Angewandte Chemie International Edition

Cover image for Vol. 57 Issue 5

Editor: Neville Compton, Deputy Editor: Frank Maass. Editor Emeritus: Peter Gölitz

Online ISSN: 1521-3773

Associated Title(s): Angewandte Chemie, Chemistry - A European Journal, Chemistry – An Asian Journal, ChemistryOpen, ChemPhotoChem, ChemPlusChem, Zeitschrift für Chemie

Press Release

Angewandte Chemie International Edition 2006, 45, 1446–1449
doi: 10.1002/anie.200503102

Nr. 06/2006

Telltale Swelling

Soft microlenses as biosensors: change in focal distance signals presence of analyte molecules

Contact: L. Andrew Lyon, Georgia Institute of Technology, Atlanta (USA)
Registered journalists may download the original article here:
Label-Free Biosensing with Hydrogel Microlenses

The word gel first brings to mind things like shower or hair gel; however, there are also gels with a defined shape, such as the comfortable gel pads on modern bicycle seats or soft contact lenses. In the future, microscale gel lenses could play a role as biosensors for analysis and diagnostics. Researchers at the Georgia Institute of Technology have developed microlenses that react by changing their focal distance when a target substance is present.

Gels consist of a three-dimensional cross-linked matrix into which a liquid is incorporated—like water in a hydrogel, for example. The team headed by L. Andrew Lyon produced tiny particles of an acrylic polymer that are deposited onto a suitable support as hemispherical hydrogel lenses. As a sample analyte for the microlenses to “recognize”, the researchers chose biotin, a small vitamin. So that the lenses would later react to biocytin (a water-soluble variant of biotin), Lyon and his co-workers proceeded as follows: In the first step, they attached biotin molecules to the surface of the lenses and also generated special, reactive “anchor sites”. In the second step, these prepared lenses were treated with biotin antibodies, which bind to the biotin molecules on the surface of the lens. In the third step, the lenses were irradiated with UV light. This leads to a strong bond between the bound antibodies and the anchor sites. This double binding of the antibodies results in stronger cross-linking of the gel matrix on the surface of the lens, which causes the gel to absorb less water, so it shrinks. The curvature of the lens changes as does the focal distance, which can be measured. The lens is now switched “on”. If a biocytin-containing sample comes into contact with such a lens, the biocytin forces the biotin that is anchored to the lens surface out of its binding sites on the antibodies and binds to them itself. The extra cross-linking of the matrix is removed, allowing the lens to take up water and swell. The curvature and focal distance return to their original states—the lens is now switched “off”. “In this biosensor system, the microlens simultaneously takes on the roles of antibody carrier, signal converter, and amplifier,” explains Lyon.

The sensitivity of the lenses can be controlled by changing the number of antibodies bound to the surface. Using an array of microlenses with differing sensitivities on one chip opens up possibilities for quantitative analysis.

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