Real Time Analysis of Bioanalytes in Healthcare, Food, Zoology and Botany

Sensing Utilities of Cesium Lead Halide Perovskites and Composites: A Comprehensive Review

Recently, the utilization of metal halide perovskites in sensing and their application in environmental studies have reached a new height. Among the different metal halide perovskites, cesium lead halide perovskites (CsPbX3; X = Cl, Br, and I) and composites have attracted great interest in sensing applications owing to their exceptional optoelectronic properties. Most CsPbX3 nanostructures and composites possess great structural stability, luminescence, and electrical properties for developing distinct optical and photonic devices. When exposed to light, heat, and water, CsPbX3 and composites can display stable sensing utilities. Many CsPbX3 and composites have been reported as probes in the detection of diverse analytes, such as metal ions, anions, important chemical species, humidity, temperature, radiation photodetection, and so forth. So far, the sensing studies of metal halide perovskites covering all metallic and organic-inorganic perovskites have already been reviewed in many studies. Nevertheless, a detailed review of the sensing utilities of CsPbX3 and composites could be helpful for researchers who are looking for innovative designs using these nanomaterials. Herein, we deliver a thorough review of the sensing utilities of CsPbX3 and composites, in the quantitation of metal ions, anions, chemicals, explosives, bioanalytes, pesticides, fungicides, cellular imaging, volatile organic compounds (VOCs), toxic gases, humidity, temperature, radiation, and photodetection. Furthermore, this review also covers the synthetic pathways, design requirements, advantages, limitations, and future directions for this material.

Biomimetic Ion Channel Regulation for Temperature-Pressure Decoupled Tactile Perception

The perception of temperature and pressure of skin plays a vital role in joint movement, hand grasp, emotional expression, and self-protection of human. Among many biomimetic materials, ionic gels are uniquely suited to simulate the function of skin due to its ionic transport mechanism. However, both the temperature and pressure sensing are heavily dependent on the changes in ionic conductivity, making it impossible to decouple the temperature and pressure signals. Here, a pressure-insensitive and temperature-modulated ion channel is designed by synergistic strategies for gel skeleton's compact packing and ultra-thin structure, mimicking the function of the temperature ion channel in human skin. This ion-confined gel can completely suppress the pressure response of the temperature sensing layer. Furthermore, a temperature-pressure decoupled ionic sensor is fabricated and it is demonstrated that the ionic sensor can sense complex signals of temperature and pressure. This novel and effective approach has great potential to overcome one of the current barriers in developing ionic skin and extending its applications.

Metal–Oxide Nanowire Molecular Sensors and Their Promises

During the past two decades, one–dimensional (1D) metal–oxide nanowire (NW)-based molecular sensors have been witnessed as promising candidates to electrically detect volatile organic compounds (VOCs) due to their high surface to volume ratio, single crystallinity, and well-defined crystal orientations. Furthermore, these unique physical/chemical features allow the integrated sensor electronics to work with a long-term stability, ultra-low power consumption, and miniature device size, which promote the fast development of “trillion sensor electronics” for Internet of things (IoT) applications. This review gives a comprehensive overview of the recent studies and achievements in 1D metal–oxide nanowire synthesis, sensor device fabrication, sensing material functionalization, and sensing mechanisms. In addition, some critical issues that impede the practical application of the 1D metal–oxide nanowire-based sensor electronics, including selectivity, long-term stability, and low power consumption, will be highlighted. Finally, we give a prospective account of the remaining issues toward the laboratory-to-market transformation of the 1D nanostructure-based sensor electronics.

Sweat-Based Noninvasive Skin-Patchable Urea Biosensors with Photonic Interpenetrating Polymer Network Films Integrated into PDMS Chips

A wearable noninvasive biosensor for in situ urea detection and quantification was developed using a urease-immobilized photonic interpenetrating polymer network (IPN_urease) film. The photonic IPN film was intertwined with solid-state cholesteric liquid crystals (CLC_solid) and a poly(acrylic acid) (PAA) network on a flexible poly(ethylene terephthalate) substrate adhered to a poly(dimethylsiloxane) (PDMS) chip that was fabricated using an aluminum mold. The presence of urea in the chemical matrix of human sweat red-shifted the reflected color of the photonic IPN_urease film, and quantification was achieved by observing the wavelength at the photonic band gap (λ_PBG) with a limit of detection of 0.4 mM and a linear range of 0.9-50 mM. The color changes observed in the photonic IPN film were digitalized using the CIE 1931 xy coordinates on a cell phone image, thereby enabling fast, direct diagnosis via a downloadable app. This novel PDMS chip can be expanded for use with other biosensors.

Sensing Exposure Time to Oxygen by Applying a Percolation-Induced Principle

The determination of food freshness along manufacturer-to-consumer transportation lines is a challenging problem that calls for cheap, simple, reliable, and nontoxic sensors inside food packaging. We present a novel approach for oxygen sensing in which the exposure time to oxygen-rather than the oxygen concentration per se-is monitored. We developed a nontoxic hybrid composite-based sensor consisting of graphite powder (conductive filler), clay (viscosity control filler) and linseed oil (the matrix). Upon exposure to oxygen, the insulating linseed oil is oxidized, leading to polymerization and shrinkage of the matrix and hence to an increase in the concentration of the electrically conductive graphite powder up to percolation, which serves as an indicator of food spoilage. In the developed sensor, the exposure time to oxygen (days to weeks) is obtained by measuring the electrical conductivity though the sensor. The sensor functionality could be tuned by changing the oil viscosity, the aspect ratio of the conductive filler, and/or the concentration of the clay, thereby adapting the sensor to monitoring the quality of food products with different sensitivities to oxygen exposure time (e.g., fish vs grain).

Recent Developments of Flexible and Stretchable Electrochemical Biosensors

The skyrocketing popularity of health monitoring has spurred increasing interest in wearable electrochemical biosensors. Compared with the traditionally rigid and bulky electrochemical biosensors, flexible and stretchable devices render a unique capability to conform to the complex, hierarchically textured surfaces of the human body. With a recognition element (e.g., enzymes, antibodies, nucleic acids, ions) to selectively react with the target analyte, wearable electrochemical biosensors can convert the types and concentrations of chemical changes in the body into electrical signals for easy readout. Initial exploration of wearable electrochemical biosensors integrates electrodes on textile and flexible thin-film substrate materials. A stretchable property is needed for the thin-film device to form an intimate contact with the textured skin surface and to deform with various natural skin motions. Thus, stretchable materials and structures have been exploited to ensure the effective function of a wearable electrochemical biosensor. In this mini-review, we summarize the recent development of flexible and stretchable electrochemical biosensors, including their principles, representative application scenarios (e.g., saliva, tear, sweat, and interstitial fluid), and materials and structures. While great strides have been made in the wearable electrochemical biosensors, challenges still exist, which represents a small fraction of opportunities for the future development of this burgeoning field.

Near-Field Communication Sensors

Near-field communication is a new kind of low-cost wireless communication technology developed in recent years, which brings great convenience to daily life activities such as medical care, food quality detection, and commerce. The integration of near-field communication devices and sensors exhibits great potential for these real-world applications by endowing sensors with new features of powerless and wireless signal transferring and conferring near field communication device with sensing function. In this review, we summarize recent progress in near field communication sensors, including the development of materials and device design and their applications in wearable personal healthcare devices. The opportunities and challenges in near-field communication sensors are discussed in the end.

Tunable Adhesion for Bio-Integrated Devices

With the rapid development of bio-integrated devices and tissue adhesives, tunable adhesion to soft biological tissues started gaining momentum. Strong adhesion is desirable when used to efficiently transfer vital signals or as wound dressing and tissue repair, whereas weak adhesion is needed for easy removal, and it is also the essential step for enabling repeatable use. Both the physical and chemical properties (e.g., moisture level, surface roughness, compliance, and surface chemistry) vary drastically from the skin to internal organ surfaces. Therefore, it is important to strategically design the adhesive for specific applications. Inspired largely by the remarkable adhesion properties found in several animal species, effective strategies such as structural design and novel material synthesis were explored to yield adhesives to match or even outperform their natural counterparts. In this mini-review, we provide a brief overview of the recent development of tunable adhesives, with a focus on their applications toward bio-integrated devices and tissue adhesives.