Gel lenses, resembling microscopic contacts, could find a role in biosensors for analysis and diagnostics, according to researchers at the Georgia Institute of Technology. They have developed a material that can be shaped into a microlens that changes shape, and so focal length, when a target substance is present.

Andrew Lyon and colleagues produced tiny particles of an acrylic polymer which they deposited onto a support material to form hemispherical gel lenses. The team tested the effect of a common biochemical, biotin, as a sample analyte. They first attached biotin molecules to the surface of the lenses. 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 ultraviolet light. This leads to a strong bond between the bound antibodies and the anchor sites. This double binding of the antibodies results in strong cross-linking of the gel matrix on the surface of the lens, which causes the gel to absorb less water, so it shrinks.

This shrinking changes the lens' focal length, which can be measured easily. The lens is now in the switched "on" state. If a sample containing biotin in its dissolved form, biocytin, comes into contact with the 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. This unlocks the surface cross-linking, the lens quickly absorbs water and swells, and its focal length changing radically as it does so. "In this biosensor system, the microlens simultaneously takes on the roles of antibody carrier, signal converter, and amplifier," explains Lyon.

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

Angew Chem Int Edn 2006, 45, 1446, http://dx.doi.org/10.1002/anie.200503102

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