Tiny, reusable sensing chip

The proliferation of point-of-care testing, from at-home blood glucose meters to COVID-19 rapid tests, is accelerating and improving medical care. However, continuing to upgrade the sensing technology fueling the growth of these products is becoming increasingly challenging.

Some optical sensing chips, for example, contain nanostructures nearly as small as the biological and chemical molecules they’re searching for. The nanostructures improve the sensor’s ability to detect molecules, but their diminutive dimensions make it difficult to guide the molecules to the correct area of the sensor.

“It’s kind of like building a new racing car that’s more streamlined and therefore runs faster, but its door is made too small for the driver to enter the car,” says Peter Q. Liu, Ph.D., assistant professor of electrical engineering at the University at Buffalo School of Engineering and Applied Sciences.

Liu – along with Xianglong Miao, a Ph.D. candidate in his lab, and Ting Shan Luk, Ph.D., at the Center for Integrated Nanotechnologies, Sandia National Laboratories – created a new sensor taking aim at the problem.

Described in a study published in Advanced Materials, the sensor uses surface-enhanced infrared absorption (SEIRA) spectroscopy.

Spectroscopy is the study of how light interacts with matter. While infrared absorption spectroscopy has existed for more than 100 years, researchers are still trying to make the technology more powerful, affordable, and versatile.

These sensors work with light in the mid-infrared band of the electromagnetic spectrum, used by remote controls, night-vision goggles, and other products.

The new sensor consists of arrays of tiny rectangular strips of gold. Engineers dipped the strips in 1-octadecanethiol (ODT), a chemical compound they chose to identify.

Researchers added a drop of liquid metal – in this case, gallium – to serve as the sensor’s base. Then, they placed a thin glass cover on top to form a sandwich-like structure.

The design of the sensor, with its layers and cavities, creates what researchers call a nanopatch antenna, funneling molecules into the cavities and absorbing enough infrared light to analyze biological and chemical samples.

“Even a single layer of molecule in our sensor can lead to a 10% change in the amount of light reflected, whereas a typical sensor may only produce a 1% change,” Liu says.

After measuring the ODT, the researchers removed the liquid gallium from the sensor chip surface with a swab, allowing the sensor to be reused, making it more cost-effective than alternatives.

“The structure of our sensor makes it suitable for point-of-care applications that can be implemented by a nurse on a patient, or even outside the hospital in a patient’s home,” he says.

University at Buffalo https://www.buffalo.edu