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Chlorophyll molecule acts as reversible switch
RESEARCH NEWS
Gliding bacteria drive rotary motor NANOBIOMECHANICS
Combining biological molecules with synthetic devices could produce efficient micromachines with novel functionality. However, building such systems requires effective interfacing between biological materials and inorganic microstructures. Japanese researchers have now built a working micromechanical device that integrates inorganic materials with living organisms, producing a bacteria-driven rotary motor [Hiratsuka et al., Proc. Natl. Acad. Sci. USA (2006) 103, 13618]. The motor was constructed by researchers from the National Institute of Advanced Industrial Science and Technology (AIST), Osaka City University, and the Japan Science and Technology Agency. The team chose the gliding bacterium Mycoplasma mobile to turn their 20 µm cogwheel-like SiO2 rotors around Si tracks. Biotinylated M. mobile cells are introduced into the circular tracks via straight channels leading from a central, square-shaped depression in the Si substrate. Channels are designed such that cells enter the tracks in an asymmetric manner, promoting clockwise motion. The cells’ movement is also controlled by selective
Microscale rotor docked on circular track. M. mobile cells enter the motor via the straight channel. (Credit: Yuichi Hiratsuka).
coating of the bottom of the Si grooves with a sialic-acid-containing glycoprotein (fetuin) on which the bacteria glide. Circling cells bind with a streptavidin coating on parts of the rotor that protrude into the circular tracks. As the bacteria continue to glide, they pull the rotor with them. Rotors start moving within a few minutes of M. mobile being introduced, generally at a rate of 1.5-2.6 rpm, though continuous rotations
were also recorded. Most rotors (84%, n = 51) turn clockwise. Continuously turning rotors occasionally reverse direction, implying that motion is driven by a few cells. This type of motor could be used as a micropump in lab-on-a-chip systems, replacing external pumps and pipes, suggests Yuichi Hiratsuka, now based at the Japan Advanced Institute of Science and Technology. “Alternatively, we may be able to construct electric generator systems that convert abundant energy – glucose in the body – into electric energy,” he says. Hiratsuka is interested in using biological motors to make microrobots, though they will not necessarily be powered by M. mobile. “Mycoplasma is just one example of a microorganism with interesting and potentially useful properties. For instance, there is a gliding bacterium that moves using energy provided by photosynthesis. Chlamyodomonas swim towards light (phototaxis) and Dictyostelium amoeba crawl towards a specific chemical substance (chemotaxis),” he notes. Paula Gould
Chlorophyll molecule acts as reversible switch NANOBIOMECHANICS Researchers from Ohio University have demonstrated reversible, multistep switching in a single chlorophyll molecule [Iancu and Hla, Proc. Natl. Acad. Sci. USA (2006) w, 13718]. The scanning tunneling microscope (STM) study also provides the first detailed images of chlorophyll-a. Chlorophyll-a is a relatively large plant molecule comprising a porphyrin head and a carbon-chain tail. The molecule changes shape (conformation) in the light-harvesting regions of plant leaves by bending its long phytyl tail. Given the link between shape-change and biological function, researchers are keen to learn how to control this conformational change. “Chlorophyll-a is a vital ingredient in the photosynthesis process and has the potential to be used in bio-solar cell fabrication for alternative energy generation,” says Saw-Wai Hla. “Understanding its physical and structural properties is the key to solving research problems in both areas.” Violeta Iancu and Hla deposited a submonolayer of spinach-derived chlorophyll-a (97% purity) onto a cleaned Au(111) surface under ultrahigh vacuum at
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room temperature. Low temperature (4.6 K) STM reveals a close-packed assembly of chlorophyll-a clusters with a unit cell length of 1.6 nm. Individual STM images show molecular conformation switching in chlorophyll-a molecules assemble headmolecule. (Credit: Saw-Wai Hla.) tail-head-tail within to manipulate smaller molecules, this is the first time clusters, with the long molecular axis aligned along that such a large organic molecule has been used as a [211] surface directions of the Au(111). Highmultistep switch. “Conformation changes of molecules resolution STM also shows that each molecule’s impact many chemical and biological functions. We porphyrin unit lies flat on the Au(111), while the now have a technique and knowledge to study – and phytyl group is folded on top. Phytyl chains are even induce – molecular conformation changes with supported above the surface by four CH3 groups. atomic precision,” Hla says. The researchers manipulated the molecules by Chlorophyll-a may be a suitable candidate for future injecting tunneling electrons from the microscope applications in medical electronics involving nanoscale tip into one of two specific locations, which provides devices and logic circuits, given the molecule’s multiple energy for bond rotation. They used this technique to switching behavior and biocompatibility, Hla suggests. switch between four conformations of chlorophyll-a, In the meantime, the researchers are using their STM each time bending the phytyl chain by 60º. technique to probe other biological molecules. While the Ohio University researchers and others have previously used STM to create two-stage switches, or
NOVEMBER 2006 | VOLUME 1 | NUMBER 4
Paula Gould
Gliding bacteria drive rotary motor NANOBIOMECHANICS
Combining biological molecules with synthetic devices could produce efficient micromachines with novel functionality. However, building such systems requires effective interfacing between biological materials and inorganic microstructures. Japanese researchers have now built a working micromechanical device that integrates inorganic materials with living organisms, producing a bacteria-driven rotary motor [Hiratsuka et al., Proc. Natl. Acad. Sci. USA (2006) 103, 13618]. The motor was constructed by researchers from the National Institute of Advanced Industrial Science and Technology (AIST), Osaka City University, and the Japan Science and Technology Agency. The team chose the gliding bacterium Mycoplasma mobile to turn their 20 µm cogwheel-like SiO2 rotors around Si tracks. Biotinylated M. mobile cells are introduced into the circular tracks via straight channels leading from a central, square-shaped depression in the Si substrate. Channels are designed such that cells enter the tracks in an asymmetric manner, promoting clockwise motion. The cells’ movement is also controlled by selective
Microscale rotor docked on circular track. M. mobile cells enter the motor via the straight channel. (Credit: Yuichi Hiratsuka).
coating of the bottom of the Si grooves with a sialic-acid-containing glycoprotein (fetuin) on which the bacteria glide. Circling cells bind with a streptavidin coating on parts of the rotor that protrude into the circular tracks. As the bacteria continue to glide, they pull the rotor with them. Rotors start moving within a few minutes of M. mobile being introduced, generally at a rate of 1.5-2.6 rpm, though continuous rotations
were also recorded. Most rotors (84%, n = 51) turn clockwise. Continuously turning rotors occasionally reverse direction, implying that motion is driven by a few cells. This type of motor could be used as a micropump in lab-on-a-chip systems, replacing external pumps and pipes, suggests Yuichi Hiratsuka, now based at the Japan Advanced Institute of Science and Technology. “Alternatively, we may be able to construct electric generator systems that convert abundant energy – glucose in the body – into electric energy,” he says. Hiratsuka is interested in using biological motors to make microrobots, though they will not necessarily be powered by M. mobile. “Mycoplasma is just one example of a microorganism with interesting and potentially useful properties. For instance, there is a gliding bacterium that moves using energy provided by photosynthesis. Chlamyodomonas swim towards light (phototaxis) and Dictyostelium amoeba crawl towards a specific chemical substance (chemotaxis),” he notes. Paula Gould
Chlorophyll molecule acts as reversible switch NANOBIOMECHANICS Researchers from Ohio University have demonstrated reversible, multistep switching in a single chlorophyll molecule [Iancu and Hla, Proc. Natl. Acad. Sci. USA (2006) w, 13718]. The scanning tunneling microscope (STM) study also provides the first detailed images of chlorophyll-a. Chlorophyll-a is a relatively large plant molecule comprising a porphyrin head and a carbon-chain tail. The molecule changes shape (conformation) in the light-harvesting regions of plant leaves by bending its long phytyl tail. Given the link between shape-change and biological function, researchers are keen to learn how to control this conformational change. “Chlorophyll-a is a vital ingredient in the photosynthesis process and has the potential to be used in bio-solar cell fabrication for alternative energy generation,” says Saw-Wai Hla. “Understanding its physical and structural properties is the key to solving research problems in both areas.” Violeta Iancu and Hla deposited a submonolayer of spinach-derived chlorophyll-a (97% purity) onto a cleaned Au(111) surface under ultrahigh vacuum at
18
room temperature. Low temperature (4.6 K) STM reveals a close-packed assembly of chlorophyll-a clusters with a unit cell length of 1.6 nm. Individual STM images show molecular conformation switching in chlorophyll-a molecules assemble headmolecule. (Credit: Saw-Wai Hla.) tail-head-tail within to manipulate smaller molecules, this is the first time clusters, with the long molecular axis aligned along that such a large organic molecule has been used as a [211] surface directions of the Au(111). Highmultistep switch. “Conformation changes of molecules resolution STM also shows that each molecule’s impact many chemical and biological functions. We porphyrin unit lies flat on the Au(111), while the now have a technique and knowledge to study – and phytyl group is folded on top. Phytyl chains are even induce – molecular conformation changes with supported above the surface by four CH3 groups. atomic precision,” Hla says. The researchers manipulated the molecules by Chlorophyll-a may be a suitable candidate for future injecting tunneling electrons from the microscope applications in medical electronics involving nanoscale tip into one of two specific locations, which provides devices and logic circuits, given the molecule’s multiple energy for bond rotation. They used this technique to switching behavior and biocompatibility, Hla suggests. switch between four conformations of chlorophyll-a, In the meantime, the researchers are using their STM each time bending the phytyl chain by 60º. technique to probe other biological molecules. While the Ohio University researchers and others have previously used STM to create two-stage switches, or
NOVEMBER 2006 | VOLUME 1 | NUMBER 4
Paula Gould