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"I speak not of space that is out of the form, around the volume, in which forms lives, but I speak of the space created by forms, that live in them, and that it is more active the more hidden it acts". (Eduardo Chillida)
The synthetic route reported in this work produces structures with (A) spherical, (B) cubic and (C) cylindrical topologies. The figure illustrates TEM images accompanied by a drawing that recreates more clearly the morphology of each nanostructure. Bimetallic single-walled hollow nanoparticles, bi- and trimetallic multiwalled hollow nanoparticles, trimetallic multichamber nanoparticles, bimetallic nanocages, nanoframes, porous and segmented nanotubes, and double-walled nanotubes are shown.
What do they have in common a maze, Russian dolls and the ship inside a bottle? The three are objects with internal structure and the three have fascinated humans since the world began. Internal structure determines the properties of objects, just think of us! And thus a perimeter becomes a dead-end, a doll into a family and the bottle into a sea or ocean. All these objects are formed differently. The gardeners sow the walls of the maze, the concentric dolls are modeled separately and assembled later, the ship enters the bottle and with a little string stretches and raises its sails. What never happens is that the sculptor or a gardener to enter the initial structure, like a giant block of marble or a dense forest, which is then modeled by carving the final shape from the inside.
This is not observed at the macroscopic scale, occurs spontaneously at the nanoscale if the ingredients are mixed properly. At the nanoworld, where the dimensions are a billion times smaller, phenomena occurring seem pure miracles at our scale. However, nanotechnology allows us on a solid and compact structure, via chemical processes designed to attack, penetrate and advance digging the initial structure and creating geometric interconnected multi-cavity hollow structures ranging from molecular labyrinths to gold fullerenes, controlled by reaction fronts at the atomic level.
These new highly complex inorganic capsules meet all the structural properties of the wrapper, as blankets, envelopes or bags. The capsules protect and carry, in this case, molecules. If additionally capsules are nanoscaled and inorganic, thanks to its high density of electronic states, they respond to light in a resonant and therefore may be open or closed, heated, manipulated by electromagnetic fields such as a cocktail of drugs transported safely to the therapeutic target and drugs administered sequentially on top of pharmacology where the dose is controlled at the cellular level. Last but not least, the synthesis of these structures is performed by controlling processes considered previously undesirable: corrosion! It's funny how the recovery of old problems, applied to the nanoscale, results in new exquisite nanostructures.
A vital aspect for the realization of this work has been the ability to observe at the atomic scale the impact of changes made in the synthesis. To do this, we had to use advanced electron microscopes allowing to analyze and visualize such beautiful shapes atom by atom and allowed us to understand the complex phenomena involved in the synthesis of these new materials.
The physical properties of materials change as the size of these is reduced. At the nanoscale, matter behaves very differently than it does in our scale of perception, and their properties are very interesting and promising for a wide variety of applications. This is one of the aspects that have fostered the development of nanotechnology.
If being able to look, touch and manipulate matter at the nanoscale is already amazing, more amazing is that we are able to work inside the nanoparticle. The surface and interior of the nanostructures can be programmed in composition and architecture to make them tiny new research laboratory chemical phenomena, optical, electrical, magnetic, thermal and mechanical stresses that occur in conditions such as those presented in such nanostructures. For example, it is possible to study quantum confinement phenomena or effect of coupling of internal and external walls electronic excitations in the presence of electromagnetic radiation, or the study of catalytic reactions within the particles. The hole left in the particle may also have different shapes and also means increased exposure to material surface reaction. It escalated into the interior, a step towards a new dimension. The gaps within the nanoparticle become excellent nanoreactors for the transportation of chemicals.
This breakthrough opens a new route for medical applications in the field of controlled drug delivery, sensor fabrication, agriculture, food, fuel cells and solar energy and photonics.
This is the work developed over the years by Dr. Edgar Gonzalez Emir and Prof. Victor Puntes in the Catalan Institute of Nanotechnology (ICN), in collaboration with Prof. Jordi Arbiol in the Materials Science Institute of Barcelona (ICMAB-CSIC).