The Atomic Force Microscope (AFM) is a key tool for nanotechnology. This instrument has become the most widely used tool for imaging, measuring and manipulating matter at the nanoscale and in turn has inspired a variety of other scanning probe techniques. Originally the AFM was used to image the topography of surfaces, but by modifying the tip it is possible to measure other quantities (for example, electric and magnetic properties, chemical potentials, friction and so on), and also to perform various types of spectroscopy and analysis. Increasingly, the AFM is also becoming a tool for nanofabrication. Relatively new is the use of AFM in cell biology. Researchers in Switzerland have now demonstrated novel cell biology applications using hollow force-controlled AFM cantilevers - a new device they have called FluidFM.
A major concern in microbiology is to determine whether a bacterium is dead or alive. This crucial question has major consequences in food industry, water supply or health care. While culture-based tests can determine whether bacteria can proliferate and form colonies, these tests are time-consuming and work poorly with certain slow-growing or non-culturable bacteria. They are not suitable for applications where real-time results are needed, e.g. in industrial manufacturing or food processing. A team of scientists in France has now discovered that living and dead cells can be discriminated with a nanotechnology technique on the basis of their cell wall nanomechanical properties.
For the past 20+ years, the atomic force microscope has been one of the most important tools to visualize nanoscale objects where conventional optics cannot resolve them due to the wave nature of light. One limiting factor of conventional AFM operation is the speed at which images can be acquired. Over the past five years, researchers have been developing a high-speed AFM capable of video-rate image capture. An AFM with this ability enables nanoscale processes to be observed in real-time, rather than capturing only snap-shots in time. An obvious application of this instrument is to modify the sample surface while observing changes in the surface topography. Successful demonstration of this would indicate the potential for a new generation of fabrication tools. Scientists have now done exactly that.
Over the past 25 years, Scanning Tunneling Microscopy (STM) has brought us extremely detailed images of matter at the molecular and atomic level. STM, which is a non-optical technique, works by scanning an electrical probe over a surface to be imaged to detect a weak electric current flowing between the tip and the surface. The STM allows scientists to visualize regions of high electron density and hence infer the position of individual atoms and molecules on the surface of a lattice.
Researchers also believe that the strength of time-lapsed high-resolution STM work to unravel complex surface reactions would allow them to achieve one of the 'Holy Grails' within the area of surface science, which is to directly observe chemical reactions at the atomic scale. A research team in Denmark has now shown that, by means of high-resolution STM studies in conjunction with density functional theory calculations, it is possible to follow the intermediate steps of a complex oxidation reaction.
Crystalline nanoporous compounds have attracted the attention of scientists and materials engineers because of the interest in creating nanoscale spaces and the novel phenomena in them. Nanoporous materials find applications in many chemical processes such as separation and catalysis and are also heavily researched as storage materials, for instance in hydrogen fuel cells. Researchers still lack a complete understanding of the mechanism that leads to, and occurs during, crystal growth. Only once scientists achieve full control of properties such as composition, structure, size, morphology, and the presence and form of defects within the crystals can they fully exploit the benefits of crystalline nanoporous materials for the fabrication of novel materials. Researchers in the UK have now presented definitive real-time evidence of the crystal growth mechanism in what appears to be the first high-resolution observation of in-situ crystal growth of a crystalline nanoporous material monitored using atomic force microscopy (AFM).
The processes by which molecules pass through pores in thin films and biological membranes are essential for understanding various physical, chemical and biological phenomena. For instance, the fundamental behavior of molecules in porous solids and their transfer through cell membranes necessarily involves a process of molecules passing through pores - knowledge that, for instance, is crucial for the development of nanotechnology-based hydrogen storage materials for fuel tanks. So far, research methods have been based on studying the statistical average of the behavior of groups of molecules; there were no experimental approaches that examined the interaction of a single molecule with a pore. There has been a lack of experimental methods that can obtain information on the structure and orientation of the molecules as they pass through a pore, and their interactions with the pore during passage. Researchers in Japan have now succeeded for the first time in observing a long chain of a fullerene-labeled hydrocarbon passing through a nanometer-size pore in the wall of a carbon nanotube as if it were alive.
Laser-based analytical techniques such as Raman spectroscopy, fluorescence spectroscopy or the state-of-the-art laser-induced breakdown spectroscopy (LIBS) are highly sophisticated techniques to analyze minute amounts of matter with regard to its structure, elemental composition, and other chemical properties. LIBS has been shown to be capable of analyzing extremely small samples with high sensitivity - nanoliter volumes with levels of detection in water of part per million. LIBS works by focusing short laser pulses onto the surface of a sample to create a hot plasma with temperatures of 10,000 - 20,000 C. The plasma emits radiation that allows the observation of the characteristic atomic emission lines of the elements. On the downside, LIBS is complicated by the need for multiple laser pulses to generate a sufficiently hot plasma and the need for focusing and switching a powerful laser, requiring relatively large and expensive instruments.
New research coming out of Drexel University has now shown that light emitted from a new form of cold plasma in liquid permits Optical Emission Spectroscopy (OES) analysis of the elemental composition of solutions within nanoseconds from femtoliter volumes.
Detecting the presence of a given substance at the molecular level, down to a single molecule, remains a considerable challenge for many nanotechnology sensor applications that range from nanobiotechnology research to environmental monitoring and antiterror or military applications. Currently, chemical functionalization techniques are used to specify what a nanoscale detector will sense. For biological molecules, this might mean developing an antibody/antigen pair, or an alternative synthetically generated ligand. For chemical gases, it is much more challenging to develop the right 'glue' that sticks a given gas to a substrate. The advantage of spectroscopic techniques such as Raman, infrared, and nuclear magnetic resonance spectroscopy is that they are label-free, i.e. they require no preconditioning in order to identify a given analyte. They are also highly selective, capable of distinguishing species that are chemically or functionally very similar. On the downside, spectroscopic methods face enormous challenges in measuring dilute concentrations of an analyte and generally involve the use of large, expensive equipment. This article describes a novel chemical detection technique called nanomechanical resonance spectroscopy.