The Internet of Things (IoT) has revolutionized the requirements for sensors and smart devices, where high performance, power efficiency and low manufacturing costs are mandatory. As a consequence, the research for better performing materials and more cost-effective manufacturing techniques is being performed. This work reports on ink formulations based on nitrogen-doped graphene and environmentally friendly polymers (Polyvinylpyrrolidone (PVP) and Carboxymethyl cellulose (CMC), and their use in fully screen-printed transistors and humidity sensors. The ink formulations were developed using environmentally friendly solvents and showed non-Newtonian behaviour. The N-rGO composites showed a high electrical conductivity of 1.9 ± 0.5 S∙cm−1, 100 times higher than the reduced graphene oxide (rGO) composites. Fully printed Graphene field effect transistors (GFET) were developed with low operating voltage of < 2 V to be implemented as humidity sensors with the fully a linear response and high sensitivity (4.25 Ω∙%RH−1 as resistive sensor), allowing integration into low-power microcontrollers for sensing applications

This report explains the process of fabricating a flexible chemical sensor on a Polyethylene terephthalate (PET) substrate by using screen-printing technology. The sensor was tested for its response to body fluid (saliva) using Electrochemical Impedance Spectroscopy (EIS). The experiments show that the sensor is capable of differentiating between water and saliva, and it can be used for identifying body fluids., i.e., distinguishing between saliva or water, and detecting personal biomarkers present in the physiology

This study presents a novel silver nanoparticle ink formulation designed for inkjet printing applications using terpineol as an eco-friendly solvent and butylamine as a stabilizer to ensure stability, high conductivity, and compatibility with inkjet technology. Silver nanoparticles were synthesized using a modified one-pot method in the presence of highly effective stabilizers and surface modifiers such as oleic acid and oleylamine, resulting in uniform particles of less than 10 nm in size, which were then dispersed in a mixture of terpineol and butylamine. The resulting ink demonstrated exceptional stability over 85 days, maintaining optimal rheological properties for inkjet printing. The ink exhibited a perfect jetting performance. We were able to obtain silver conductive patterns reaching 81% of bulk silver conductivity. These results highlight the ink’s promise for scalable, sustainable manufacturing, combining environmental advantages with high-performance functionality.

Compliant vibrating soft actuators made with dielectric elastomer actuators are successfully assembled with mechanical energy harvesters, which operate a few hundred volts. The TENG-DEA module as a sensor-actuator fusion is applicable to wearable haptic systems, which are self-powering as well as sensing mechanical touches. The modules provide a solution for compliant and lightweight energy-generating, sensing and actuation functions to wearable haptic systems.

The transition to a sustainable society is driving the development of green electronic solutions designed to have a minimal environmental impact. One promising route to achieve this goal is to construct electronics from biobased materials like cellulose, which is carbon neutral, non‐toxic, and recyclable. This is especially true for internet‐of‐things devices, which are rapidly growing in number and are becoming embedded in every aspect of our lives. Here, paper‐based sensor circuits are demonstrated, which use triboelectric pressure sensors to help elderly people communicate with the digital world using an interface in the form of an electronic “book”, which is more intuitive to them. The sensors are manufactured by screen printing onto flexible paper substrates, using in‐house developed cellulose‐based inks with non‐hazardous solvents. The triboelectric sensor signal, generated by the contact between a finger and chemically modified cellulose, can reach several volts, which can be registered by a portable microcontroller card and transmitted by Bluetooth to any device with an internet connection. Apart from the microcontroller (which can be easily removed), the whole system can be recycled at the end of life. A triboelectric touch interface, manufactured using printed electronics on flexible paper substrates, using cellulose‐based functional inks is demonstrated. These metal‐free green electronics circuits are implemented in an “electronic book” demonstrator, equipped with wireless communication that can control remote devices, as a step toward sustainable and recyclable internet‐of‐things devices.

Wood is an inherently hygroscopic material which tends to absorb moisture from its surrounding. Moisture in wood is a determining factor for the quality of wood being employed in construction, since it causes weakening, deformation, rotting, and ultimately leading to failure of the structures resulting in costs to the economy, the environment, and to the safety of residents. Therefore, monitoring moisture in wood during the construction phase and after construction is vital for the future of smart and sustainable buildings. Employing bio-based materials for the construction of electronics is one way to mitigate the environmental impact of such electronics. Herein, a bio-graphene sensor for monitoring the moisture inside and around wooden surfaces is fabricated using laser-induced graphitization of a lignin-based ink precursor. The bio-graphene sensors are used to measure humidity in the range of 10% up to 90% at 25 °C. Using laser induced graphitization, conductor resistivity of 18.6 Ω sq−1 is obtained for spruce wood and 57.1 Ω sq−1 for pine wood. The sensitivity of sensors fabricated on spruce and pine wood is 2.6 and 0.74 MΩ per % RH. Surface morphology and degree of graphitization are investigated using scanning electron microscopy, Raman spectroscopy, and thermogravimetric analysis methods. © 2023 The Authors. 

Our present work focuses on the development of nickel oxalate (NiOX) template-assisted growth of a nickel-metal organic framework (Ni-MOF) with sheetlike morphology on carbon paper (CP) electrode for the noninvasive detection of glucose. We have utilized an extended gate field effect transistor (EGFET) where the Ni-MOF/CP electrode serves as the extended gate of a commercial n-type metal oxide semiconductor FET for sensing glucose. The electrode detects glucose concentrations ranging from 20 μM to 1.47 mM. The sensor operates at a voltage of 0.7 V in the physiologically relevant electrolyte of phosphate-buffered saline (PBS) with a response time of less than 5 s. The sensitivity is calculated as 86 μA mM-1 cm-2 from the linear region of the sensor response to the glucose concentration (20 μM to 0.27 mM). Also, Ni-MOF/CP has shown a good selective response toward glucose against uric acid, sucrose, fructose, and ascorbic acid. Additionally, the glucose sensing mechanism is investigated through work function changes of the sensing electrode using a scanning Kelvin probe. Real-time sample testing has revealed that the sensor preserves the sensitivity in human saliva too. In summary, we conclude that the Ni-MOF/CP extended gate electrode EGFET is an alternative device for salivary glucose detection toward the noninvasive diagnosis of diabetes mellitus that can identify hyperglycemic, normal, and hypoglycemic conditions. 

The rise of paper electronics has been accelerated due to the public push for sustainability. Electronic waste can potentially be avoided if certain materials in electronic components can be substituted for greener alternatives such as paper. Within this report, it is demonstrated that conductive polymers poly(3,4-ethylenedoxythiophene) (PEDOT), polypyrrole, and polythiophene, can be synthesized by screen printing combined with vapor phase polymerization on paper substrates and further incorporated into functional electronic components. High patterning resolution (100 µm) is achieved for all conductive polymers, with PEDOT showing impressive sheet resistance values. PEDOT is incorporated as conductive circuitry and as the active material in all-printed electrochromic displays. The conductive polymer circuits allow for functional light emitting diodes, while the electrochromic displays are comparable to commercial displays utilizing PEDOT on plastic substrates. 

Cellulose is the most abundant organic material on our planet which has a key role in our daily life (e.g., paper, packaging). In recent years, the need for replacing fossil-based materials has expanded the application of cellulose and cellulose derivatives including into electronics and sensing. The combination of nanostructures with cellulose nanofibers (CNFs) is expected to create new opportunities for the development of innovative electronic devices. In this paper, we report on a single-step process for the low temperature (<100 °C), environmentally friendly, and fully scalable CNF-templated highly dense growth of zinc oxide (ZnO) nanorods (NRs). More specifically, the effect of the degree of substitution of the CNF (enzymatic CNFs and carboxymethylated CNFs with two different substitution levels) on the ZnO growth and the application of the developed ZnO NRs/CNF nanocomposites in the development of UV sensors is reported herein. The results of this investigation show that the growth and nature of ZnO NRs are strongly dependent on the charge of the CNFs; high charge promotes nanorod growth whereas with low charge, ZnO isotropic microstructures are created that are not attached to the CNFs. Devices manufactured via screen printing/drop-casting of the ZnO NRs/CNF nanocomposites demonstrate a good photo-sensing response with a very stable UV-induced photocurrent of 25.84 µA. This also exhibits excellent long-term stability with fast ON/OFF switching performance under the irradiance of a UV lamp (15 W). 

Triboelectric nanogenerators (TENGs) are a new class of energy harvesting devices that have the potential to become a dominating technology for producing renewable energy. The versatility of their designs allows TENGs to harvest mechanical energy from sources like wind and water. Currently used renewable energy technologies have a restricted number of materials from which they can be constructed, such as metals, plastics, semiconductors, and rare-earth metals. These materials are all non-renewable in themselves as they require mining/drilling and are difficult to recycle at end of life. TENGs on the other hand can be built from a large repertoire of materials, including materials from bio-based sources. Here, a TENG constructed fully from wood-derived materials like lignin, cellulose, paper, and cardboard, thus making it 100% green, recyclable, and even biodegradable, is demonstrated. The device can produce a maximum voltage, current, and power of 232 V, 17 mA m–2, and 1.6 W m–2, respectively, which is enough to power electronic systems and charge 6.5 µF capacitors. Finally, the device is used in a smart package application as a self-powered impact sensor. The work shows the feasibility of producing renewable energy technologies that are sustainable both with respect to their energy sources and their material composition. © 2022 The Authors.