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Nano-patterned fibres shine more brightly
RESEARCH NEWS
Brushing up on sensors SENSORS
With colorimetric sensors, problems with selectivity and degradation give rise to stability issues. Jason Locklin and graduate student Kristen Fries at the University of Georgia, [Fries et. al., Chem. Commun., 2008 DOI: 10.1039/b818042c] have developed covalently bound polymer brushes that can bind metal ions when irradiated with UV light. When asked the motivation behind this research Locklin comments, “In the course of a concurrent project related to methods we are developing to move droplets using light, we have utilized ionic complexation as a way to amplify wettability changes. The work of Professor Dermot Diamond at Dublin City University has inspired us to use these polymer brushes as sensors. The bindings mentioned above are completely reversible, and can be switched using visible light.” Through a grafting-from approach, the number of functional groups present at a surface can be greatly enhanced through the three-dimensional arrangement of tethered polymer chains.
When the colorless spiropyran polymer film is irradiated with UV light and dipped into solution containing different metal ions, colorimetric selectivity is achieved.
This allows for a brush-like morphology, with extended chain conformations and high density of molecules in a limited area. The increased functionality can also be used to amplify the stimuli responsive nature of the polymer coating at a surface. Locklin comments, “The polymer brush geometry allows for an increase in functionality and high
density of molecules in a limited area. Tuning the microenvironment through copolymerization can lead to matrices with enhanced selectivity. Covalently bound polymer chains can also lead to sensors with improved stability. Using molecular switches that use light to trigger an active or a passive state allows for improved lifetime of the sensor. For example, it provides a simple way to recalibrate the sensor and account for any drift. The changes in wettability can be used to control the motion of fluids in microfluidic channels. We are currently using surface energy differences to mix different fluids using light as the control element.” Locklin went on to say, “Developing sensors that are reversible and also extremely sensitive is one potential challenge. The binding has to be sufficiently weak to achieve reversibility. We plan to pursue improved techniques to push the detection limit of the sensors, possibly by using fluorescence as detection strategy.” Jonathan Agbenyega
Nano-patterned fibres shine more brightly NANOTECHNOLOGY Organic light sources become steadily more important
NanoImprint Lithography (RT-NIL). This high-
in the growing field of optoelectronics. Especially
throughput method employs a rigid nanostructured
in the area of nanoscale optics, much research is
silicon template, which is applied with high pressure
devoted to one-dimensional nanostructures that
(about 260 MPa) onto the fibres, without the
are utilized as building units for nanoelectronics and
drawbacks of hot embossing that would deteriorate
photonics. Recently, Francesca Di Benedetto and
the optoelectronic properties by the incorporation of
colleagues from the Italian Institute of Technology,
oxygen into the fibres.
Lecce, and the Scuola Superiore ISUFI, Lecce, have
Furthermore, Di Benedetto and her group assessed the
succeeded in an approach to easily produce organic
optical properties of the nano-patterned fibres. They
nanofibres of conjugated aromatic polymers by means of electrostatic spinning and enhance their optical properties via nanoimprinting, [Nature
AFM view of a single, nano-patterned lightemitting polymer fibre after RT-NIL (the bar marks 3 micrometers, vertical scale = 2 micrometers)
Nanotechnology (2008) 3, 614.] “Among other nano-technologies, electrospinning and nanoimprinting are particularly interesting in the respect of mass production,” says Dario Pisignano, the corresponding author. “Both of them are able to process large quantities of materials in short times. Electrospinning may process large volumes of polymer solution in a continuous way. Nanoimprinting as patterning technology can work on relatively large areas, and continuous processing chains. Combining high-throughput nanofabrication approaches is
found clear evidence for an enhancement of the light output from the fibres which had undergone RT-NIL compared to those which hadn’t. “In addition, we found that they act as cylindrical waveguides in the
a unique way to make commercially interesting produced nanomaterials.” The method of electrostatic spinning can manufacture large quantities of polymers into fibres of submicrometer diameter through plastic stretching (typical diameters are about 400 nm). In this process, the more or less parallel orientation of the organic molecules within the fibre is promoted by the applied external field. Once the fibres are spun, they are nanopatterned by the technique of Room-Temperature
visible and near infrared range and, more important, patterning is a powerful method to tune and tailor the emission wavelength of the fibers,“ explains Pisignano. He sees these materials as promising candidates for nanoscale LEDs, sensors, catalysts and lasers. “Our very first next step will concern the realization of nanopatterned lasers. We are also interested in developing catalytic applications based on patterned nanofibers,” says Pisignano.
Michel Fleck
DECEMBER 2008 | VOLUME 11 | NUMBER 12
9
Brushing up on sensors SENSORS
With colorimetric sensors, problems with selectivity and degradation give rise to stability issues. Jason Locklin and graduate student Kristen Fries at the University of Georgia, [Fries et. al., Chem. Commun., 2008 DOI: 10.1039/b818042c] have developed covalently bound polymer brushes that can bind metal ions when irradiated with UV light. When asked the motivation behind this research Locklin comments, “In the course of a concurrent project related to methods we are developing to move droplets using light, we have utilized ionic complexation as a way to amplify wettability changes. The work of Professor Dermot Diamond at Dublin City University has inspired us to use these polymer brushes as sensors. The bindings mentioned above are completely reversible, and can be switched using visible light.” Through a grafting-from approach, the number of functional groups present at a surface can be greatly enhanced through the three-dimensional arrangement of tethered polymer chains.
When the colorless spiropyran polymer film is irradiated with UV light and dipped into solution containing different metal ions, colorimetric selectivity is achieved.
This allows for a brush-like morphology, with extended chain conformations and high density of molecules in a limited area. The increased functionality can also be used to amplify the stimuli responsive nature of the polymer coating at a surface. Locklin comments, “The polymer brush geometry allows for an increase in functionality and high
density of molecules in a limited area. Tuning the microenvironment through copolymerization can lead to matrices with enhanced selectivity. Covalently bound polymer chains can also lead to sensors with improved stability. Using molecular switches that use light to trigger an active or a passive state allows for improved lifetime of the sensor. For example, it provides a simple way to recalibrate the sensor and account for any drift. The changes in wettability can be used to control the motion of fluids in microfluidic channels. We are currently using surface energy differences to mix different fluids using light as the control element.” Locklin went on to say, “Developing sensors that are reversible and also extremely sensitive is one potential challenge. The binding has to be sufficiently weak to achieve reversibility. We plan to pursue improved techniques to push the detection limit of the sensors, possibly by using fluorescence as detection strategy.” Jonathan Agbenyega
Nano-patterned fibres shine more brightly NANOTECHNOLOGY Organic light sources become steadily more important
NanoImprint Lithography (RT-NIL). This high-
in the growing field of optoelectronics. Especially
throughput method employs a rigid nanostructured
in the area of nanoscale optics, much research is
silicon template, which is applied with high pressure
devoted to one-dimensional nanostructures that
(about 260 MPa) onto the fibres, without the
are utilized as building units for nanoelectronics and
drawbacks of hot embossing that would deteriorate
photonics. Recently, Francesca Di Benedetto and
the optoelectronic properties by the incorporation of
colleagues from the Italian Institute of Technology,
oxygen into the fibres.
Lecce, and the Scuola Superiore ISUFI, Lecce, have
Furthermore, Di Benedetto and her group assessed the
succeeded in an approach to easily produce organic
optical properties of the nano-patterned fibres. They
nanofibres of conjugated aromatic polymers by means of electrostatic spinning and enhance their optical properties via nanoimprinting, [Nature
AFM view of a single, nano-patterned lightemitting polymer fibre after RT-NIL (the bar marks 3 micrometers, vertical scale = 2 micrometers)
Nanotechnology (2008) 3, 614.] “Among other nano-technologies, electrospinning and nanoimprinting are particularly interesting in the respect of mass production,” says Dario Pisignano, the corresponding author. “Both of them are able to process large quantities of materials in short times. Electrospinning may process large volumes of polymer solution in a continuous way. Nanoimprinting as patterning technology can work on relatively large areas, and continuous processing chains. Combining high-throughput nanofabrication approaches is
found clear evidence for an enhancement of the light output from the fibres which had undergone RT-NIL compared to those which hadn’t. “In addition, we found that they act as cylindrical waveguides in the
a unique way to make commercially interesting produced nanomaterials.” The method of electrostatic spinning can manufacture large quantities of polymers into fibres of submicrometer diameter through plastic stretching (typical diameters are about 400 nm). In this process, the more or less parallel orientation of the organic molecules within the fibre is promoted by the applied external field. Once the fibres are spun, they are nanopatterned by the technique of Room-Temperature
visible and near infrared range and, more important, patterning is a powerful method to tune and tailor the emission wavelength of the fibers,“ explains Pisignano. He sees these materials as promising candidates for nanoscale LEDs, sensors, catalysts and lasers. “Our very first next step will concern the realization of nanopatterned lasers. We are also interested in developing catalytic applications based on patterned nanofibers,” says Pisignano.
Michel Fleck
DECEMBER 2008 | VOLUME 11 | NUMBER 12
9