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Imaging surface charges on individual biomolecules
RESEARCH NEWS
Imaging surface charges on individual biomolecules NANOTECHNOLOGY
Surface charges play a key role in determining the structure and function of proteins, DNA and larger biomolecular structures. For example, negatively charged DNA strands electrostatically interact with histone proteins, transcription factors, or polymerases thereby influencing the read-out of genetic information and the development of cancer. Similarly, the central process of protein folding and protein interaction, often governed by charges, is the major factor in protein-folding diseases such as Alzheimer’s or Parkinson’s Disease. However, thus far there have been no experimental methods to spatially resolve the electrostatic surface potential of individual biological molecules. In general, the investigation of individual molecules can shed light on their dynamic behaviour or on static heterogeneity which is masked in ensemble measurements. A collaborative effort between researchers from the London Centre of Nanotechnology [Leung et al., DOI: 10.1021/nl9012979] has led to the first measurements of the electrostatic surface potential of individual DNA and avidin molecules with nanometre resolution using Kelvin Probe Force Microscopy (KPFM) in air.
Atomic force microscope at London Centre for Nanotechnology
Kelvin Probe Force Microscopy (KPFM) can measure surface charges by contactless
recording of the electrostatic force between a conductive Atomic Force Microscope tip and a biomolecule on a support. To achieve this, the AFM tip is simultaneously excited at its mechanical resonance frequency and by an electrical (AC) voltage. This periodic electrical voltage on the tip leads to a force between the tip and the charges on the biomolecule, which is recorded by means of a lock-in amplifier and nullified by the Kelvin mode feedback by applying a separate DC voltage (not shown). The polarity and magnitude of this DC voltage corresponds to the local surface charge profile (in mV) which is recorded simultaneously with the topography of the biomolecule. The investigation led at the London Centre for Nanotechnology also show, for the first time, the surface potential of buffer salts shielding DNA molecules on a surface, which would not be possible with conventional ensemble techniques. It is anticipated that the ability to visualize the electrostatic surface potentials of individual proteins and DNA at molecular resolution will be an important tool in fundamental biophysical research and in the fields of biosensing and bio-nanoelectronics. Jonathan Agbenyega
How much risk do people think there is in nanotechnology? NANOTECHNOLOGY There has been a huge upsurge in anticipating how the public will react to nanotechnology, particularly a widespread negativity about its use and the possible health risks associated with nanomaterials. This has an important impact on those who regulate risks, as they need to understand emerging trends in public perceptions of this topic. A team of researchers from the universities of British Columbia and California analyzed a number of surveys undertaken to explore public perceptions of the risks and benefits inherent in the use of nanomaterials. Published online in Nature Nanotechnology (doi: 10.1038/NNANO.2009.265), they found that many in the nanoscience and policy communities are anxious to know whether or not this new class of technologies will be controversial. However, their study concluded that nearly half of those surveyed have no familiarity with nanotechnologies, despite their ever-increasing
presence in our lives. The results stressed that risk perceptions, which have an important consequence for policy making and public response and participation generally, have a very different character when studied outside the context of risk controversies, and also that it is a major challenge to those who study risk to find new methodological approaches to analyzing technology that is new to the public. As team member Terre Satterfield points out, “historically, technologies that are invisible, unknown, difficult to control, and undetectable to the human senses have all been judged by the public as highly risky. Nanotechnologies are all of these things and thus it should follow that they are seen by the public as risky.” Yet they found that those who currently perceive greater benefits outnumber those who perceive greater risks by 3 to 1. However, judgments about nanotechnologies are still highly malleable, as nearly 44% refuse to offer
any judgment, even if offered information on the subject. Satterfield reckons this is a good sign, as it suggests judgment conservatism or just good old waiting and seeing, a healthy outlook in times of high uncertainty. This is the first time researchers have tried to anticipate public response in advance, and it is reasonable to assume that prior theories of why people are averse to some technologies will be useful in anticipating responses to nanotechnologies. Especially since, when a product, or technology becomes stigmatized in the mind of the public, the economic consequences can be enormous, which happened in the UK with the sale and exportation of beef in the aftermath of the BSE crisis. From a health and safety policy point of view, sometimes people are very wise in their resistance to some new technologies. With nanotechnology, the case is still open.
Laurie Donaldson
OCTOBER 2009 | VOLUME 12 | NUMBER 10
11
Imaging surface charges on individual biomolecules NANOTECHNOLOGY
Surface charges play a key role in determining the structure and function of proteins, DNA and larger biomolecular structures. For example, negatively charged DNA strands electrostatically interact with histone proteins, transcription factors, or polymerases thereby influencing the read-out of genetic information and the development of cancer. Similarly, the central process of protein folding and protein interaction, often governed by charges, is the major factor in protein-folding diseases such as Alzheimer’s or Parkinson’s Disease. However, thus far there have been no experimental methods to spatially resolve the electrostatic surface potential of individual biological molecules. In general, the investigation of individual molecules can shed light on their dynamic behaviour or on static heterogeneity which is masked in ensemble measurements. A collaborative effort between researchers from the London Centre of Nanotechnology [Leung et al., DOI: 10.1021/nl9012979] has led to the first measurements of the electrostatic surface potential of individual DNA and avidin molecules with nanometre resolution using Kelvin Probe Force Microscopy (KPFM) in air.
Atomic force microscope at London Centre for Nanotechnology
Kelvin Probe Force Microscopy (KPFM) can measure surface charges by contactless
recording of the electrostatic force between a conductive Atomic Force Microscope tip and a biomolecule on a support. To achieve this, the AFM tip is simultaneously excited at its mechanical resonance frequency and by an electrical (AC) voltage. This periodic electrical voltage on the tip leads to a force between the tip and the charges on the biomolecule, which is recorded by means of a lock-in amplifier and nullified by the Kelvin mode feedback by applying a separate DC voltage (not shown). The polarity and magnitude of this DC voltage corresponds to the local surface charge profile (in mV) which is recorded simultaneously with the topography of the biomolecule. The investigation led at the London Centre for Nanotechnology also show, for the first time, the surface potential of buffer salts shielding DNA molecules on a surface, which would not be possible with conventional ensemble techniques. It is anticipated that the ability to visualize the electrostatic surface potentials of individual proteins and DNA at molecular resolution will be an important tool in fundamental biophysical research and in the fields of biosensing and bio-nanoelectronics. Jonathan Agbenyega
How much risk do people think there is in nanotechnology? NANOTECHNOLOGY There has been a huge upsurge in anticipating how the public will react to nanotechnology, particularly a widespread negativity about its use and the possible health risks associated with nanomaterials. This has an important impact on those who regulate risks, as they need to understand emerging trends in public perceptions of this topic. A team of researchers from the universities of British Columbia and California analyzed a number of surveys undertaken to explore public perceptions of the risks and benefits inherent in the use of nanomaterials. Published online in Nature Nanotechnology (doi: 10.1038/NNANO.2009.265), they found that many in the nanoscience and policy communities are anxious to know whether or not this new class of technologies will be controversial. However, their study concluded that nearly half of those surveyed have no familiarity with nanotechnologies, despite their ever-increasing
presence in our lives. The results stressed that risk perceptions, which have an important consequence for policy making and public response and participation generally, have a very different character when studied outside the context of risk controversies, and also that it is a major challenge to those who study risk to find new methodological approaches to analyzing technology that is new to the public. As team member Terre Satterfield points out, “historically, technologies that are invisible, unknown, difficult to control, and undetectable to the human senses have all been judged by the public as highly risky. Nanotechnologies are all of these things and thus it should follow that they are seen by the public as risky.” Yet they found that those who currently perceive greater benefits outnumber those who perceive greater risks by 3 to 1. However, judgments about nanotechnologies are still highly malleable, as nearly 44% refuse to offer
any judgment, even if offered information on the subject. Satterfield reckons this is a good sign, as it suggests judgment conservatism or just good old waiting and seeing, a healthy outlook in times of high uncertainty. This is the first time researchers have tried to anticipate public response in advance, and it is reasonable to assume that prior theories of why people are averse to some technologies will be useful in anticipating responses to nanotechnologies. Especially since, when a product, or technology becomes stigmatized in the mind of the public, the economic consequences can be enormous, which happened in the UK with the sale and exportation of beef in the aftermath of the BSE crisis. From a health and safety policy point of view, sometimes people are very wise in their resistance to some new technologies. With nanotechnology, the case is still open.
Laurie Donaldson
OCTOBER 2009 | VOLUME 12 | NUMBER 10
11