Selenium Nanoparticle Applications

Introduction

Selenium is an essential trace element, vital for both human and livestock nutrition. It is a necessary dietary constituent of at least 25 human selenoproteins and enzymes containing selenocysteine. Due to its many health benefits selenium is a common additive to animal feeds and nutritional products. Additionally, as selenium is a semi-conductor and photoelectrically active it has more advanced applications such as xerography and solar cell assembly. Selenium rarely occurs in its elemental state and has typically been observed in its organic (selenomethionine, selenocysteine) or inorganic (selenate, selenide, selenite) forms.

The development of uniform, monodisperse, nanometre sized selenium particles has gained commercial interest as such nanoparticles often display interesting electrical, optical, magnetic, and chemical properties in comparison to their bulk counterpart materials. The application of selenium nanoparticles (SeNPs) is of particular interest as it has been shown to enhance selenium’s biological and photoelectric properties. Furthermore, SeNPs are biocompatible and non-toxic, and exhibit low cytotoxicity compared to the counterparts, selenite (SeO32-) and selenate (SeO42).

Fig. A. Photographic images of six size-distinguishable selenium colloids. From left to right, the images represent mean particle diameters of 20.0±6.1,70.9±9.1, 101.6±9.8, 146.1±23, 182.8±33.2, and 240.4±32.2 nm.

Fig. B. TEM image of uniform, monodisperse chemically synthesised selenium nanoparticles

Application Area 1: Increased bioavailability of Human Food/Animal Feed supplements

Nanosized particles may offer nutritional benefits such as enhanced absorption, bioavailability, antimicrobial activity, and excretion of the nanomaterials. The supplementation of animal nutrition products with SeNPs has shown highly promising outcomes when added to monogastric, ruminant and aquatic feeds (see Fig. 1. for applications of SeNPS in animal feeds). Nanoparticle delivery of minerals has been shown to be effective in improving feed conversion ratio, promote growth and development of muscle cells, improve the gut microbial environment, treat common parasitic disease such as coccidiosis and reduce mortality in poultry. Traditionally selenium is added to animal feeds in either its inorganic (selenite) or organic (seleno-methionine) form.

However, the use of selenium in its nanoparticle form in animal feed may be an attractive alternative as it does not need to be metabolised before being incorporated into selenoproteins and is thus more bioavailable than inorganic selenium. At present, there is a void of human SeNP supplementation trials and commercial products, however this is an area of highly promising research.

Fig. 1. Applications of SeNPs in animal feeds

Application 2: Medical device

Nanoparticles have been widely investigated for various medical applications because of their high surface-to-volume ratio’s and their smaller size when compared with conventional micron-size particles. Their high surface area provides more sites for interacting with biological entities and for functionalization with other bioactive molecules such as anticancer and antibacterial drugs. Nanostructured selenium increases the surface area available to interact with and kill bacteria in addition to changing the surface morphology to ultimately inhibit the attachment of bacteria. Additionally, SeNPs have shown a sevenfold lower acute toxicity than sodium selenite in mice showing less prooxidative effects.

Biofilms are a common cause of persistent infections on medical devices as they are easy to form and difficult to treat. SeNPs may be coated on the surface of medical devices (such as those used for catheters, orthopaedic prostheses, contact lenses, prosthetic heart valves etc.) to prevent biofilm formation. A study by Wang et al. demonstrated that polycarbonate medical devices coated with SeNPs strongly inhibited the growth of S. aureus bacteria on the surface after 24 and 72 h by 91 and 73% respectively, when compared with uncoated polycarbonate surfaces. Importantly, this was achieved without using antibiotics but rather an element natural to the human body.  Fig. 2 illustrates the decrease in S. aureus densities with increasing selenium concentration on the surface of polycarbonate.