This paper develops a simple, cost-effective, fully Inkjet-printed flexible temperature sensor with easy fabrication steps using PiXDRO LP50 inkjet printer. The thermistor sensor employed a Poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT: PSS) as a temperature-sensitive layer with silver nanoparticles (AgNps) as a contact electrode. The sensor performance was evaluated on different dimensions and types of substrates. Epson Glossy paper with 255 μm thickness and Polyimide (Kapton HN) with 50 μm thickness were used over temperatures ranging from room temperature up to 50 °C and 90 °C for paper and Kapton substrates, respectively. The sensor developed over Glossy paper showed the best sensitivity of -1.67 %/°C in the chosen temperature range while the sensor showed +0.113%/°C on PI substrate.

This work introduces a wearable, highly sensitive human body temperature sensor. The proposed thermistor sensor employs a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as a temperature sensing layer and interdigitated electrodes (IDEs) from Silver nanoparticles deposited on Polyimide (PI) and Epson glossy paper substrates. The IDEs were patterned using inkjet printer Drop-on-demand PiXDRO LP50. The PEDOT:PSS layer was added by drop casting technique. The sensitivity of fabricated sensors was tested for different IDE number of fingers to investigate their response to the temperature range of 28–50 °C. The sensors performed linearly in the tested temperature range. Repeatability has been verified for five temperature measurement cycles. The achieved sensitivities are −1.462% /°C and −3.202%/°C for Epson paper and PI substrates, respectively. The sensor bendability results highlight the capability of the proposed sensor to be utilized for the wearable human body temperature reading.

Indium oxide octahedral nanopowders were obtained from an ionic precursor compound after an oxidation process conducted under a low-oxygen atmosphere. This method was found to produce contamination-free indium oxide nanomaterial with very similar morphological and crystalline properties to the one produced by vapor-phase transport, but at significantly lower temperatures and higher yield. The as-synthesized indium oxide was mixed to an organic vehicle and microdrop deposited to form a film bridging the interdigitated silver electrodes patterned on top of a flexible, polyimide (Kapton^®), substrate. The gas sensing properties of the flexible chemoresistors towards ammonia vapors, hydrogen, and nitrogen dioxide were investigated. It was found that these sensors were remarkably sensitive to nitrogen dioxide at a low operating temperature of 150 °C. These results are consistent with the performance of vapor-phase transport synthesized indium oxide octahedra sensors on rigid, ceramic substrates. Therefore, the results presented here pave the way for the mass production of inexpensive gas sensors onto flexible substrates via additive manufacturing.

Many sensors are developed over flexible substrates to be used as wearables, which does not guarantee that they will actually withstand being bent. This work evaluates the gas sensing performance of metal oxide devices of three different types, before and after having undergone automated, repetitive bending tests. These tests were aimed at demonstrating that the fabricated sensors were actually flexible, which cannot be taken for granted beforehand. The active layer in these sensors consisted of WO₃ nanowires (NWs) grown directly over a Kapton foil by means of the aerosol-assisted chemical vapor deposition. Their response to different H₂ concentrations was measured at first. Then, they were cyclically bent, and finally, their response to H₂ was measured again. Sensors based on pristine WO₃-NWs over Ag electrodes and on Pd-decorated NWs over Au electrodes maintained their performance after having been bent. Ag electrodes covered with Pd-decorated NWs became fragile and lost their usefulness. To summarize, two different types of truly flexible metal oxide gas sensor were fabricated, whereas a third one was not flexible, despite being grown over a flexible substrate following the same method. Finally, we recommend that one standard bending test procedure should be established to clearly determine the flexibility of a sensor considering its intended application.