Pen-like sensor detects bisphenol-A in water quickly and inexpensively

Researchers at the University of São Paulo have developed a portable device made from graphite, silver particles and polyurethane that detects BPA, a chemical compound harmful to health and considered an indicator of the presence of emerging pollutants in river or tap water.

By Karina Ninni  |  Agência FAPESP – Researchers affiliated with the University of São Paulo’s São Carlos Physics Institute (IFSC-USP) and São Carlos Chemistry Institute (IQSC-USP) in Brazil have developed a sensor with an elongated cylindrical shape similar to a pen for use in analyzing chemical pollutants in tap and river water. Made of graphite, silver nanoparticles and polyurethane, the sensor detects bisphenol-A (BPA), a chemical compound considered to be a molecular marker of the presence of emerging contaminants such as pharmaceuticals, hormones and pesticides, among others.

Emerging pollutants are compounds recently identified as dangerous to the environment and human health. They are called “emerging” in acknowledgment of rising levels of concern about them.

An article describing the research, which is funded by FAPESP, is published in Materials Science and Engineering: C.

Paulo Augusto Raymundo-Pereira, last author of the article, explained that some of the most dangerous chemical pollutants ejected into the environment are endocrine disruptors, substances that interfere with natural hormones and can have adverse effects on human health long after exposure has ceased. One such substance is BPA, widely used in the production of polycarbonate plastic, and in inner coatings of aluminum cans for food and beverages.

Even low levels of these substances can interfere with endocrine systems, which comprise a number of glands responsible for synthesizing hormones, causing such health problems as hormone imbalance, infertility, and cancer in reproductive organs. 

Brazil has banned imports and manufacturing of baby bottles and other infant utensils that contain BPA, given that babies are particularly susceptible to its harmful effects. A rule in effect since January 2012 prohibits the sale of polycarbonate baby bottles. In the United States, the Food and Drug Administration (FDA) banned the production of BPA-containing baby bottles in the same year. 

BPA is allowed in all other applications, but the legislation sets an upper limit for specific migration of BPA into food, determined on the basis of toxicological studies.

“It so happens, however, that factory waste may find its way into rivers and is hard for wastewater treatment plants to eliminate completely, so that it can find its way to the taps in our homes and be consumed by us,” Raymundo-Pereira explained. 

Water quality must be monitored uninterruptedly, of course. Emerging pollutants are currently detected by procedures involving collection and analysis of samples. In the case of BPA, detection requires costly and time-consuming techniques such as chromatography and spectroscopy.

“There isn’t a simple way to detect emerging pollutants. This is perhaps the main reason why BPA tests aren’t available to sanitation companies and environmental control agencies, or at least not to public services in developing countries. The situation may change if a sensitive and robust sensor in a simple, inexpensive device can do the job,” he said.

Pen sensor

The choice of materials for the pen sensor took into account the advantages obtained by combining them, such as stability, the ease with which the surface can be cleaned, simplicity, and low production cost. In addition, the type of polyurethane used is derived from castor oil and not harmful to the environment.

“We had prior experience with the selected materials,” Raymundo-Pereira said. “Graphite is a good electrical conductor. We knew silver nanoparticles would improve its conductivity still further while working very well in terms of detecting phenolic compounds such as bisphenol and also preventing other substances from ‘sticking’ to the sensor.”

To detect BPA, an electrical signal is produced by oxidation and/or reduction, chemical reactions that occur on the surface of the sensor when it comes into contact with the sample. Sensor-based methods can also be used in wastewater treatment plants to furnish rapid and reliable results without requiring sample collection, sophisticated equipment or trained personnel.

Innovative and versatile

Raymundo-Pereira explained that both the design and composition of the sensor are highly innovative. “It can be used as an alternative to traditional techniques, which are expensive and time-consuming, generate residues, and require high-level technical expertise,” he said. “Our device can be used by anyone without any training. It’s coupled to a pocket-sized analyzer and can be connected to a smartphone. This portability means it can be used in a treatment plant, for example, without the need to take a sample of the wastewater there to a laboratory for analysis.”

It can also be used in a river or stream, container, well or tap. “The result appears less than a minute after the sensor makes contact with the sample. Conventional tests take weeks or even months. The pen can also be used in a vertical position, but with the sensor facing up, and in this case, a sample comprising no more than 25 microliters [μl], or the equivalent of half a drop of water, is sufficient for the device to detect the substance,” said Marina Baccarin, first author of the article.

The group recently filed for a patent on the sensor from INPI, Brazil’s patent office, via the University of São Paulo’s innovation agency. “The technology is ready to be produced and transferred,” Baccarin said. “We used inexpensive materials and avoided sophisticated or imported equipment. Everything can be purchased in Brazil. Our goal was to facilitate technology transfer.”

FAPESP supported the research via three projects (16/01919-6, 17/04211-7, and 18/22214-6).

The article “Pen sensor made with silver nanoparticles decorating graphite-polyurethane electrodes to detect bisphenol-A in tap and river water samples” is at: www.sciencedirect.com/science/article/pii/S0928493120308730.