Creating an Origami Sensor Array

Technological advancements often emerge at the confluence of market trends. This appears to be the case with the ultra-sensitive, multifunction sensor array, developed by the Technion-Israel Institute of Technology.

The rise of the Internet of Things, the growing role of printed electronics and the increasing number of technologies that mimic nature have all shaped the system’s development. One other factor, however, is in play: The need for greater sensing efficiency and performance.

As a result, the new e-nose/e-tongue sensing system aims to provide engineers with the means to cost-effectively, accurately and simultaneously identify and distinguish trace amounts of different physical and chemical stimuli.

The researchers see the system enhancing various application areas, enabling the monitoring of phenomena ranging from temperature and humidity to light and volatile organic particles.

Overcoming Existing Shortcomings

A key failing of traditional e-nose/e-tongue sensor arrays is that the sensors reside on a planar substrate, preventing some arrays from differentiating complex physical and chemical stimuli due to sensor crosstalk. Measures to counter this shortcoming often increase the complexity of the designs, which in turn raises cost.

Engineers have sought ways to circumvent these problems, but largely, the measures have proven unsatisfactory. For instance, designers have tried to enable traditional e-nose/e-tongue sensor arrays to perform pattern discrimination between chemical stimuli by linking the systems to time–space-resolved separation techniques, such as gas chromatography (GC).

This approach is unsuitable for distinguishing physical stimuli, such as temperature, and it lacks the agility to handle the timescale of some chemical processes, such as compound separation. GC often requires highly trained professionals, costly maintenance and sophisticated, expensive equipment.

New Materials

To take these sensor arrays to the next level, the Israeli researchers started developing a tunable conductive ink. The scientists synthesized the ink using a simple one-pot hydrothermal reduction of graphene oxide and dopamine. Dopamine is a catechol-derived molecule that mimics mussel-adhesive proteins.

Testing showed the ink to be compatible with a wide variety of common substrates—including aluminum foil, inkjet paper, nitrile rubber glass and commercially polyimide film—as well as biological materials such as skin and fingernails. The ink is also waterproof, which may enable use in applications demanding the monitoring of physiological variables.

The ink offers other advantages. It is affordable, works with mass production processes, disperses in environmentally-friendly organic solvents, possesses good adaptation and tailoring abilities, and interacts with substrates in a binder-free manner. Equally important, designers can tune the ink’s sensory responses for different stimuli by using different substrates.

Origami Electronics

The most intriguing aspect about the e-nose/e-tongue sensing system is its origami architecture. The concept enables the integration of a group of conductive ink-based sensors onto a paper substrate folded into a hierarchical configuration.

To create the array, researchers deposited conductive ink on alternating layers of the origami structure, creating the internal response indicators linked with wires. Folded in a zigzag pattern, the layers are sealed with tape to form a one- or two-sided array.

The two-sided array has two unsealed entrances, which directly expose the sensing area to stimuli. The one-sided array, on the other hand, has only one entrance. Because of the nature of the paper substrate, the researchers assumed that the layered configuration would be an effective blocking framework for permeable/diffusible stimuli.

Many stimuli simultaneously change, making discrimination between physical and chemical stimuli in complex environments difficult to accomplish with a sensor array based solely on chemical interactions. The researchers at the Technion-Israel Institute of Technology aim to overcome this hurdle with a pre-calibrated array of chemical and physical sensors made from a unique combination of materials.

The scientists suggest their design can expand to possess more characteristics. This might be achieved by adjusting the configuration of the origami or using other functional inks.