chemistry, predicting and controlling exactly how the particles behave at such a minute scale is an enormous challenge. This is of particular concern when it comes to using nanoparticles within the human body, or in systems where they could impact on the surrounding environment. While nanotechnology has improved lives and enabled massive progress in many areas of society, it must be acknowledged that until we are able to fully characterise their precise behaviours at every level, we cannot identify how far engineered nanomaterials expose humans, animals, and the environment to risk.
Gold nanoparticles (AuNPs) are a metal-based material proving to be a next-generation tool in nanoengineering. Thanks to their particular range of electronic, optical, sensing, and biochemical properties, AuNPs have long-been investigated for potential biological and medical applications, such as medical imaging, disease treatment, and drug delivery processes. AuNPs can be visualised as a cluster of gold atoms at the centre, surrounded a molecular layer on the surface. This surface can be manipulated to produce particular functions for the nanoparticle as a whole, through the addition of specific ligands that may target a particular type of molecule.
By exploiting this property, gold nanoparticles can make good carriers of large and small molecules, hence the interest in employing them as drug transporters to human cells. The idea of nanoparticle-based drug formulations provides a potential opportunity to address and treat challenging diseases.
Nanotechnology has proven beneficial in the treatment of cancer, aids and many other conditions, also providing advancement in diagnostic testing. The nanoparticles can be developed into smart systems, encasing therapeutic and imaging agents, but gold in particular is thought to be suited to systems that can deliver drugs to specific tissues and provide controlled release therapy. Such systems enable researchers to resolve the main critical issues encountered with conventional pharmaceutical treatments such as the nonspecific distribution, rapid clearance, uncontrollable release of drugs, and low bioavailability. The sustained and targeted drug delivery which could be provided by AuNPs would minimise the toxicity associated with many drugs, and the lack of excess substance means that patients can rely on less frequent doses.
However, predicting exactly how far these nanoparticles are ab- sorbed by the cells, central to their toxicity, is very difficult. As such, so is understanding any potential associated risks to health through using these nanomaterials in the human body.
A collaboration of researchers examined this further. Scientists from the Institut Laue-Langevin (ILL), Tampere University, University of Helsinki, Norwegian University of Science and Technology, and Université Grenoble Alpes, investigated the physical and chemical influences when gold nanoparticles interact with a model biological membrane.
Identifying the behavioural mechanisms taking place is vital for applying gold nanoparticles in medicine. Enhancing our understanding of the factors that determine whether nanoparticles are attracted or repelled by the cell membrane, whether they are adsorbed or internalised, or whether they cause membrane destabilisation, will help us to ensure that nanoparticles interact with our cells in a controlled way. Such atomic-level intricacies could be the difference between a drug being effectively delivered to a site and carrying out the desired effect, or a drug being unintentionally absorbed into cells, causing systematic damage.
As outlined in the journal Small, the researchers used a combination of neutron scattering techniques and computational methods to study the interaction between positively charged cationic gold nanoparticles and model lipid membranes, with the aim of revealing the possible nanotoxicity.
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