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Microscope detects biomolecules on the nanoscale

[size=5]Microscope detects biomolecules on the nanoscale[/size]Sk~&p4Z,jZC

lyyEt-z0U7q [b]【纳米科技世界快讯】A new way to detect biological molecules on the nanoscale has been developed by scientists in the US. The technique, which employs Kelvin probe-force microscopy, could offer a general approach to label-free biosensing with improved resolution, sensitivity and speed. It could be useful for detecting targets like DNA and proteins.[/b]
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z;d"{"y3LI`p Many traditional biodetection techniques rely on spectroscopically sensing a chemical label, such as a fluorescent dye, which is fixed onto the molecules of interest. Other label-free methods look for the changes caused when these targets bind, such as an increase in mass on a cantilever or charge on a surface. Since many biomolecules are charged, this last approach is particularly attractive and is already used in the scanning probe-based detection technique, Kelvin probe-force microscopy (KPFM).PTW0T([v

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[i]        Kelvin probe force microscopy with DNA arrays.[/i]
#X8|;E)RGfg{-f y [i]Top: A schematic view of a DNA template (blue) generatedby dip pen nanolithography (left) and a typical KPFM response (right)in which electrostatic potential is plotted against surface position.[/i]4zBGT s
[i]Bottom: on exposure to complementary strands of DNA (red),hybridization with appropriate spots takes place (left) leading to adrastic change in the KPFM response (right).[/i]3? KV-?:bC
[i]Credit: [/i][i]Nature Nanotechnology[/i]Il7jq:zCYb
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KPFM – also known as surface potential force microscopy or capacitive probing – has many advantages as a biomolecular detection technique. It can be carried out under ambient conditions, eliminating the need for a vacuum or special fluid cell. It is also a non-contact method, which means that it can be performed at high speeds, unlike other scanning probe techniques that do require contact with a substrate.a9Q z!u,p

&Cmk@rr#h h\ Now, Angela Belcher and Asher Sinensky of the Massachusetts Institute of Technology have applied KPFM to measure binding events on the nanoscale for the first time. The researchers achieved this by combining KPFM with another scanning probe method called dip-pen nanolithography to pattern biological molecules into arrays that are less than a micron across. The new method can be used to detect any charged molecule, says the team.
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B"^ j9i1D"l ?n] In their experiments, Belcher and Sinensky patterned single strands of DNA, which are negatively charged, onto gold substrates and measured their KPFM response. When complementary target DNA strands are placed on the surface of the single strands, the charge density in a given area doubles. This increase in the surface potential is then detected with KPFM. Um,U&\/v{dAI
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The technique, which employs a commercial atomic force microscope nanoprobe, has a high resolution of less than 10 nm, a high sensitivity of less than 50 nM and a high speed of greater than 1000 µm per second. It can therefore easily distinguish between single- and double-stranded DNA and can detect as few as three base-pair mismatches between anchored DNA strands and their target sequences. Indeed, the researchers were able to demonstrate the selective sensing of DNA sequences taken from anthrax and malaria genes using their method.
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I0a*r Xbq$d The work was published in [url=http://www.nature.com/nnano/journal/v2/n10/abs/nnano.2007.293.html][i]Nature Nanotechnology[/i] [b]2[/b] 653[/url].