Wireless Tags with Hybrid Nanomaterials for Volatile Amine Detection

Geometric Transformation of Modified Multiwalled Carbon Nanotubes-Based Heterometallic Nanostructured Material: A Model for the Electrochemical Discrimination of Insecticides

Multifunctional carbon-based materials exhibit a large number of unprecedented active sites via an electron transfer process and act as a desired platform for exploring high-performance electroactive material. Herein, we exemplify the holistic design of a heterometallic nanostructured material (MWCNTs@KR-6/Mn/Sn/Pb) formed by the integration of metals (Mn2+, Sn2+, and Pb2+) and a dipodal ligand (KR-6) at the surface of multiwalled carbon nanotubes (MWCNTs). First, MWCNTs@KR-6 was readily synthesized via a noncovalent approach, which was further sequentially doped by Mn2+, Sn2+, and Pb2+ to give MWCNTs@KR-6/Mn/Sn/Pb. The designed material showed excellent electrochemical activity for the discrimination of insecticides belonging to structurally different classes. In contrast to that of the individual building components, both the stability and electrochemical activity of heterometallic nanostructured material were remarkably enhanced, resulting in a magnificent electrochemical performance of the developed material. Hence, the current work reports a comprehensive synthetic approach for MWCNTs@KR-6/Mn/Sn/Pb synthesis by synergizing unique properties of the heterometallic complex with MWCNTs. This work also offers a new insight into the design of multifunctional carbon-based materials for discrimination of different analytes on the basis of their redox potential.

Wireless Sensor for Meat Freshness Assessment Based on Radio Frequency Communication

Wireless communication technologies, particularly radio frequency (RF), have been widely explored for wearable electronics with secure and user-friendly information transmission. By exploiting the operational principle of chemically actuated resonant devices (CARDs) and the electrical response observed in chemiresistive materials, we propose a simple and hands-on alternative to design and manufacture RF tags that function as CARDs for wireless sensing of meat freshness. Specifically, the RF antennas were meticulously designed and fabricated by lithography onto a flexible substrate with conductive tape, and the RF signal was characterized in terms of amplitude and peak resonant frequency. Subsequently, a single-walled carbon nanotube (SWCNT)/MoS2/In2O3 chemiresistive composite was incorporated into the RF tag to convey it as CARDs. The RF signal was then utilized to establish a correlation between the sensor's electrical response and the RF attenuation signal (reflection coefficient) in the presence of volatile amines and seafood (shrimp) samples. The freshness of the seafood samples was systematically assessed throughout the storage time by utilizing the CARDs, thereby underscoring their effective potential for monitoring food quality. Specifically, the developed wireless tags provide cumulative amine exposure data within the food package, demonstrating a gradual decrease in radio frequency signals. This study illustrates the versatility of RF tags integrated with chemiresistors as a promising pathway toward scalable, affordable, and portable wireless chemical sensors.

In Situ Optical Detection of Amines at a Parts-per-Quadrillion Level by Severing the Through-Space Conjugated Supramolecular Domino

Conventional fluorophores suffer from low sensitivity and selectivity in amine detection due to the inherent limitations in their "one-to-one" stoichiometric sensing mechanism. Herein, we propose a "one-to-many" chain reaction-like sensing mechanism by creating a domino chain consisting of one fluorescent molecule (e.g., PTF1) and up to 40 nonemissive polymer chains (pPFPA) comprising over thousand repeating units (PFPA). PTF1 (the domino trigger) interacts with adjacent PFPA units (the following blocks) through polar-π interactions and initiates the domino effect, creating effective through-space conjugation along pPFPA chains and generating amplified yellow fluorescent signals through charge transfer between PTF1 and pPFPA. Amine exposure causes rapid dismantling of the fluorophore-pPFPA-based domino chain and significantly reduces the amplified emissions, thus providing an ultrasensitive method for detecting amines. Relying on the above merits, we achieve a limit of detection of 177 ppq (or 1.67 × 10-12 M) for triethylamine, which is nearly 4 orders lower than that of previous methods. Additionally, the distinct reactivity of pPFPA toward different amines allows for the discrimination of primary, secondary, and tertiary amines. This study presents a "domino effect" sensing mechanism that has not yet been reported and provides a general approach for chemical detection that is beyond the reach of conventional methods.

Wireless Detection of Trace Ammonia: A Chronic Kidney Disease Biomarker

Elevated levels of ammonia in breath can be linked to medical complications, such as chronic kidney disease (CKD), that disturb the urea balance in the body. However, early stage CKD is usually asymptomatic, and mass screening is hindered by high instrumentation and operation requirements and accessible and reliable detection methods for CKD biomarkers, such as trace ammonia in breath. Enabling methods would have significance in population screening for early stage CKD patients. We herein report a method to effectively immobilize transition metal selectors in close proximity to a single-walled carbon nanotube (SWCNT) surface using pentiptycene polymers containing metal-chelating backbone structures. The robust and modular nature of the pentiptycene metallopolymer/SWCNT complexes creates a platform that accelerates sensor discovery and optimization. Using these methods, we have identified sensitive, selective, and robust copper-based chemiresistive ammonia sensors that display low parts per billion detection limits. We have added these hybrid materials to the resonant radio frequency circuits of commercial near-field communication (NFC) tags to achieve robust wireless detection of ammonia at physiologically relevant levels. The integrated devices offer a noninvasive and cost-effective approach for early detection and monitoring of CKD.

Functionalized Multiwalled Carbon Nanotubes for Highly Stable Room Temperature and Humidity-Tolerant Triethylamine Sensing

Triethylamine (TEA) poses a significant threat to our health and is extremely difficult to detect at the parts-per-billion (ppb) level at room temperature. Carbon nanotubes (CNTs) are versatile materials used in chemiresistive vapor sensing. However, achieving high sensitivity and selectivity with a low detection limit remains a challenge for pristine CNTs, hindering their widespread commercial application. To address these issues, we propose functionalized multiwalled CNTs (MWCNTs) with carboxylic acid (COOH)-based sensing channels for ultrasensitive TEA detection under ambient conditions. Advanced structural analyses confirmed the necessary modification of MWCNTs after functionalization. The sensor exhibited excellent sensitivity to TEA in air, with a superior noise-free signal (10 ppb), an extremely low limit of detection (LOD ≈ 0.8 ppb), excellent repeatability, and long-term stability under ambient conditions. Moreover, the response values became more stable, demonstrating excellent humidity resistance (40-80% RH). Notably, the functionalized MWCNT sensor exhibited improved response and recovery kinetics (200 and 400 s) to 10 ppm of TEA compared to the pristine MWCNT sensor (400 and 1300 s), and the selectivity coefficient for TEA gas was improved by approximately three times against various interferants, including ammonia, formaldehyde, nitrogen dioxide, and carbon monoxide. The remarkable improvements in TEA detection were mainly associated with the large specific surface area, abundant active sites, adsorbed oxygen, and other defects. The sensing mechanism was thoroughly explained by using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and gas chromatography-mass spectrometry (GC-MS). This study provides a new platform for CNT-based chemiresistive sensors with high selectivity, low detection limits, and enhanced precision with universal potential for applications in food safety and environmental monitoring.

Rapid and visual evaluation the internal corruption of meat tissue by a designed near-infrared fluorescence probe with a broad pH response range

Rapid and visual evaluation the internal corruption of meat tissue is closely related to public health. The pH change caused by glycolysis and amino acid decomposition is an important indicator of meat freshness. Herein, we designed a pH-responsive NIR fluorescent probe (Probe-OH) based on protonation/deprotonation for monitoring the internal corruption of meat tissue. Probe-OH was synthesized by a stable hemicyanine skeleton with phenolic hydroxyl group, which exhibited excellent performances such as high selectivity, high sensitivity, fast response time (60 s), a broad pH-responsive range of 4.0-10.0, and superior spatio-temporal sampling ability. In addition, we conducted a paper chip platform to measure pH value in different meat samples (pork and chicken), which is convenient to evaluate pH value of meat by observing the color changes of paper strips. Furthermore, in combination with the NIR advantages of fluorescence imaging, Probe-OH was successfully applied to assess the freshness of pork and chicken breasts, and the structural changes of muscle tissue can be clearly observed under confocal microscope. The results of Z-axis scanning showed that Probe-OH could penetrate into the interior to monitor the internal corruption of meat tissue, the fluorescence intensity changes with scanning height in the meat tissue section, and reaches its maximum at 50 μm. To the best of our knowledge, there have been no reports of fluorescence probe being used to image the inside of meat tissue section so far. It is expected that we can provide a new rapid, sensitive, near-infrared fluorescence method for assessment of the freshness in the internal organization of meat.

Miniaturized wireless sensor enables real-time monitoring of food spoilage

Food spoilage results in food waste and food-borne diseases. Yet, standard laboratory tests to determine spoilage (mainly volatile biogenic amines) are not performed regularly by supply chain personnel or end customers. Here we developed a poly(styrene-co-maleic anhydride)-based, miniature (2 × 2 cm²) sensor for on-demand spoilage analysis via mobile phones. To demonstrate a real-life application, the wireless sensor was embedded into packaged chicken and beef; consecutive readings from meat samples using the sensor under various storage conditions enabled the monitoring of spoilage. While samples stored at room temperature showed an almost 700% change in sensor response on the third day, those stored in the freezer resulted in an insignificant change in sensor output. The proposed low-cost, miniature wireless sensor nodes can be integrated into packaged foods, helping consumers and suppliers detect spoilage of protein-rich foods on demand, and ultimately preventing food waste and food-borne diseases.

Highly sensitively detection of amine vapors released during shrimp spoilage by fluorescent molecules locked in covalent organic frameworks

The fluorescent sensors allow sensitive detection of amine vapors for assessing the safety and quality of seafood products. However, high diffusion resistance and insufficient recognition sites usually limit the sensitivity of the sensors. Here, we employed an emulsion-confined assembly strategy to uniform encapsulate fluorescent molecules perylene diimide (PDI) molecules into covalent organic frameworks (COFs) to achieve ultrasensitive detection of amine vapors. The detection mechanism is based on the photoinduced electron transfer from amine to the excited PDI. This method exhibits a broad linear detection range from 8 ppb to 800 ppm and the limit of detection reaches as low as 1.2 ppb. The real-time detection of the amine vapors produced during shrimp spoilage is successfully achieved with excellent performance. This provides a versatile method for the on-demand synthesis of functional materials with high fluorescence properties for the development of chemical sensors via encapsulating different fluorescent molecules into COFs.

Recent Progress in Amine Gas Sensors for Food Quality Monitoring: Novel Architectures for Sensing Materials and Systems

The increasing demand for food production has necessitated the development of sensitive and reliable methods of analysis, which allow for the optimization of storage and distribution while ensuring food safety. Methods to quantify and monitor volatile and biogenic amines are key to minimizing the waste of high-protein foods and to enable the safe consumption of fresh products. Novel materials and device designs have allowed the development of portable and reliable sensors that make use of different transduction methods for amine detection and food quality monitoring. Herein, we review the past decade's advances in volatile amine sensors for food quality monitoring. First, the role of volatile and biogenic amines as a food-quality index is presented. Moreover, a comprehensive overview of the distinct amine gas sensors is provided according to the transduction method, operation strategies, and distinct materials (e.g., metal oxide semiconductors, conjugated polymers, carbon nanotubes, graphene and its derivatives, transition metal dichalcogenides, metal organic frameworks, MXenes, quantum dots, and dyes, among others) employed in each case. These include chemoresistive, fluorometric, colorimetric, and microgravimetric sensors. Emphasis is also given to sensor arrays that record the food quality fingerprints and wireless devices that operate as radiofrequency identification (RFID) tags. Finally, challenges and future opportunities on the development of new amine sensors are presented aiming to encourage further research and technological development of reliable, integrated, and remotely accessible devices for food-quality monitoring.

Gas Sensors Based on Single-Wall Carbon Nanotubes

Single-wall carbon nanotubes (SWCNTs) have a high aspect ratio, large surface area, good stability and unique metallic or semiconducting electrical conductivity, they are therefore considered a promising candidate for the fabrication of flexible gas sensors that are expected to be used in the Internet of Things and various portable and wearable electronics. In this review, we first introduce the sensing mechanism of SWCNTs and the typical structure and key parameters of SWCNT-based gas sensors. We then summarize research progress on the design, fabrication, and performance of SWCNT-based gas sensors. Finally, the principles and possible approaches to further improving the performance of SWCNT-based gas sensors are discussed.

Facile monitoring of meat freshness with a self-constructed photosensitization colorimetric instrument

Total volatile basic nitrogen (TVB-N) produced from the decomposition of amino acids is an important indicator for meat freshness. Various pH-sensitive colorimetric films have been incorporated as intelligent packaging for meat freshness during food transportation. However, methods and instruments capable of on-site end-point detection of meat freshness are still needed for places that provide raw meat without packaging. Herein, based on amine-induced pH change that led to decreased color output of the 3,3',5,5'-tetramethylbenzidine (TMB)-based photosensitization colorimetric assay, a simple yet convenient instrument employing colorimetric indicator paper (CIP) was constructed for facile monitoring of meat freshness. Owing to the background color provided by the photosensitizer erythrosine (2',4',5',7'-tetraiodofluorescein, TIF), the color changed from blue to pink upon amine adsorption. A bespoke cellphone App was employed for image capture and color analysis of the CIP for freshness monitoring. The analytical results of amine (released from meat during storage) by the proposed method agreed well with those by a standard Conway dish method. In addition, the whole analytical process could be completed in about 5 min. The developed instrument may be potentially useful for on-site monitoring of meat freshness.

Smart choices: Mechanisms of intelligent food packaging

Intelligent food packaging is usually designed to monitor the state of the food itself and/or the environment around it, as well as the interactions between them, providing customers with information on food quality and/or safety through a variety of signals. They involve indicators (which inform by direct visual changes about specific properties related to food quality) and sensors (which detect specific analytes by using receptors, transducers, and signal processing electronics). A third type of intelligent packaging is known as data carriers, which are not typically used for information on food quality, but rather to track the movement of food along the food supply chain. In this graphical review, the basic mechanisms of intelligent food packaging systems are presented, as well as their main applications, with particular emphasis on those focused on food quality monitoring.