New technique discovered by scientists enables biologically active enzymes to survive the rigors of inkjet printing presenting a promising alternative to routine blood screening exams faced by diabetic patients. The KAUST-led team used this approach to make disposable devices that can measure glucose concentrations in human saliva.
Key to this approach is replacing traditional electronic circuitry in the sensors with low-cost plastics that can be manufactured quickly and in large quantities.
Bioscientist Sahika Inal collaborated with electrical engineer Khaled Salama and materials scientist Derya Baran to use inkjet technology to produce sensors sensitive to small sugar concentrations in biofluids.
"Paper is porous, which makes it challenging to print conducting and biological inks that are dissolved in water," says Eloise Bihar, a postdoctoral researcher at KAUST and the first author of the study. "Printing the enzyme is tricky as well--it's sensitive to variations of temperature, the voltage applied at the cartridge, and the pH of the ink."
After optimizing the enzyme-printing conditions, the researchers had another obstacle to tackle. While fluids, such as sweat or saliva, contain enough sugar for monitoring purposes, they also contain molecules, such as ascorbic acid, that interfere electrically with conducting polymers. Coating the sensor with a nafion polymer membrane that repels the negative charges present in most interfering species enabled measurement of only the relevant glucose levels in saliva samples from volunteers.
Experiments showed the top coating gave the sensor an unprecedented shelf life--the enzyme could be kept alive and active for a month if stored in a sealed bag. These results are encouraging the team to expand the capabilities of this approach by incorporating different enzymes into the sensing layer.
"Optimization never ends in engineering, so we are trying to make this system more robust to detect other metabolites in biofluids," says Inal.