ETH Zurich researchers have developed smart graphene paper for rapid pregnancy and COVID-19 tests

The ETH researchers Chih-Jen Shih, Leonard Bezinge, Daniel Richards and Andrew deMello (RTL) have pooled their expertise to develop a new approach to rapid medical testing. Credit: ETH Zurich / Martin Rütsche

Researchers at ETH Zurich have developed a new method to create more accurate and faster paper-based rapid tests that use smart graphene paper technology. The tests involve microfluidics, where aqueous solutions move through a paper test strip via capillary forces, with antibodies capturing target substances like virus particles and concentrating them at a specific location. The target substance is then made visible as a stripe through a staining system. However, visual assessment of the results can be difficult, prompting the researchers to develop a way to form conductive electrodes directly inside the paper test strip to make measurements more sensitive, faster and more accurate.

Combining Paper-Based Microfluidics with Electronic Measurement Techniques

The researchers' paper-based microfluidics combines simple and cost-effective techniques with electronic measurement techniques, providing analytical applications that can be performed in aqueous solutions for various applications. These applications range from blood biomarker monitoring by patients themselves to soil, air, and water sampling in the field and disease testing in remote parts of the world that can be performed in a matter of minutes.

Overcoming Conductivity Barriers

Previous attempts to equip low-cost paper chemistry with detection electrodes have been hindered by conductive materials' fundamental properties. Electrical conductors are barriers when it comes to the flow of sample and reaction mixtures in a paper strip. This limitation is overcome by the researchers through a combination of skills. From the Shih group, the knowledge to generate conductivity directly in the paper was used, while the deMello group's knowledge of microfluidic systems was utilized.

Converting Cellulose to Pure Carbon Using a Laser

The researchers used a laser to convert the cellulose that makes up the paper's sugar polymers into graphene. The conversion process decomposes the cellulose molecules into carbon, oxygen and hydrogen. Graphene is conductive, and clever tuning of the laser energy allows researchers to control the decomposition of cellulose to graphene in such a way that the cellulose's original porosity is preserved, and individual oxygen groups of the cellulose remain intact on the surface of the graphene areas. This interaction between oxygen groups and water molecules ensures wettability in the electrodes, making it practically on a par with the rest of the paper.

Practical Applications and Cost-effective Production

Shih and deMello have implemented the principle in practical applications and significantly simplified the production of analytical paper strips. It only takes 90 minutes to produce 176 sensors from one A4 sheet of paper, with a unit cost of just $0.02.

An Ideal Environment for Interdisciplinary Innovations

Shih and deMello credit ETH Zurich's environment as playing a crucial role in the invention's development. They are part of the Department of Chemistry and Applied Biosciences and are directly inspired by the cutting-edge research being done around them. The researchers have yet to determine how they will make their invention available to society and market it. Still, given the possible applications, a licensing model may make sense. They can rely on the ETH Zurich environment as people at ETH transfer have experience protecting intellectual property and negotiating licensing agreements.