Cheap and easy method coats microscopic particles in seconds


Rebecca Pool

Thursday, July 25, 2013 - 12:00

Australia-based researchers have developed a quick, one-step method to coat microscopic objects.

Professor Frank Caruso and colleagues from the Department of Chemical and Biomolecular Engineering at the University of Melbourne, found that a simple mixture of tannic acid and iron would self-assemble as thin films on substrates in the mixing solution.

The team has demonstrated the method on myriad surfaces including glass beads, planar gold substrates, even E. Coli bacteria, forming films and capsules of different sizes and shapes.

DIC, SEM, AFM and TEM images of the iron-tannic acid capsules: these films are potential candidates for biomedical and environmental applications.

“This one-step coating process involves the assembly of a simple mixture of tannic acid with trace iron,” Caruso tells Microscopy and Analysis. “Tannic acid is adsorbed onto a substrate surface with the iron ions then cross-linking with this polyphenol. The films are instantaneously deposited and the coating does not vary according to the substrate, making this approach very versatile.”

Differential interference contrast microscopy, AFM, SEM and TEM revealed the coatings are thicker and stronger than some alternatives fabricated via multi-step methods.

The researchers can also remove underlying substrates leaving thin films or hollow vessels of tannic acid and iron.

Altering the pH of the tannic acid-iron solution triggers film disassembly, providing potential for the timed release of substances held within a capsule.

“[We could make capsules from the coating materials to deliver therapeutics or for use in bio-imaging techniques such as PET and MRI,” says Caruso. “In environmental applications, the capsules could be used to sequester metal ions.”

Research is published in Science.

Caruso has been named in the Top 20 Material Scientists in the world by Thomson Reuters for citation impact in the last decade.

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