nano 2007-12-17 10:11
Nanopores speed up humidity sensing
[color=Blue]【纳米科技世界快讯】Humidity sensing has stepped up a gear thanks to the use of nanoporous polymeric transmission gratings developed by researchers in the US. The high surface-to-volume ratio structures react swiftly to changes in relative humidity, which is good news for the medical sector[/color].
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"The intrinsic response time of our sensor is around 137 ms, which is fast enough for the management of patients undergoing anaesthesia or pulmonary function diagnostics," Tony Jun Huang of Pennsylvania State University told nanotechweb.org. "What's more, our device can be further improved by tuning the composition of the pre-polymer syrup."'H d$c3_M
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[color=DimGray]Scientists from Penn State's biofunctionalized NEMS Laboratory. (Image credit: Pennsylvania State University)[/color] dO
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The gratings are made according to a holographic photopolymerization process. A pre-polymer syrup containing TL213 liquid crystal is mixed and sonicated and then placed in between two glass slides separated by microbeads. To pattern the device, the sandwiched sample is exposed to two interfering 100 mW laser beams at a writing angle of 30° for 1 min and then post-cured under a white-light source for 24 h.P O V ol!e1d#nl^2Iz
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Huang's colleagues Jinjie Shi and Vincent Hsiao point out that the addition of a non-reactive solvent, such as acetone or toluene, to the pre-polymer syrup is critical to the formation of nanopores. During photopolymerization, the solvent phase separates from the photopolymer to form nanoscale droplets that evaporate and leave tiny voids throughout the grating.$\r)?8a7]@7TB
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To turn the polymer chip into a working device, the researchers place the grating in the beam path of a halogen light source and monitor transmission as a function of humidity. The adsorption and desorption of water molecules inside the structure's nanoporous regions modifies the refractive index of the material and provides the basis for detecting variations in relative humidity over time.
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Having shown that nanopores are useful in humidity sensing, the team is now looking to transfer its technology into polymer-based drug-delivery systems.