Printed electronics are circuits that are additively manufactured using conductive pastes composed of micro-/nanoconductive metal particles. Silver-based compounds are the most widely used metals for such pastes due to their superior conductivity and oxidation stability. However, the high cost of silver (Ag) has demanded its replacement with more cost-effective and abundant metals such as copper (Cu). Despite its cost-effectiveness and abundance, Cu suffers from high oxidation tendency and sintering temperature that have limited its widespread utilization in printed electronics. In this work, we have developed a low-cost hybrid bimodal paste composed of Cu microparticles (1–5 μm) and Ag nanoparticles (20–30 nm) (CuMPs/AgNPs) via nondestructive photonic sintering. The concurrent melting of AgNPs and catalytic reduction of CuMPs allow the paste to be sintered at considerably low temperatures using an intense-pulsed light (IPL) source. The required light energy density for effective sintering of different mixing ratios of AgNPs and CuMPs was systematically measured using electrical, optical, and mechanical characterization techniques. These analyses revealed that a minimum of 16 wt % AgNPs in the bimodal CuMP/AgNP paste with an IPL irradiation energy of 10.6 J/cm2 and pulse duration of 5 ms achieved a minimum sheet resistance of 0.072 Ω/□ that results from localized melting of AgNPs between adjacent CuMPs. Furthermore, the CuMP/AgNP films with a minimum of 6 wt % AgNPs showed significantly improved oxidation stability characteristics even after 7 days of incubation in accelerated oxidation conditions [70 °C and 100% relative humidity (RH)]. As a proof of concept, we demonstrated an application of the developed paste (CuMPs-6 wt % AgNPs) by directly printing a wireless resonant moisture sensor onto the interior region of a cardboard package box, which is capable of performing in situ monitoring of the moisture ranging from 30 to 85% RH with an average linear sensitivity of −3.08 % RH/MHz.

In this work, a scalable and rapid process is developed for creating a low‐cost humidity sensor for wireless monitoring of moisture levels within packaged goods. The sensor comprises a moisture‐sensitive interdigitated capacitor connected to a planar spiral coil, forming an LC circuit whose resonant frequency is a function of environmental humidity. The sensor is fabricated on a commercially available metallized parchment paper through selective laser ablation of the laminated aluminum (Al) film on the parchment paper substrate. The laser ablation process provides a unique one‐step patterning of the conductive Al layer on the paper while simultaneously creating high surface area Al2O3 nanoparticles within the laser‐ablated regions. The intrinsic humidity‐responsive characteristics of the laser‐induced Al2O3 nanostructures provide the wireless sensor with a tenfold higher sensitivity to humidity than a similar LC resonant sensor prepared by conventional photolithography‐based processes on FR‐4 substrates. The frequency change of the sensor is observed to be a linear function within the range of 0−85% RH, providing an average sensitivity of −87 kHz RH−1 with good repeatability and stable performance. Furthermore, the employment of scalable laser fabrication processes using commercially available inexpensive materials renders these technologies viable for roll‐to‐roll manufacturing of low‐cost wireless sensors for smart packaging applications.

Originally developed for use in controlled laboratory settings, potentiometric ionselective electrode (ISE) sensors have recently been deployed for continuous, in situ measurement of analyte concentration in agricultural (e.g., nitrate), environmental (e.g., ocean acidification), industrial (e.g., wastewater), and health-care sectors (e.g., sweat sensors). However, due to uncontrolled temperature and lack of frequent calibration in these field applications, it has been difficult to achieve accuracy comparable to the laboratory setting. In this paper, we propose a novel temperature self-calibration method where the ISE sensors can serve as their own thermometer and therefore precisely measure the analyte concentration in the field condition by compensating for the temperature variations. We validate the method with controlled experiments using pH and nitrate ISEs, which use the Nernst principle for electrochemical sensing. We show that, using temperature self-calibration, pH and nitrate can be measured within 0.3% and 5% of the true concentration, respectively, under varying concentrations and temperature conditions. Moreover, we perform a field study to continuously monitor the nitrate concentration of an agricultural field over a period of 6 days. Our temperature self-calibration approach determines the nitrate concentration within 4% of the ground truth measured by laboratory-based high-precision nitrate sensors. Our approach is general and would allow battery-free temperature-corrected analyte measurement for all Nernst principle-based sensors being deployed as wearable or implantable sensors.

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Precision Agriculture (PA) is an integral component of the contemporary agricultural revolution that focuses on enhancing food productivity in proportion to the increasing global population while minimizing resource waste. While the recent advancements in PA, such as the integration of IoT (Internet of Things) sensors, have significantly improved the surveillance of field conditions to achieve high yields, the presence of batteries and electronic chips makes them expensive and non-biodegradable. To address these limitations, for the first time, we have developed a fully Degradable Intelligent Radio Transmitting Sensor (DIRTS) that allows remote sensing of subsoil volumetric water using drone-assisted wireless monitoring. The device consists of a simple miniaturized resonating antenna encapsulated in a biodegradable polymer material such that the resonant frequency of the device is dependent on the dielectric properties of the soil surrounding the encapsulated structure. The simple structure of DIRTS enables scalable additive manufacturing processes using cost-effective, biodegradable materials to fabricate them in a miniaturized size, thereby facilitating their automated distribution in the soil. As a proof-of-concept, we present the use of DIRTS in lab and field conditions where the sensors demonstrate the capability to detect volumetric water content within the range of 3.7–23.5% with a minimum sensitivity of 9.07 MHz/%. Remote sensing of DIRTS can be achieved from an elevation of 40 cm using drones to provide comparable performance to lab measurements. A systematic biodegradation study reveals that DIRTS can provide stable readings within the expected duration of 1 year with less than 4% change in sensitivity before signs of degradation. DIRTS provides a new steppingstone toward advancing precision agriculture while minimizing the environmental footprint.

Gamma radiation sterilization approach has been widely used for pharmaceutical packaging worldwide. Therefore, the development of an advanced dosimeter for monitoring the gamma radiation dosage during the sterilization process is...

a broad spectrum of applications due to their unique characteristics such as high mechanical flexibility, low cost, and scalable manufacturing. [1][2][3][4] However, many of the materials and processes used in PE devices often depend on nonbiodegradable polymer supporting substrates (such as silicone elastomers, polyethylene terephthalate, polyimide, etc.). [5][6][7][8][9] Considering the widespread implementation of PE, spanning from soft robots, human-machine interface, and flexible displays to advanced healthcare and virtual reality in the near future, the buildup of discarded electronic waste (e-waste) will cause adverse environmental effects. Recently, the United Nations has reported that by 2030 e-waste will grow up to 74 million metric tons on the planet, which will demand extensive landfill space for its appropriate disposal or recycling. [10] Therefore, researchers and scientists are highly inspired to find sustainable substitutes with the desired characteristics to address the concerns mentioned above.Recently, paper-based transient bioelectronics (PTB) composed of biodegradable materials have emerged as a new class of technology that can fully degrade to benign and environmentally safe by-products after they have served their primary function. [11][12][13][14] Despite the known bioresorbable characteristics of the paper substrates in PTB, the conductive traces and circuitry in these devices must be made from highly conductive and bioresorbable materials through Paper-based electronics are emerging as a new class of technology with broad areas of application. Despite several efforts to fabricate new types of flexible electronic devices by screen printing of conductive paste, many of them are often nonbiodegradable, toxic, and expensive, limiting their practical use in bioresorbable paper-based electronics. To address this need, a highly conductive and biodegradable bimodal conductive paste is developed using cost-effective zinc-based micro and nanoparticles with a facile low-temperature sintering process compatible with paper substrates. The two-step sintering process involves the removal of the insulating zinc oxide layer by spray coating acetic acid followed by a heat press sintering process to ensure the formation of highly packed and continuous metallic traces. The required conditions for the heat press sintering process are systematically studied using electrical, optical, and mechanical characterization techniques. The results of these investigations revealed an ultra-packed microstructure with high electrical conductivity (0.5 × 10 5 S m −1 ) and low oxide content that is obtained with a heat press sintering setting of 220 °C for 60 s. Finally, as a proof of concept, the conductive paste with an optimized sintering process is used to fabricate a wearable wireless heater for remote-controlled release of therapeutics. The controlled delivery of the system is validated in the practical and on-demand delivery of antibiotics for eradicating commonly found bacteria such as Staphylococcus aureus in derm...

Contamination of meat with pathogenic microorganisms can cause severe illnesses and food waste, which has significant negative impacts on both general health and the economy. In many cases, the expiration date is not a good indicator of meat freshness as there is a high risk of contamination during handling throughout the supply chain. Many biomarkers, including color, odor, pH, temperature, and volatile compounds, are used to determine spoilage. Among these, pH presents a simple and effective biomarker directly linked to the overgrowth of bacteria and degradation of the meat tissue. Low-cost methods for wireless pH monitoring are crucial in detecting spoilage on a large commercial scale. Existing technologies are often limited to short-range detection, with the use of batteries and different electronic components that increases both the manufacturing complexity and cost of the final device. To address these shortcomings, we have developed a cost-effective wireless pH sensor, which uses passive resonant frequency (RF) sensing, combined with a pH-responsive polymer that can be placed within packaged meat products and provide a remote assessment of the risk of microbial spoilage throughout the supply chain. The sensor tag consists of a sensing resonator coated with a pH-sensitive material and a passivated reference resonator operating in a differential frequency configuration. Upon exposure to elevated pH levels >6.8, the coating on the sensing resonator dissolves, which in turn results in a distinct change in the resonant frequency with respect to the reference resonator. Systematic theoretical and experimental results at different pH levels demonstrated that a 20% shift in resonant frequency demarcates the point for spoilage detection. As a proof of concept, the performance of the sensor in remotely detecting the risk of food spoilage was validated in packaged poultry over 10 days. The sensor fabrication process takes advantage of recent developments in the scalable manufacturing of flexible, low-cost devices, including selective laser etching of metalized plastic films and doctor-blade coating of stimuli-responsive polymer films. Furthermore, the biocompatibility of all the materials used in the sensor was confirmed with human intestinal cells (HCT-8 cells).