In the last few decades, all sorts of unimaginable milestones and developments have been achieved, including those in the in the fields that study, develop, and enhance materials. One of these advancements has been the emergence and development of nanomaterials: things within the range of at least one dimension on the nanometre scale or, in other words, those which measurement equals to one billionth of a meter. In perspective, the scale difference between a nanomaterial and a cell is equivalent to that between a cell and a tennis ball.
Nanomaterials of all sorts of compositions, origins, shapes, and sizes have been developed; all share this nanometric dimension. This scale difference offers surprising characteristics and properties compared to materials of the same composition albeit normal size. This result is due to changes in interaction with other materials, light, or electricity, which subsequently gives rise to new properties while enhancing others. Notable examples include graphene, for which Andre Geim and Konstantin Novoselov were awarded the Nobel Prize in Physics in 2010, or quantum dots, small particles with high fluorescence.
The origin of these improvements is mainly attributed to two reasons: the increase in surface area and quantum effects. The surface area increases exponentially as the size shrinks, exposing more atoms to the outside and allowing for a higher interaction with other substances. To understand what is happening, you may want to imagine what occurs when you break a dice or a stone: while breaking apart, its size is reduced but the surface area increases. If we could reach nanometric dimensions, something the size of a simple dice would have the same surface area as a football field. On the other hand, quantum effects are somewhat more complex to understand, but they explain the interaction of nanomaterials with electricity, magnetic fields, or light. Nevertheless, it is important to understand that, in regular materials, we observe behaviours derived from the average quantum properties of millions of atoms. In other words, the impact is not so significant in the end. When studying or working with nanomaterials, however, we have very few atoms, and the influence of different quantum states on the final properties becomes more pronounced. These quantum effects cause nanomaterials to either change colour compared to the original material or cause insulating materials to become conductors.
Considering the aforementioned, it is clear that we are experiencing a true revolution with numerous progress and applications, but there are still significant challenges to be tackled. To achieve greater implementation, different economic and environmental requirements must be reached. The main current issues that act as limiting factors include the production complexity, the lack of stability, the cost of both production and characterization of the final materials, and the environmental and toxicity risks associated with this process. Science will always seek a solution against the odds, and this is where an emerging technique comes into play: the search in nature for tools to prepare and process nanomaterials, which would be cheaper, safer, and more efficient. This technique is known as bionanofabrication or natural microfactories for nanothings. Bionanofabrication offers various advantages over other methods such as the production of biocompatible nanomaterials, the use of environmentally friendly reagents, and milder and safer working conditions. Different organisms such as algae, fungi, silkworms, or bacteria would be responsible for shaping and processing these nanomaterials.
An example of this approach is the preparation of metallic nanoparticles, which are spontaneously produced when metallic ions come into contact with certain bacteria, fungi, and plants. These organisms control their transformation through biochemical processes as a protective mechanism, a biological system that provides precise control over the size and shape of the particles. In that way, by changing the organism, concentration, or temperature, different results can be achieved. Currently, prepared nanoparticles are being tested in areas such as disease treatment or electronics.
Another fascinating example, albeit somewhat different from the previous one, is the synthesis of nano-magnets through magnetotactic bacteria. It is not achieved through forced exposure to a metallic salt; instead, it capitalises on a type of bacteria that generates iron magnetic nanoparticles through its metabolism to orient itself. The synthesis occurs within the bacteria, transforming iron ions into magnetite particles. Once produced, these nano-magnets can be extracted and utilised, for instance, in cancer treatments based on magnetic hyperthermia.
Bacterial nanocellulose is another example of how nature has much to offer to nanoscience. Similar to plants, some bacteria can produce cellulose from sugars like glucose or fructose. However, this cellulose has nanometric fibres that are much narrower than those found in plants, with higher purity and produced without the presence of other biopolymers. The improvements bacterial nanocellulose offers have led to its use in burn dressings due to its high-water retention capacity and even as catalyst support due to its large surface area.
Bionanofabrication also includes using nanomaterials to reinforce and enhance biopolymers prepared by living organisms, such as bacterial nanocellulose or silk. The idea is simple: provide nanomaterials as a source food to silkworms and they will incorporate them into the silk they produce. Depending on what they are given, the obtained silk can be stronger, conductive, or even fluorescent.
All in all, these natural microfactories have the potential to expand the use of nanomaterials, offering greater control over their dimensions while reducing the cost and risks associated with their production. Bionanofabrication enables us to harness the tools of nature to create advanced materials. If you want to learn more about this process, I invite you to read the mini-review we published in the journal Angewandte Chemie last year [1]. Enjoy!
By Víctor Calvo Peña. Predoctoral researcher at the Instituto de Carboquímica (ICB-CSIC).
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