Microlenses speed chemical detection

Scientists at Georgia Tech have discovered a way employing reusable hydrogel microlenses to detect trace amounts of substances in seconds.

The microlenses make use of the antibody-antigen binding, the same process used by the human immune system, to detect biological or chemical agents. When antibodies on the microlenses come into contact with the antigen they are set to detect, they bind, causing the lenses to swell and become less dense.

By projecting an image through the tiny lenses, scientists can view this swelling as a change in the microlens’ focal length. If the projected image is normally in focus, it goes out of focus when it comes into contact with the substance.

The process is reversible, allowing the same lenses to be reused

The team tested their system on its ability to detect biotin, a B-complex vitamin. To make the two-micrometer-wide microlenses, they coated the surface of a flexible polymeric hydrogel microsphere with the antigen biotin and aminobenzophenone (ABP), a photo-cross-linking agent, which is able to chemically attach to other molecules when exposed to UV light.

After binding the biotin with its antibody, researchers exposed it to UV light, causing the ABP to react with the antibody, attaching it to the microlens irreversibly and readying the microlenses.

When the lens is exposed to a solution that contains the antigen, it will compete for the binding site on the antibody. When the antigen and antibody bind, the lens swells and become less dense, changing its focus.

A device based on this technique could be cheaper and more portable than current hardware. It could have applications in healthcare for conducting on-site blood tests, or allowing authorities to rapidly detect and identify a toxic chemical in the event of a spill or terrorist attack.