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Wearable, flexible, lightweight, and large-area electronics, able to adapt to arbitrary shapes, is a recent technology that promises to integrate sensing and data processing capabilities into everyday objects. This will allow connecting the digital and the physical worlds we live in and enable new innovative applications such as intuitive interfaces and smart textiles for continuous health and safety monitoring. Different technologies, including devices based on organic semiconductors and conventional silicon, are used to develop such wearable systems, however, devices made from novel oxide-based semiconductors currently have one of the best changes to result in electronic systems with sufficient electrical performance on flexible and large-area substrates. Yet, these exciting possibilities come at a price. If all the objects and surfaces around us are equipped with electronic sensor systems, these objects themselves transform into electronic devices, which in turn would massively increase the amount of electronic waste at the end of their lifetime. The same is true for plastic waste as currently most unobtrusive electronics are fabricated on polymer substrates. Furthermore, electronics that are operated near the human body must be safe and biocompatible. The perfect solution for these problems would be to fabricate electronics using environmentally friendly materials and processes, and to guarantee that the electronic components, after fulfilling their intended task, dissolve into their basic constituents, which are then entirely passive or safely absorbed into the nutrient cycle of our environment. Such transient and bioresorbable behavior has been demonstrated for several types of devices but is an underdeveloped approach in the field of oxide semiconductors. Here, motivations and challenges to combine the excellent electrical and mechanical properties of flexible oxide electronics with the environmental friendliness of bioresorbable electronics are explored. This is done by using the most important active building block of such electronics, namely, the TFT, as a model device (Figure 1). Besides assessing the various definitions of biocompatibility and environmental friendliness used in today’s research, the available classes of suitable materials and their impact in the electrical and environmental domain are described. Finally, an evaluation of how such materials can be integrated into working oxide transistors and which performance levels are achievable by these first examples of sustainable oxide TFTs is presented.

In this work, we present a novel, sensitive, easy-to-fabricate, flexible amperometric sensor constituted by screen-printed silver (Ag) electrodes functionalized with a copper (Cu) film electrodeposited on top of a spray coated network of single-walled carbon nanotubes (SWCNTs). The Cu/SWCNTs/Ag electrode showed excellent catalytic activity towards the electro-reduction of nitrate ions at neutral pHwith a significant increasein cathodicpeak currents incomparison with the electrode without SWCNTs (Cu/Ag). The developed Cu/SWCNTs/Ag sensor showed a wide linear detection range from $0.5~ \mu \rm{M}$ to 6.0 mM (0.31 mg/l to 372.02 mg/l) with good sensitivity (18.39 $\mu$ A/mM) and a calculated limit of detection (LOD) of 0.166 nM(10.29 $\mu$ g/l). It also showed a good selectivity (maximum standard deviation (SD) was 3.25 $\mu$ A) towards different interfering ions (Fe2+, Na+, Cu2+, SO2−4, CH3COO−, Cl−, NO−2 and HCO−3), as well as good reproducibility,mechanical durability, time and temperature stability. In real sample analysis (tap and river water), the sensor exhibited good agreement with the compared outcome of high-performance liquid chromatography (HPLC) measurements, proving to be a promising analytical tool for the detection of nitrate in water.

Electrochemical biosensors are widely investigated as they represent attractive analytical tools for detection of a broad range of bio-molecules, thanks to their simplicity, high sensitivity and short response time. Especially, biosensors employing an electrolyte-gated field-effect transistors (EG-FETs) as electrochemical transduction element have gained increasing interest, due to the signal amplification and the intrinsic low voltage range of operation. In this work we report the fabrication of flexible EG-FETs using spray-deposited semiconducting carbon nanotubes (CNTs), with a specific focus on the optimization of the CNT channel to optimize the performance of the resulting CNT-based EG-FET (EG-CNTFET). The transfer and the output characteristic of different devices with varying spraying parameters were tested, finding out that only devices with source-drain resistance of about ≤10 $\text{k}\Omega $ showed proper EG-CNTFET operation: for these devices we recorded a typical p-type behavior with an on–off ratio of 214 A/A up to 469 A/A (depending on number of the spray-deposited CNT layers). The fabricated EG-CNTFETs were functionalized with anti-spermidine antibodies to detect polyamine spermidine - a well-known chemical indicator of food quality. To ensure controlled immobilization and at the same time to preserve the electrical properties of the nanotubes, the spray-deposited films were modified with a bifunctional molecule, which attaches to the CNT via non-covalent ${\pi -\pi }$ interactions and leaves a free NHS-ester group for amide coupling of the antibodies. The fabricated EG-CNTFET-based immunosensors showed a linear detection range for spermidine from 10−3 to 102 nM, with the sensitivities ranging from −1.03 to $- 2.45\,\,\mu \text{A}/$ decade.