A mechanism to obtain metal “nanoscrews”unveiled at CIC biomaGUNE is published in Science Led by the Ikerbasque professor Luis Liz-Marzán, researchers at the Centre for Cooperative Research in Biomaterials CIC biomaGUNE have developed a mechanism by which gold atoms are deposited by means of chemical reduction onto previously formed gold nanorods to produce a quasi-helicoidal structure (the particles acquire chirality). This geometry enables these “nanoscrews” to interact with circularly polarized light much more efficiently than what is achieved with any other known object. Fundamental Research © Adrián Pedrazo Tardajos, University of Antwerp The research group led by Luis Liz-Marzán, which works in the field known as nanoplasmonics, uses nanoparticles of noble metals, such as gold or silver, “because light interacts in a special way with particles of this type and size", explained Liz-Marzán, Scientific Director of CIC biomaGUNE. “In this case, we studied the interaction between these chiral gold nanoparticles and circularly polarized light”. The properties of these “nanoscrews” could lead to the detecting of biomolecules in a very selective and very sensitive way. What we have here is a versatile, reproducible mechanism that is scalable for the fabrication of nanoparticles with strong chiral optical activity. Light is not normally polarized, in other words, the waves expand in practically any orientation within the beam of light. “When it is polarized, the wave only goes in one direction; when it is circularly polarized the wave rotates, either clockwise or anti-clockwise,” added the researcher. "Chiral substances tend to absorb light with a specific circular polarization, rather than light polarized in the opposite direction.” Chirality is a phenomenon that occurs on all scales: a chiral object cannot have its mirror image superimposed on it; for example, one hand is the mirror image of the other, they are identical, but if one is superimposed on the other, the position of the fingers does not coincide. The same thing occurs "in some biomolecules; and the fact that a molecule cannot be superimposed on its mirror image gives rise to many biological processes. For example, some diseases arise due to the loss of recognition of one of the two forms of the chiral substance that is responsible for a specific action,” said Liz-Marzán. As the Ikerbasque professor explained, “we have looked for a mechanism to guide the deposition of gold atoms onto nanoparticles fabricated in advance in the form of a rod so that these atoms are deposited according to a practically helicoidal structure, a kind of ‘nanoscrew’. That way the particle itself acquires a chiral geometry. This new strategy is based on a supramolecular chemical mechanism, in other words, on structures obtained through molecules associating with each other without forming chemical bonds”. Liz-Marzán asserts that “this really means being able to control the structure of the material on a nanometric scale, but inside one and the same nanoparticle; in other words, it involves three-dimensional fabrication on top of a nanometric object. In actual fact, it is almost like deciding where they have to be positioned atom by atom to obtain a structure that is truly complicated”. As a result, they can practically obtain the greatest efficiencies ever achieved in spectrometric detection with circularly polarized light. Liz-Marzán confirmed that the process can be generalised to other types of materials: “We have seen that when the same strategy is applied, platinum atoms can be deposited onto gold nanorods with the same helicoidal structure. A whole host of possibilities is thus opened up both in applications of their optical properties and in others in the field of catalysis (platinum is a very efficient catalyst). At the same time, it could lead to a huge improvement in the synthesis of chiral molecules that would be of biological and therapeutic importance.” This mechanism could also be applied to new biomedical imaging techniques, for the manufacture of sensors, etc. “We believe that this work is going to open up many paths for other researchers precisely because of the generalization of the mechanism that can be used with many different molecules. A lot of work lies ahead,” he said. The research was conducted and coordinated by CIC biomaGUNE, but they had the collaboration of research groups from other organisations: Complutense University of Madrid, the University of Vigo and the University of Extremadura, and the University of Antwerp. DOI: 10.1126/science.aba0980 Keywords nanoplasmonics, circularly polarized light, chirality, nanoparticles, nanoscrews, detection of biomolecules
