Sensitive 3D Printed Sensors Can Measure Acetone Content in Breath, Making Life Easier for Diabetics

A collaborative team of researchers from Kiel University (CAU) in Germany and the Technical University of Moldova (TUM) used 3D printing to produce highly sensitive, energy-efficient sensors. This work could usher in a better way for diabetics to check their blood sugar levels that doesn’t involve pricking their finger with a needle, but instead simply breathing. The team recently explained their cost-effective method in a paper, titled “Facile fabrication of semiconductive oxide nanostructures by direct ink writing of readily available metal microparticles and their application as low power acetone gas sensors,” that was published in the journal Nano Energy.

Producing these kinds of sensors typically requires many steps, several hours, and a nearly dust-free environment. But the research team’s concept can 3D print multiple mixed metal oxide sensors at the same time, in just minutes, in normal, ambient air.

“In this work, a facile two-step fabrication and characterization of printed acetone sensors based on mixed semiconducting metal oxides is introduced. The devices are fabricated by Direct Ink Writing metal microparticle (MP) stripes of commercially available pure iron and copper particles onto the surface of a glass substrate, forming a bridging multi-phase semiconducting oxide net by subsequent thermal annealing,” the researchers explained in the abstract of their paper.

The open, porous structure of the semiconductor is what makes volatile organic compound (VOC) detection so sensitive. These sensors use a special structuring at the nano level to measure the concentration of acetone vapor, which, in the breath, corresponds with a human’s blood sugar levels.

“To make this special structure we heat simple microparticles of metal until numerous fine nanowires and nanospikes form on them,” said materials scientist Leonard Siebert, a doctoral research in CAU’s Functional Nanomaterials working group. “With a specially developed ink we can apply these particles with precision to various surfaces using a 3D printer.”

Graphical abstract

Its larger surface makes the sensor sensitive enough to be seen under a high-resolution electron microscope, where you can see that molecules of gas, such as acetone, can get tangled easily in a bunch of nanowires only 20 nm in diameter.

The researchers have learned that the starting metal material of the sensors can be “varied in a targeted manner,” which changes its structure and size, and allows for the gas detection that will make it so useful for diabetics.

Professor Rainer Adelung, head of the working group at Kiel University, stated, “This is still, first and foremost, basic research, but this principle could be used in the future to develop sensors for hydrogen or other explosive and hazard gases.”

In order to correctly form the special nanospikes and wires, the metal sensor particles need to be the right size, or it won’t work.

Dr. Oleg Lupan, a Humboldt fellow and researcher in TUM’s Biomedical Engineering department, explained, “The correct and high ratio between surface and volume is crucial.”

But, just because their large size makes the sensors adequately sensitive, it unfortunately makes them difficult to fabricate with conventional methods, like vacuum evaporation or spraying systems. Smaller particles can be applied to surfaces using these fabrication technologies, but the microparticles in this work are too big.

“For this reason, we considered to use 3D printers to apply the micro-particles. The knowledge of materials and devices of colleagues from the Technical University of Moldova and our experience in nanomaterials and 3D printing complement each other perfectly here,” Siebert said.

A high base resistance equals low-power, energy efficient sensors, which allows them to be mobile. While only a little electricity passes through the wires in the completed sensor, organic molecules react strongly to them, which in turn changes the sensor’s resistance and releases signals that are easily measured.

“So our sensors only use very little energy. This makes small portable measuring devices conceivable, too, which can be read directly via smartphone, for example,” explained Lupan.

The sensor surface under the microscope: the research team grows tiny wires and spikes from metallic microparticles that are particularly good at trapping gas molecules. (Image: Kiel University)

A person with type I or II diabetes has an acetone content of more than 2 particles per million air molecules (ppm) in their breath. The researchers report that their extremely sensitive 3D printed sensors can detect acetone values of under 1 ppm.

“The open, highly porous bridging structures consist of heterojunctions which are interconnected via non-planar CuO/Cu₂O/Cu nanowires and Fe₂O₃/Fe nanospikes. Morphological, vibrational, chemical and structural studies were performed to investigate the contact-forming Fe₂O₃–CuO nanostructures on the surface of the MPs. The power consumption and the gas sensing properties showed selectivity to acetone vapor at an operating temperature of around 300 °C with a high gas response of about 50% and the lowest operating power of around 0.26 μW to a concentration of 100 ppm of acetone vapor. The combination of the possibility of acetone vapor detection, the controllable size and geometry and their low power make these printed structures important candidates for next developments of accessible detection devices, as well as acetone vapor monitoring (even below 1 ppm),” the researchers wrote in their paper.

3D printing has been used numerous times to help treat and manage diabetes. This research team hopes that its 3D printed sensors can be used in portable breath tests that will allow diabetics to measure the acetone content of their breath on the go, instead of pricking their finger to ascertain their blood sugar level. This is just another example of one of the many ways 3D printing can be used to make our lives easier.

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(Source: Nanowerk)