Schematic illustration of a hollow fiber. The chemiluminescent liquid in the core (yellow) is guided through the fiber, also with help of further hole structures (dark blue).

Processing
biological samples on a small substrate the size of a computer chip is
becoming a common task for biotechnology applications. Given the small
working area, however, probing samples on the substrate with light can
be difficult. To address this issue, Xia Yu and co-workers at the A*STAR
Singapore Institute of Manufacturing Technology have now developed an
optical fiber system that is able to deliver light to microfluidic chips
with high efficiency.

“Our
compact optical fibers are designed for use with high-throughput
detection systems,” says Yu. “They are ideal for use in
space-restrictive locations.”

A
common way of probing biological samples is by light. In this method,
the sample is excited by an external light source and the light emitted
in response is detected, which provides a unique fingerprint of the
substance. Conventional techniques are able to deliver light to samples
and probe the response, but they are not very efficient at probing a
small sample volume. A solution to this is to use optical fibers that
are able to guide light to small spaces. The drawback with this
technique, however, has been that it can be difficult to insert the
external probe light into the optical fiber with sufficient
efficiencies.

Yu
and her co-workers have now circumvented this problem by using optical
fibers with a hollow core (see image). The empty hollow core can be
filled with liquids—in this case, with chemiluminescent solutions. The
liquid is important to promote the transport of light through the core.
In addition, these solutions consist of two liquids that when brought
together initiate a chemical reaction that emits light. If such a
solution is placed directly within the hollow core the problem of
coupling light into the fiber is circumvented. This not only avoids
external light sources but also promotes an established technology.

“The
use of chemical luminescence is a common technique for a variety of
detection assays in biology,” says Yu. “By incorporating the emission
mechanism into optical fibers, we can use it as a light source for
sensing applications in microfluidics systems.”

First
tests for such sensing applications are already underway, although some
challenges remain. For example, there might be losses in the light
emitted by the fluid if the emitted light is not perfectly confined
within the fiber. Such problems can be solved through improved fiber
designs and an appropriate choice of materials, and applications of
these fibers for microfluidic systems are promising.

Chemiluminescence detection in liquid-core microstructured optical fibers

Source: A*STAR