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Posted: Jun 14, 2006

A novel approach for the design of fluorescent sensors

(Nanowerk Spotlight) Researchers in Germany report a novel approach for the design of environmental sensors based on fluorescence interference contrast (FLIC) of semiconductor nanocrystals near a reflecting silicon surface. Their method is based on nanocrystals incorporated into polymer layers grafted onto reflecting surfaces.
Dr. Leonid Ionov, first author of a recent paper titled "Fast and Spatially Resolved Environmental Probing Using Stimuli-Responsive Polymer Layers and Fluorescent Nanocrystals" (published in the April 26, 2006 online edition of Advanced Materials) and Dr. Stefan Diez, head of the Bionanotechnology group at the Max-Planck-Institute of Molecular Cell Biology and Genetics in Dresden, explained their findings to Nanowerk:
"Our novel approach is based on interference of fluorescent light near a reflecting surface. The intensity of the light emitted by the fluorescent nanocrystals depends on their distance from the reflecting surface. To fabricate such a sensor, we adsorbed CdSeS nanocrystals onto a thin poly-2-vynil pyridine layer chemically grafted to a silicon wafer. The polymer layer swells in appropriate solvents (ethanol) and thus leads to changes of the distance between nanoparticles and the reflecting silicon wafer."
The approach developed by Ionov and Diez, and fellow researchers from the Leibniz-Institute of Polymer Research in Dresden, and the Ludwig-Maximilians-Universität in Munich, allows the combination of high spatial resolution (intrinsic to optical microscopy) with high temporal resolution. The main advantages of this new approach are extreme instrumental simplicity, high spatial precision of the measurements and a fast signal response.
Schematic of the polymeric sensor. Hydrophobic nanocrystals are adsorbed on a stimuliresponsive polymer layer that was previously grafted onto a reflecting substrate. The nanocrystal–surface distance depends on the conformation of the polymer chains and changes in different solvents. The change in height is then reported by a variation in the detected fluorescence intensity. (Reprinted with permission from Wiley-VCH Verlag GmbH & Co KG)
"The developed approach can be used for the design of simple and cheap environmental sensors. Moreover, if the spatial information is not required, the system can be minimized to a light-emitting diode, a photodiode and an optical filter" says Ionov.
"We plan to continue the investigation of the behavior of fluorescent nanocrystals on the thin polymer films" Diez explains their ongoing research and future plans. "It will help in understanding the properties of polymer surface and their interaction with proteins and cells. The latter is of particular interest to our lab, where we aim to couple biological machineries to artificial surface in a controlled manner. Moreover, we foresee a large potential of nanocrystal- polymer films for the design of switchable optical devices."
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