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Subdiffraction-Resolution Optical Measurements of Molecular Transport in Thin Polymer Films

Pahal, Suman and Raichur, Ashok M and Varma, Manoj M (2016) Subdiffraction-Resolution Optical Measurements of Molecular Transport in Thin Polymer Films. In: LANGMUIR, 32 (22). pp. 5460-5467.

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Official URL: http://dx.doi.org/10.1021/acs.langmuir.6b00527


The measurement of molecular transport within polymer films yields information about the internal structural organization of the films and is useful in applications such as the design of polymeric capsules for drug delivery. Layer-by-layer assembly of polyelectrolyte multilayer films has been widely used in such applications where the multilayer structure often exhibits anisotropic transport resulting in different diffusivities in the lateral (parallel to the film) and transverse (normal to the film) directions. Although lateral transport can be probed using techniques such as fluorescence recovery after photobleaching (FRAP), it cannot be applied to probing transverse diffusivity in polymer films smaller than the diffraction limit of light. Here we present a technique to probe the transport of molecules tagged with fluorphores in polymer films thinner than the optical diffraction limit using the modulation of fluorescence emission depending on the distance of the tagged molecules from a metal surface. We have used this technique to probe the diffusion of proteins biotin and bovine serum albumin (BSA) in polyelectrolyte multilayer films. We also studied the interdiffusion of chains in multilayer films using this technique. We observed a 3 order of magnitude increase in interdiffusion as a function of the ionic strength of the medium. This technique, along with FRAP, will be useful in studying anisotropic transport in polymer films, even those thinner than the diffraction limit, because the signal in this technique arises only from transverse and not lateral transport. Finally, this technique is also applicable to studying the diffusion of chromophore-labeled species within a polymer film. We demonstrate this aspect by measuring the transverse diffusion of methylene blue in the PAH-PAA multilayer system.

Item Type: Journal Article
Publication: LANGMUIR
Additional Information: Copy right for this article belongs to the AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, DC 20036 USA
Department/Centre: Division of Electrical Sciences > Electrical Communication Engineering
Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Division of Interdisciplinary Sciences > Centre for Nano Science and Engineering
Date Deposited: 05 Jul 2016 06:35
Last Modified: 05 Jul 2016 06:35
URI: http://eprints.iisc.ac.in/id/eprint/54133

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