Chris Binns - Introduction to Nanoscience and Nanotechnology

Figure I.5 Theranostic nanoparticle for the diagnosis and treatment of cancer.(a) Core shell–shell nanoparticles (nano‐onions) that can be produced by gas‐phase synthesis (see Chapter 5). (b) The same technology can also produce dumbbell particles of different elements (Janus particles) or the same element. (c) A dumbbell iron nanoparticle with an intermediate shell and an outer gold shell with an attached protein that will find and attach to cancer cells. When in situ, the particle can perform a range of therapeutic and diagnostic actions (“theranostics”) as described in the text. The electron microscope images in (a) and (b) were reproduced with permission from [6, 7] respectively.

Source : Reproduced with permission from Llamosa et al. [6], Reproduced with permission from Krishnan et al. [7].

Combining the abilities of the synthesis method, Figure I.5c shows a dumbbell nanoparticle with an iron core coated with an intermediate shell of another metal and finally with a gold shell. In addition, a protein has been attached that is a piece of antibody, known as a nanobody (see Chapter 8, Section 8.1.7), which is able to locate and attach to specific cells in the body, in particular, cancer cells. Once attached to a cancer cell, the nanoparticles can perform a range of therapeutic and diagnostic functions (this combination of therapy and diagnosis is often referred to as “theranostics”). The magnetic core can be heated by applying an oscillating magnetic field from outside the body to which tissue is transparent, thus, heat is generated only at the cellular level of the cancer. Gentle heating to just a few degrees above core body temperature causes the cell to shut down and die in an orderly process known as apoptosis.

This method, referred to magnetic nanoparticle hyperthermia and described in Chapter 8, Section 8.2 is potentially a symptom‐free and generic treatment for cancer and is waiting for designed nanoparticles such as those shown in Figure I.5c. Hyperthermia can also be induced by near infra‐red light, to which tissue is relatively transparent, interacting with the gold shell. The magnetic core can be used to provide high‐resolution images of the tumor by magnetic resonance imaging (MRI) or a new method known as magnetic particle imaging (MPI). As well as heating, the gold shell acts as a powerful X‐ray absorber to provide images of the tumor using computerized tomography (CT). The dumbbell shape of the nanoparticle also makes it possible to remotely measure the temperature at the site so that the hyperthermia can be accurately controlled. Finally, the intermediate shell can be used to introduce additional functionality, for example, it could be a radionuclide for alternative imaging methods. Thus, this type of nanoparticle can act as a nanoscale treatment centre that can provide a range of therapies and diagnoses with the most appropriate set chosen for the type of cancer. This is a highly sophisticated example of evolutionary nanotechnology.

Finally, the most far‐reaching version of nanotechnology, described as Radical Nanotechnology by Richard Jones, is the construction of machines whose mechanical components are the size of molecules. The field has bifurcated into two distinct branches, that of molecular manufacturing in which macroscopic structures and devices are built by assembling their constituent atoms, and nanorobots or nanobots, which are invisibly small mobile machines. Molecular manufacturing was originally proposed by the Nobel laureate, Richard Feynman in his famous lecture in 1959, and was subsequently advocated with much enthusiasm by Eric Drexler [8]. In 1990, the IBM research laboratories in Zurich demonstrated that they could move and position individual atoms using a scanning tunneling microscope (STM – see Chapter 5, Section 5.4.2) lending support to the idea that molecular manufacturing may, at least in principle, be possible. The problems and the emergence of some enabling technologies for molecular manufacturing are presented in Chapter 9.

Nanobots have generated a good deal of controversy, especially ones that can play atomic lego and build anything out of atoms lying around. If this was possible, then one could, in principle, build a nanobot that moved around exploring the surface it occupied. If it was equipped with an assembler that could assemble atoms and molecules, it could make a copy of itself by rooting around and finding the atoms it needed to reproduce. Since each nanobot could make multiple copies of itself, the population could increase exponentially and would quickly produce a sufficiently vast army to build macroscopic objects. Drexler himself pointed out the doomsday scenario where the nanobots multiply out of control like a virus and eventually exist in such vast numbers that they could rearrange the atoms of the planet to produce a kind of “grey goo.” Unfortunately, this scenario has tended to hijack discussions on radical nanotechnology, and since the two branches of radical nanotechnology have been melded together in the public debate there is a general feeling that all radical nanotechnology is dangerous. The reality is that exponentially self‐replicating machines are not required for molecular manufacturing [9], and nanobots do not need to be built with assemblers to self‐replicate in order to perform useful functions, as shown in Chapter 9, Section 9.3 for the case of medical nanobots.

There is a scientific debate about whether this technology is feasible, even in the long term, or indeed desirable, but the discussion has moved on from generalities to a consideration of the detailed processes required for molecular manufacturing (see Chapter 9and the references therein). A frequently proposed argument in favor of radical nanotechnology is that it already exists in all living things. Biological cells are filled with what may be regarded as nano‐machines and molecular assemblers. Biology, however, is very different to the nanoscale process‐engineering path envisaged by radical nanotechnologists, as explained in Soft Machines [2]. It is fair to say that both the feasibility and timescale of radical nanotechnology divides the community. The point is that, while incremental nanotechnology exists and evolutionary nanotechnology is just coming into the frame, radical nanotechnology, if feasible, is probably decades away. Whatever the twists and turns of the debate, once we get away from the argument over nanobots, there is no doubt that the ability to produce nano‐machines and achieve safe non‐exponential molecular manufacturing will reap enormous benefits.

It is possible that the solution to some of the more difficult technological problems involved with radical nanotechnology may arise from a better fundamental understanding of the true nature of empty space. Quantum theory predicts new types of force at very short distance scales (nanometers) arising directly out of the quantum properties of vacuum. Although we can only detect these forces with very sensitive instruments (the tools of nanotechnology in fact – see Chapter 10), to a nanoscale machine whose components are within nanometers of each other, these forces will be as natural as a part of their environment as gravity is to us. Research on these forces and how to utilise them in nanotechnology is already being undertaken by several research groups worldwide. This may be one of the missing links between biology and radical nanotechnology, that is, natural systems, whose inner workings happen on the same scale as nanomachines have evolved over billions of years and must have utilised all available forces including the exotic ones.