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Issue 2, 2005
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Monolayer-functionalized microfluidics devices for optical sensing of acidity

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This paper describes the integration of opto-chemosensors in microfluidics networks. Our technique exploits the internal surface of the network as a platform to build a sensing system by coating the surface with a self-assembled monolayer and subsequently binding a fluorescent sensing molecule to the monolayer. Fluorescent molecules were used that can switch between a fluorescent and a non-fluorescent state, depending on the acidity of the surrounding solution. Two systems were investigated. The first employs surface confinement of a Rhodamine B dye in a glass micro channel that serves as a molecular switch in organic solutions. Upon rinsing the micro channels with acidic or basic solutions it was possible to switch between the fluorescent and non-fluorescent forms reversibly. Moreover, this system could be used to monitor the mixing of two solutions of different acidity along the micro channel. To widen the scope of optical sensing in micro channels an Oregon Green dye derivative was immobilized, which functions as a sensing molecule for pH differences in aqueous solutions. In this case, a hybrid system was used consisting of a glass slide and PDMS channels. The fluorescence intensity was found to be directly correlated to the pH of the solution in contact, indicating the possibility of using such a system as a pH sensor. These systems allow real-time measurements and can be easily implemented in micro- and nanofluidics systems thus enabling analysis of extremely small sample volumes in a fast and reproducible manner.

Graphical abstract: Monolayer-functionalized microfluidics devices for optical sensing of acidity

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Publication details

The article was received on 01 Jul 2004, accepted on 09 Nov 2004 and first published on 26 Nov 2004

Article type: Paper
DOI: 10.1039/B409978H
Citation: Lab Chip, 2005,5, 163-170
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    Monolayer-functionalized microfluidics devices for optical sensing of acidity

    P. Mela, S. Onclin, M. H. Goedbloed, S. Levi, M. F. García-Parajó, N. F. van Hulst, B. J. Ravoo, D. N. Reinhoudt and A. van den Berg, Lab Chip, 2005, 5, 163
    DOI: 10.1039/B409978H

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