Researchers from the Federal University of São Carlos (UFSCar) have discovered a way to use old leaves as sensors. The new technique effectively laser-prints the surface of the leaves, turning them into something entirely unexpected.
The new technique has been developed as an alternative to 3D printing as a means to more sustainable ways to make things like sensors. By using leaf litter as the raw material, a new innovative approach has now been found.
Creating sensors through 3D printing offers a combination of speed, design flexibility, and the ability to use waste as a substrate. This approach enables a circular economy mode, where materials typically discarded are repurposed as low-cost resources. However, even most 3D printers tend to rely on some form of raw plastic material to create objects.
What if one research group wondered if you could use natural waste products like leaves? To this end, a team of Brazilian researchers, led by Bruno Janegitz, a professor at the Federal University of São Carlos (UFSCar), and Thiago Paixão, a professor at the University of São Paulo (USP), has presented a highly creative solution.
Turning fallen leaves into sensors
After years of study, they found a way to print electrochemical sensors on fallen tree leaves.
“We used a CO2 [carbon dioxide] laser to print the design of interest on a leaf by means of pyrolysis and carbonization. We thereby obtained an electrochemical sensor for use in determining levels of dopamine and paracetamol. It’s very easy to operate,” explained Janegitz.
“A drop of the solution containing one of these compounds is placed on the sensor, and the potentiostat to which it’s coupled displays the concentration,” Janegitz added.
To put it simply, a laser beam is used to burn a leaf in a process called pyrolysis. This process converts the cellulose in the leaf to graphite, which is then printed onto the leaf in a shape that can function as a sensor.
During the manufacturing process, different parameters of the CO2 laser are adjusted, such as the laser power, pyrolysis scan rate, and scan gap, to achieve the best possible results.
“The sensors were characterized by morphological and physicochemical methods, permitting exhaustive exploration of the novel carbonized surface generated on the leaves,” added Janegitz.
Ultra-natural sensors
“Furthermore, the applicability of the sensors was confirmed by tests involving the detection of dopamine and paracetamol in biological and pharmaceutical samples.” he stated.
Janegitz explained that for dopamine, the system had proven efficient in a linear range of 10–1,200 micromoles per liter, with a detection limit of 1.1 micromoles per liter. Additionally, for paracetamol, the system worked well in a linear range of 5-100 micromoles per liter, with a detection limit of 0.76.
In proof of concept tests involving dopamine and paracetamol, electrochemical sensors from fallen tree leaves demonstrated satisfactory analytical performance and noteworthy reproducibility, highlighting their potential as an alternative to conventional substrates.
Using fallen tree leaves instead of conventional materials results in significant cost-cutting and is environmentally sustainable.
Janegitz concluded that the leaves would likely have been incinerated or composted had they not been used as a substrate for high value-added devices. He emphasized that using the leaves in this way marked a major advancement in the fabrication of next-generation electrochemical sensors.
You can view the study in the Sustainable Chemistry and Engineering journal.