Friday, December 25, 2009

Fluorescence Quenching Microscopy and Fluorescein Dye Coating Provide Cheap Method to Visualize Graphene say Northwestern University Researchers

A fluorescence quenching microscopy (FQM) image of graphene oxide (G-O) sheets on a glass substrate with a 30 nm thick fluorescein/PVP coating taken by a cheap consumer digital camera (Panasonic, DMC-FZ1). This image is representative of what can be seen by naked eye with FQM. Scale bar = 50 μm. The green background is from fluorescein emission.

Image credit: Northwestern University, Jiaxing Huang

Graphene based sheets have stimulated great interest due to their superior mechanical, electrical, and thermal properties. A general visualization method that allows quick observation of these single atomic layers would be highly desirable as it can greatly facilitate sample evaluation and manipulation, and provide immediate feedback to improve synthesis and processing strategies.

A Northwestern University team lead by assistant professor of materials science and engineering at the McCormick School of Engineering and Applied Science Jiaxing Huang and including Jaemyung Kim, Laura J. Cote, and  Franklin Kim report that graphene based sheets can be made highly visible at a low cost under a fluorescence microscope by quenching the emission from a fluorescein dye coating, which can be conveniently removed afterward by rinsing without disrupting the sheets. They report their findings in Visualizing Graphene Based Sheets by Fluorescence Quenching Microscopy

They developed a general method for visualizing graphene based sheets on arbitrary substrates by fluorescence quenching microscopy (FQM). The fluorescence quenching mechanism eliminates the need for special substrates and even allows the direct observation of graphene based sheets in solution. It offers unprecedented imaging flexibility for characterizing graphene based materials.

Current imaging techniques for graphene based sheets are time consuming and rely on the use of special substrates and costly instruments.  In contrast, the fluorescence quenching mechanism is no longer limited by the type of substrate. Graphene, reduced graphene oxide, or even graphene oxide sheets deposited on arbitrary substrates can now be readily visualized with good contrast for layer counting.

Direct observation of suspended sheets in solution was also demonstrated. The fluorescence quenching microscopy offers unprecedented imaging flexibility and could become a general tool for characterizing graphene based materials.

Images of mechanically exfoliated graphene on a SiO2/Si substrate taken by (a) AFM, (b) optical microscopy, and (c) FQM using PVP/fluorescein. All scale bars ) 10 μm.

 Image credit: Northwestern University, Jiaxing Huang

Utilizing the strong fluorescence quenching effect, graphene based, single atomic layer carbon sheets can be visualized with a common fluorescence microscope by applying a dye dope polymer coating. The dye layer can be easily removed by washing after imaging without disrupting the underlying sheets.

FQM works with a wide range of fluorescent materials and polymers including resist materials used in photolithography and e-beam lithography. This makes FQM compatible with microfabrication processes. Therefore, FQM could greatly broaden the scope of single layer device fabrication since it can image these 2D sheets on arbitrary substrates. FQM enables high throughput, high contrast evaluation of graphene based

Their results were recently published in the Journal of the American Chemical Society.

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