The current application of nanotechnology in food and agriculture.

Disposable sensors are low-cost and easy-to-use sensing devices intended for short-term or rapid single-point measurements. The growing demand for fast, accessible, and reliable information in a vastly connected world makes disposable sensors increasingly important. The areas of application for such devices are numerous, ranging from pharmaceutical, agricultural, environmental, forensic, and food sciences to wearables and clinical diagnostics, especially in resource-limited settings. The capabilities of disposable sensors can extend beyond measuring traditional physical quantities (for example, temperature or pressure); they can provide critical chemical and biological information (chemo- and biosensors) that can be digitized and made available to users and centralized/decentralized facilities for data storage, remotely. These features could pave the way for new classes of low-cost systems for health, food, and environmental monitoring that can democratize sensing across the globe. Here, a brief insight into the materials and basics of sensors (methods of transduction, molecular recognition, and amplification) is provided followed by a comprehensive and critical overview of the disposable sensors currently used for medical diagnostics, food, and environmental analysis. Finally, views on how the field of disposable sensing devices will continue its evolution are discussed, including the future trends, challenges, and opportunities.

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Disposable Sensors in Diagnostics, Food, and Environmental Monitoring.

This review describes recent developments in the field of conductive nanomaterials and their application in 2D and 3D printed flexible electronics, with particular emphasis on inks based on metal nanoparticles and nanowires, carbon nanotubes, and graphene sheets. We present the basic properties of these nanomaterials, their stabilization in dispersions, formulation of conductive inks and formation of conductive patterns on flexible substrates (polymers, paper, textile) by using various printing technologies and post-printing processes. Applications of conductive nanomaterials for fabrication of various 2D and 3D electronic devices are also briefly discussed.

Conductive nanomaterials for 2D and 3D printed flexible electronics

Future sensing applications will include high-performance features, such as toxin detection, real-time monitoring of physiological events, advanced diagnostics, and connected feedback However, such multi-functional sensors require advancements in sensitivity, specificity, and throughput with the simultaneous delivery of multiple detection in a short time Recent advances in 3D printing and electronics have brought us closer to sensors with multiplex advantages, and additive manufacturing approaches offer a new scope for sensor fabrication To this end, we review the recent advances in 3D-printed cutting-edge sensors These achievements demonstrate the successful application of 3D-printing technology in sensor fabrication, and the selected studies deeply explore the potential for creating sensors with higher performance Further development of multi-process 3D printing is expected to expand future sensor utility and availability

The Boom in 3D-Printed Sensor Technology

We developed a new method to directly fabricate 3D multiaxial force sensor using fused deposition modeling (FDM) 3D printing of functionalized nanocomposite filaments. Here, 3D cubic cross shaped force sensor is suggested to measure the forces from three axes (x, y and z). The sensor has two components – a structural part and a sensing part – both of which are concurrently fabricated by 3D printing with different functional filaments. The structural part is printed with thermoplastic polyurethane (TPU) filament and the sensing part is printed with carbon nanotube (CNT)/TPU nanocomposite filament with a piezoresistivity on the surface of the structural part. The resistances of the sensing part are measured in three axial directions; Rx, Ry, and Rz and the force applied on each axis is measured by the resistance change. The 3D-printed multiaxial force sensor could detect the sub-millimeter scale deflection and its corresponding force on each axis. According to the sensing principle, when Fz = 4 N was applied, Rz was decreased by 2% while only 0.2% resistance change of Ry was induced. In addition, a simultaneous resistance measurement system was developed for a real-time force sensing in three axes. With its customizability, rapid manufacturing, and economic feasibility, this manufacturing approach allows direct fabrication of multiaxial sensors without additional assembly or integration processes.

3D printing of multiaxial force sensors using carbon nanotube (CNT)/thermoplastic polyurethane (TPU) filaments

Three-dimensional (3D) additive manufacturing techniques have been utilized to make 3D electrical components, such as resistors, capacitors, and inductors, as well as circuits and passive wireless sensors. Using the fused deposition modeling technology and a multiple-nozzle system with a printing resolution of 30 μm, 3D structures with both supporting and sacrificial structures are constructed. After removing the sacrificial materials, suspensions with silver particles are injected subsequently solidified to form metallic elements/interconnects. The prototype results show good characteristics of fabricated 3D microelectronics components, including an inductor–capacitor-resonant tank circuitry with a resonance frequency at 0.53 GHz. A 3D “smart cap” with an embedded inductor–capacitor tank as the wireless passive sensor was demonstrated to monitor the quality of liquid food (e.g., milk and juice) wirelessly. The result shows a 4.3% resonance frequency shift from milk stored in the room temperature environment for 36 h. This work establishes an innovative approach to construct arbitrary 3D systems with embedded electrical structures as integrated circuitry for various applications, including the demonstrated passive wireless sensors. A three-dimensional (3D) printing technology makes possible arbitrary-shaped, integrated microelectronic components and circuitry with existing products such as food containers. Customizing microsystems through layer-by-layer manufacturing techniques is an attractive proposition. However, the polymers used typically offer poor conductivity, making them unsuitable for microelectronic device applications. Liwei Lin and colleagues from the USA and Hsinchu address this problem by printing resistor, capacitor, and inductor devices composed of hollow polymer tubes. By injecting silver paste into the tubes, curing the metal, and removing the polymer support, they are able to generate intricate yet functional 3D circuits. The team demonstrates the potential of their approach by creating a “smart cap”—a wireless inductive sensor incorporated into a milk carton lid. The sensor detects shifts in liquid dielectric constant signals to warn consumers about potential food safety issues.

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3D-printed microelectronics for integrated circuitry and passive wireless sensors

/pdf/erratum-3d-printed-microelectronics-for-integrated-circuitry-4xb4hjw14k.pdf

Erratum: 3D-printed microelectronics for integrated circuitry and passive wireless sensors (Microsystems & Nanoengineering, (2015), 1, 15013, 10.1038/micronano.2015.13)

Sung Yueh Wu

Papers

3D-printed microelectronics for integrated circuitry and passive wireless sensors

Erratum: 3D-printed microelectronics for integrated circuitry and passive wireless sensors (Microsystems & Nanoengineering, (2015), 1, 15013, 10.1038/micronano.2015.13)