Lab-on-a-chip to measure glucose in a single drop of sweat

Highly sensitive and rapid detection of blood glucose is a diagnostic necessity in medicine. For instance, lack of insulin and too much blood sugar are two main causes of diabetes, both of which can be detected by measuring blood glucose. Now, using fiber optics and microfluidics, researchers are developing a cheap, ultra-sensitive lab-on-a-chip device that can quickly measure glucose in just a drop of sweat.
The lab-on-a-chip device integrates a fiber optic biosensor with a microfluidic chip and detects glucose levels from droplets of sweat. It is shown here next to a Hong Kong dollar, which is the same size as a U.S. dollar coin.
Image credit: A. P. Zhang et al., The Hong Kong Polytechnic University

The team, from the Hong Kong Polytechnic University and Zhejiang University in China, is developing the device to help earlier diagnosis and prevention of diabetes.

The technology behind it belongs to a new field called “optofluidics” that brings together photonic sensing (using the properties of light to detect chemicals) and microfluidics (precise control of tiny amounts of fluid along microchannels)

What is unique about the new device, according to a paper in the Biomedical Optics Express, is that it uses fiber optic sensors to detect the glucose. Integrating this type of sensor into a microfluidic chip makes the device not only highly sensitive but also cheap and portable.

A. Ping Zhang, associate professor in the department of electrical engineering at the Hong Kong Polytechnic University, says photonic approaches are seen as one of the most promising techniques for ultra-sensitive sensing.

And when you integrate photonics with the tiny platform that microfluidic chips offer, you can make a small lab-on-a-chip analysis system for fast and reliable results.

Others have tried to integrate electrochemical glucose sensors into microfluidic channels to produce portable and low-cost microfluidic chips, but these have been plagued with problems, such as electroactive interference in the electrochemical sensors.

So the team turned to fiber optics, which are immune to electromagnetic interference, to get around the problem.

Fiber optic biosensor senses very low levels of glucose in solution

In their paper, Zhang and colleagues describe how they combined a new fiber optic biosensor with a microfluidic chip to create an interference-free optofluidic device for ultra-sensitive detection of glucose levels.

The fiber optic sensor they created is very sensitive to changes in the refractive index of the material that surrounds it. To transform it into a glucose monitor, the researchers used a film of glucose oxidase as a sensing material as it reacts with glucose in solution.

To both support the sensing film and further enhance the signal, the team incorporated layers of two other materials – polyethylenimine (PEI) and polyacrylic acid (PAA) – into the sensor. The result is several layers of PEI/PAA, with a top layer of glucose oxidase, that is then embedded in the microchannel of the chip.

Zhang says the PEI/PAA multilayer film “surveils the oxidation of glucose with the glucose oxidase catalyst and responds to the reaction via swelling or contracting.”

After running several tests, Zhang says they found the fiber optic sensor “is very sensitive on its own and can detect glucose oxidase concentrations as low as 1 nM (10-9 molarity),” but after they integrated it into the microfluidic chip, the sensor’s performance “remarkably further improved.”

The sensor improved not only in detection range, but also in response time, which “shortened from 6 minutes to 70 seconds,” note the researchers.

There was also no significant loss of biomolecular activity, suggesting that the method they used to create the sensor results in a “robust electrostatic absorption of glucose oxidase within the sensing film,” Zhang adds.

The device detects glucose in solution – so it could be used to measure glucose levels from just a tiny droplet of sweat.

Ultimately, the team aims to develop a range of multifunctional lab-on-a-chip devices for use in research and development in fields ranging from biomedical diagnostics to environmental monitoring and even drug discovery.