Writing with Lightning (Resubmission)

Lead Research Organisation: University of Sheffield
Department Name: Chemistry

Abstract

We have become accustomed to rapid advancements in computing power, and these have resulted from relentless advances in manufacturing technology that have enabled year-on-year reductions in the sizes of electronic components in integrated circuits to continue unabated for forty years. However, such advances in miniaturisation are potentially not restricted simply to computers, but may reach into many areas of life, including medicine. For example, the determination of the human genome, the complete set of genetic words from which the description of a human being is written, has recently been completed. While this is a great achievement, we do not understand the language that these words speak / how do they instruct cells to behave the way they do, to produce proteins with particular structures and functions? How are they related to disease and ageing? New technologies based on miniaturised devices have a critical role to plan in advancing our understanding. Such devices can provide rapid methods for the interrogation of huge sets of data. One of our goals is to develop a zepto-array , a system based on an array of nanoscale spots of biological molecules that could be used to analyse biological specimens with a sensitivity of better than 600 molecules, a million times better than any existing technology.The extension of miniaturisation into such areas, loosely described as molecular nanoscience, raises new and demanding challenges. The patterning techniques that have been developed so effectively for electronic device manufacture are harder to apply to molecular materials. A major challenge in all such miniaturisation techniques is the lack of techniques that enable the control of molecular structure from the level of a single molecule up to about the current limit of commercial device fabrication methods, 100 nm. In this critical length scale there is no technique capable of routinely manipulating molecular structure with a resolution comparable to that of a single macromolecule. The objective of this project is to develop just such a technique.We will achieve this ambitious objective by exploiting, in combination, several recent advances and integrating them with new and sophisticated chemistries. When light is forced to go through very small holes, it diffracts, no longer forming a well-defined illumination. However, by working in the near-field , with the hole very close to a solid surface, this problem can be avoided. Recently we showed that we could write very small structures by using near-field light sources and a suitable photosensitive material. These structures were nearly as small as a single protein molecule. It has recently been found that very small spots may be illuminated by using a metal tip held very close to a surface and shining light on it. The illuminated area may be even smaller than when an aperture is used. However, this has not been explored as a tool for patterning molecules. We will test this here. Light is made up of photons, tiny particles. Some optical processes require the absorption of two photons at once, and these have a very sharp dependence on the light intensity. By combining these processes with the use of a metal tip to cause the illumination of the sample, we believe that we can confine the patterning process even further still. If we are successful, we will have developed a new method for doing chemistry with both exquisite chemical selectivity and unparalleled spatial resolution.
 
Description Miniaturisation has been a characteristic feature of technological advance over the past few decades. The spectacular advances in computing power that we have seen have been the result of the ingenious development of manufacturing processes to enable the construction of ever smaller components in semiconductor chips. However, the potential benefits of miniaturisation go far beyond electronic devices. There are huge possibilities for the use of miniaturised devices in medicine, for example. The most significant challenge in this area is the development of methods for the manipulation of molecular structure on small length scales through the integration of so-called top-down lithographic techniques (where patterned features are physically formed in a surface) and so-called bottom-up methods in which molecules are joined together in a spatially directed way.

It has recently been found that very small spots may be illuminated by using a metal tip held very close to a surface and shining light on it. The illuminated area may be even smaller than when an aperture is used. However, this has not been explored as a tool for patterning molecules previously. We have tested this possibility in several different ways. First, by holding a metal tip close to a surface, we have excited a second harmonic from the tip (a process in which the wavelength is effectively doubled). This has enabled us to form nanostructures in a thin film of organic molecules. For example, lines have been written in a protein-resistant oligo(ethylene glycol) terminated film. Second, we have used titania-coated probes, held close to a surface, to modify organic films through a photo-catalytic effect (rather like the one that forms the basis for self-cleaning windows, but used instead to initiate a chemical reaction). This has proved very effective and has enabled us to write protein structures only a few molecules wide. Patterns have been formed simply, and easily, on a variety of substrates.

Third, we have looked at the possibility of using so-called two-photon processes. Light is made up of photons, tiny particles. Some optical processes require the absorption of two photons at once, and these have a very sharp dependence on the light intensity. We have developed several different approaches to using two-photon processes. We have synthesised molecules specifically designed to absorb two photons. These have silane head groups, for adsorption onto oxide surfaces, and are based on nitrophenyl protecting groups coupled to extended conjugated systems, inspired by our recent considerable success with single photon nitrophenyl protecting group chemistries, which are synthetically versatile and highly efficient. We have developed of a series of molecules (aryl azides and diaziridines, with both thiol and phosphonic acid head groups for attachment to gold and oxide surfaces) that absorb very strongly in the near-UV region. They absorb weakly in the IR at 720 nm but absorption of two 720 nm photons is equivalent to absorption of a single 360 nm photon. The azide binds primary amines readily, and we have found that exposure of the azide surface provides a convenient and very general surface conjugation strategy. Exposure has been demonstrated under liquid reagents, opening up the possibility of sequential processing operations in a flow cell, which may be useful, ultimately, for commercialisation. These methodologies have been used in a variety of ways, including, for example, the fabrication of protein nanostructures. The strategies we have developed are very promising as a means to integrate top-down and bottom-up approaches.

Several papers are in the process of preparation. Unfortunately, because of complex staffing problems, significant elements of the work could not be brought to a satisfactory conclusion until very late in the project, which has delayed the submission of papers. However, three papers are currently in draft form and further papers have yet to be written.
Exploitation Route The techniques are being taken forward by researchers on an EPSRC Programme Grant on discovering biologically inspired mecha nisms for solar energy harvesting.
Sectors Electronics,Energy,Environment,Healthcare,Pharmaceuticals and Medical Biotechnology
 
Description It is early to assess impact. As noted elsewhere, the work has also provided valuable enabling methodologies for an EPSRC Programme Grant focussed on the development of biologically inspired mechanisms of solar energy harvesting.
First Year Of Impact 2013
Sector Energy,Healthcare
Impact Types Economic