University of São Paulo: Researchers develop a method that can make sensor manufacturing cheaper

Researchers at the São Carlos Institute of Chemistry (IQSC) at USP have developed a new method that could make the manufacture of electrodes and sensors up to 66% cheaper. Experts proposed replacing an imported reagent (photoresist) used in the conventional process of building these devices, which can cost up to a thousand dollars per liter, for a laser-cut adhesive that guarantees high efficiency, but at a much lower cost. The innovative process can contribute to expand the production of electrodes used in several areas that require chemical analysis, such as pharmaceuticals, environment, agriculture and, mainly, diagnostics in health. An article describing the method was published in the scientific journal Electrophoresis.

The proposed method favors the manufacture of devices on a large scale, in addition to requiring less sophisticated equipment and laboratories than photolithography, a traditional technique used in the production of computer microchips. Laís Brazaca, a professor at IQSC and one of those responsible for innovation, explains that, until today, the production of electrodes usually requires large infrastructure, which is expensive and cannot be found anywhere in the country. According to the researcher, the specialized laboratory apt to manufacture equipment of the type closest to São Carlos, it is now about 150 kilometers (km) away, in Campinas.

“The use of the structure requires scheduling and research can suffer due to the high demand. In our work, I used technologies that exist at USP itself, which are easier to access, and we were able to produce the electrodes here in the city”, he celebrates. Even with manufacturing changes, the sensors remained effective and analysis results remained reliable. “In principle, any sensor with millimeter dimensions can be made with this new methodology. A larger number of laboratories throughout Brazil will be able to use these sophisticated procedures, but at a low cost”, describes the scientist.

What changes in practice?
In the traditional process, the photoresist is applied to the base of what will become the electrode, usually a glass. Then, a mold with the specific design desired for the sensor is placed on top of this base and both are exposed to ultraviolet (UV) light, which imprints the characteristics of interest on the part. The device then goes through a machine that deposits metal in steam in the region demarcated by the mold. Finally, the development process is carried out, keeping the metal only in the areas where the UV light has hit, finishing the sensor. With the new technique developed at USP, adhesives are laser cut and glued onto the glass, replacing the reagent used in the conventional method. The rest of the process is repeated until, at the end, it is enough to peel the adhesive from the base and the sensor is ready.

The innovation developed at USP was initially designed for the production of conductivity sensors, which measure, for example, the content of salts in samples based on variations in the electrical current that passes through the device. “The more salts a sample has, the greater the electric current that travels through the electrodes”, explains IQSC professor Emanuel Carrilho, one of the authors of the study. By interpreting these data, researchers are able to discover, for example, whether there are contaminants in a sewage treatment plant or even the amount of nutrients in a hydroponic plantation – when there is cultivation outside the soil.

The new methodology could also revolutionize other sectors, such as healthcare, optimizing diagnoses. An example would be the detection of the so-called dry eye syndrome, a disease caused by problems in the glands that produce tears, impairing the lubrication of the eyes. The disease, which affects about 18 million Brazilians, causes unpleasant consequences, such as redness, itching and discomfort due to the light. “Based on the conductivity analysis, the sensor can differentiate the tear of a person with the syndrome from a healthy tear,” emphasizes the professor Carrilho. To validate the method, Laís Brazaca – who already has other research in the area of ​​diagnostic sensors in her curriculum – produced healthy synthetic tears in the laboratory and others considered to be unregulated so that they could be evaluated by a prototype sensor developed with her technique: ” Those who have dry eye syndrome have a more concentrated tear, with more salt. Thus, the current increases”, he describes.

The project, which included the participation of undergraduate students from the Federal University of São Carlos (UFSCar) and the State University of North Carolina, in the United States, impressed international researchers and received an honorable mention (month of August) from the scientific magazine Electrophoresis. Victor Takekawa, a last-year student in the Biotechnology course at UFSCar, participated in the development of the project at USP through a Scientific Initiation. He says that he enjoyed being part of the work, as he had access to content that complements his curriculum. “I was very happy to be able to work with this team, it motivated me a lot. It is important that undergraduate students have the opportunity to participate in research, because in class we learn a lot of technique, but we also need to have contact with this practical part. I was even more proud of the result. I had no idea how huge this project was. I will take this experience with me for the rest of my life”, concludes the young man.