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Posted: May 09, 2011

Multicolored fluorescent nanostructures show promise for cellular imaging

(Nanowerk News) Combining the unique optical properties and potential for surface functionality of silicon nanostructures with the electronic properties of quantum dots offers exciting prospects for biological and optoelectronic applications. In particular, silicon nanowires coated with metal nanoparticles are known to display enhanced optical properties that could be used as the basis for more-efficient, longer-lasting biological sensors.
Based on this approach, Yao He and colleagues at Soochow University and City University of Hong Kong in China have now prepared multicolored fluorescent nanostructures specifically for application in biological imaging ("Highly Luminescent Water-Dispersible Silicon Nanowires for Long-Term Immunofluorescent Cellular Imaging").
"Our highly fluorescent silicon nanowires exhibit excellent aqueous dispersibility, strong photoluminescence and ultrahigh photostability, making them superbly suitable for long-term, real-time immunofluorescent cellular imaging," says He.
Multicolored fluorescent quantum-dot-decorated silicon nanowires
All aglow: Multicolored fluorescent quantum-dot (QD)-decorated silicon nanowires (SiNWs) are easily prepared by a one-pot microwave-assisted synthesis. The as-prepared SiNWs are highly luminescent (see picture, left) and are well-suited to long-term immunofluorescent cellular imaging (see stability comparison, right). (© Wiley-VCH Verlag)
The researchers prepared their nanostructures by coating silicon nanowires with CdTe nanoparticles using a one-pot method involving microwave irradiation. By varying the reaction temperature and time, it was possible to prepare structures with green, yellow or red luminescence. Transmission electron microscopy observations revealed that the nanoparticles were highly crystalline, allowing them to act as quantum dots to enhance the luminescence of the nanowires. The surface also shows an abundance of carboxylic acid groups, allowing further functionalization with molecules such as the functional groups of proteins, which could be used as the basis for a protein biosensor.
He and his colleagues demonstrated the long-term photostability of the quantum dot-decorated silicon nanowires by comparing their luminescence to organic dyes and free-standing CdTe quantum dots. The fluorescence of the silicon nanowires remained at around 50% of the original intensity after 80 minutes of ultraviolet irradiation a vast improvement in stability compared with the other structures.
"In the future, we plan to systematically study the theory and application of the decorated silicon nanowires as well as the inherent chemical, physical and optical properties of the silicon nanowires and quantum dots themselves," says He. The researchers envisage that the quantum dot-decorated silicon nanowires could be used in a wide range of biological applications, including in vivo and in vitro imaging, multiplexed detection of cancer markers and DNA detection. A range of optoelectronic applications are also possible, such as solar cells and multicolored light-emitting diodes.
Source: Tokyo Institute of Technology
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