Borrowing from nature's micro- and nanoscale propulsion systems, nanotechnology researchers have successfully used motor proteins to transport nanosized cargo in molecular sorting and nano-assembly devices. In so-called gliding assays, surface-attached motors propel cytoskeletal filaments, which in turn transport a cargo. However, cargo and motors both attach to the filament lattice and will affect each other. While an effect of cargo loading on transport speed has been described before, it has never been explained very well. To study this effect, scientists in Germany have observed single kinesin-1 molecules on streptavidin coated microtubules. They found that individual kinesin-1 motors frequently stopped upon encounters with attached streptavidin molecules. This work helps to understand the interactions of kinesin-1 and obstacles on the microtubule surface. An interesting, possibly even more important side result is that this understanding will not only help to optimize transport assays, balancing speed and cargo-loading, but can be used as a novel method for the detection of proteins as well.
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.
The term biosensing relates to systems that include electronic, photonic, biologic, chemical and mechanical means for producing signals that can be used for the identification, monitoring or control of biological phenomena. The resulting biosensors are devices that employ biological components such as proteins to provide selectivity and/or amplification for the detection of biochemical materials for use in medical diagnostics, environmental analysis or chemical and biological warfare agent detection. Surface plasmon resonance (SPR) has become the technology of choice for label-free detection of proteins and other biomolecules. SPR is based on the excitation of a surface plasmon at the interface between a dielectric and a thin layer of metal, typically gold. Once the sample is covered with the nanostructured gold layer (or another suitable metal), the surface absorbs light at certain wavelength. The absorption maximum is influenced by the refractive index of the fluid at the gold surface. This effect is called localized surface plasmon resonance (LSPR) and it is used for detection of presence of biomolecules, such as specific proteins.
Much is being written about nanotechnology's role in vastly improving the detection and treatment of cancer. Detection of cancer at the earliest stage provides the greatest chance of survival. Unfortunately, cancer has a logarithmic growth rate. A one cubic centimeter size tumor may have 40-50 cell divisions and typically doctors don't see 80% of the life of a tumor. The detection of a protein pattern in blood serum can be helpful in evidencing a possible presence of cancer at an early stage. The problem is that 'early' means the capability of detecting very few molecules in dilute conditions. Now, in another step to improve the design and fabrication of devices for single molecule detection, new research has demonstrated an experimental capability of detecting down to as few as 10 organic molecules deposited on a quantum dot.
Carbon nanotubes (CNTs) have been widely used as electrodes for chemical and biological sensing applications and many other electrochemical studies. With their unique one-dimensional molecular geometry of a large surface area coupled with their excellent electrical properties, CNTs have become important materials for the molecular engineering of electrode surfaces where the development of electrochemical devices with region-specific electron-transfer capabilities is of paramount importance. It has been demonstrated that carbon nanotubes enhance the electrochemical activity of biomolecules and promote the electron-transfer reactions of redox proteins, such as myoglobin, cyctochrome c, and microperoxidase MP-11. The enhanced electrochemical activity and electron transfer rate at CNT electrodes have been widely believed to arise from the nanotube tips. However, no convincing experimental evidence has been obtained to prove that the CNT tip is more electrochemically active than its sidewall. Contradicting this common belief, researchers have now found that, surprisingly, the electrochemistry at carbon nanotube electrodes is not always facilitated by the nanotube tip. In fact, the relative electrochemical sensitivity of the nanotube tip and sidewall varies for different electrochemical probes proceeding with different reaction mechanisms.
One of the many fascinating concepts in nanotechnology is the vision of molecular electronics where tomorrow's engineers might use individual molecules to perform the functions in an electronic circuit that are performed by semiconductor devices today. This is just another example of scientists taking a cue from nature's playbook, where essentially all electronic processes, from photosynthesis to signal transduction, occur in molecular structures. The basic science on which molecular electronics technology would be built is now unfolding but researchers are still struggling with the most basic requirements for molecular electronics, for instance, how to precisely position individual molecules on a surface or how to reliably measure the resistance of a single molecule. A tremendous amount of painstaking work goes into developing the kind of ultraprecise and ultrasensitive instruments that are required to develop electronics at the nanoscale. A recent example is a new device for measuring the conductance values of single-molecule junctions which are covalently bound to two electrodes.
'Reverse engineering' is the process of discovering the technological principles of a device or system through analysis of its structure, function and operation, often by taking it apart and analyzing its workings in detail. This approach is a common practice among industrial companies who use it to analyze the competition's products, be it cars or MP3 players, to understand where the latest product improvements come from and how individual components are made. An increasing number of scientists apply a similar approach to nature's own 'micro- and nanotechnology' systems. They believe that learning from nature's designs and engineering successes is more likely to provide the cues for designing practical nanodevices than by simply applying a 'trial and error' approach. The basic idea is that natural materials and systems can be adopted for human use beyond their original purpose in nature. Some examples of 'reverse' biophysics work and have already proven quite useful, for instance the use of individual red blood cells as reliable, ultrasensitive mechanotransducers.
The phenomenon behind many color-based biosensor applications is the excitation of surface plasmons by light - called surface plasmon resonance for planar surfaces or localized surface plasmon resonance (LSPR) for nanoscale metallic structures. Surface plasmon resonance of metallic nanoparticles, in particular gold, has become a popular nanotechnology-enabled technique to build increasingly sensitive and fast biosensors. All the nanostructures used for the biosensing applications have two characteristics: Firstly, they contain certain recognition mechanisms specified to the analyte, for example antibodies or enzymes. Secondly, they are able to generate a distinguishing signal from the analyte and this signal could be generated by the nanostructures themselves or produced by signaling molecules immobilized or contained in the nanostructures. However, proper functionalization remains an issue when it comes to real-world applications, in particular, biological relevant samples such as membrane associated proteins and peptides.