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Open AccessArticle

Microscopic Characterization of Individual Submicron Bubbles during the Layer-by-Layer Deposition: Towards Creating Smart Agents

by Riku Kato 1,2 and Hiroshi Frusawa 2,*
Faculty of Pharmaceutical Science, Nagasaki International University, Huis Ten Bosch, Nagasaki 859-3298, Japan
Research Center for Materials Science and Engineering, Kochi University of Technology, Tosa-Yamada, Kochi 782-8502, Japan
Author to whom correspondence should be addressed.
Academic Editor: Navneet Soin
Materials 2015, 8(7), 4176-4190;
Received: 11 December 2014 / Revised: 13 June 2015 / Accepted: 29 June 2015 / Published: 8 July 2015
(This article belongs to the Special Issue Smart Materials)
We investigated the individual properties of various polyion-coated bubbles with a mean diameter ranging from 300 to 500 nm. Dark field microscopy allows one to track the individual particles of the submicron bubbles (SBs) encapsulated by the layer-by-layer (LbL) deposition of cationic and anionic polyelectrolytes (PEs). Our focus is on the two-step charge reversals of PE-SB complexes: the first is a reversal from negatively charged bare SBs with no PEs added to positive SBs encapsulated by polycations (monolayer deposition), and the second is overcharging into negatively charged PE-SB complexes due to the subsequent addition of polyanions (double-layer deposition). The details of these phenomena have been clarified through the analysis of a number of trajectories of various PE-SB complexes that experience either Brownian motion or electrophoresis. The contrasted results obtained from the analysis were as follows: an amount in excess of the stoichiometric ratio of the cationic polymers was required for the first charge-reversal, whereas the stoichiometric addition of the polyanions lead to the electrical neutralization of the PE-SB complex particles. The recovery of the stoichiometry in the double-layer deposition paves the way for fabricating multi-layered SBs encapsulated solely with anionic and cationic PEs, which provides a simple protocol to create smart agents for either drug delivery or ultrasound contrast imaging. View Full-Text
Keywords: microbubble; layer-by-layer; polyelectrolyte; electrophoresis; charge-reversal microbubble; layer-by-layer; polyelectrolyte; electrophoresis; charge-reversal
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Kato, R.; Frusawa, H. Microscopic Characterization of Individual Submicron Bubbles during the Layer-by-Layer Deposition: Towards Creating Smart Agents. Materials 2015, 8, 4176-4190.

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