Dissolved oxygen amperometric sensor based on layer-by-layer assembly using host–guest supramolecular interactions

Gas nanosensors for health and safety applications in mining

The ever-increasing demand for accurate, miniaturized, and cost-effective gas sensing systems has eclipsed basic research across many disciplines. Along with the rapid progress in nanotechnology, the latest development in gas sensing technology is dominated by the incorporation of nanomaterials with different properties and structures. Such nanomaterials provide a variety of sensing interfaces operating on different principles ranging from chemiresistive and electrochemical to optical modules. Compared to thick film and bulk structures currently used for gas sensing, nanomaterials are advantageous in terms of surface-to-volume ratio, response time, and power consumption. However, designing nanostructured gas sensors for the marketplace requires understanding of key mechanisms in detecting certain gaseous analytes. Herein, we provide an overview of different sensing modules and nanomaterials under development for sensing critical gases in the mining industry, specifically for health and safety monitoring of mining workers. The interactions between target gas molecules and the sensing interface and strategies to tailor the gas sensing interfacial properties are highlighted throughout the review. Finally, challenges of existing nanomaterial-based sensing systems, directions for future studies, and conclusions are discussed.

The Challenges of O2 Detection in Biological Fluids: Classical Methods and Translation to Clinical Applications

Dissolved oxygen (DO) is deeply involved in preserving the life of cellular tissues and human beings due to its key role in cellular metabolism: its alterations may reflect important pathophysiological conditions. DO levels are measured to identify pathological conditions, explain pathophysiological mechanisms, and monitor the efficacy of therapeutic approaches. This is particularly relevant when the measurements are performed in vivo but also in contexts where a variety of biological and synthetic media are used, such as ex vivo organ perfusion. A reliable measurement of medium oxygenation ensures a high-quality process. It is crucial to provide a high-accuracy, real-time method for DO quantification, which could be robust towards different medium compositions and temperatures. In fact, biological fluids and synthetic clinical fluids represent a challenging environment where DO interacts with various compounds and can change continuously and dynamically, and further precaution is needed to obtain reliable results. This study aims to present and discuss the main oxygen detection and quantification methods, focusing on the technical needs for their translation to clinical practice. Firstly, we resumed all the main methodologies and advancements concerning dissolved oxygen determination. After identifying the main groups of all the available techniques for DO sensing based on their mechanisms and applicability, we focused on transferring the most promising approaches to a clinical in vivo/ex vivo setting.

Integration of Multiple Redox Centers into Porous Coordination Networks for Ratiometric Sensing of Dissolved Oxygen

The application of porphyrin metal-organic frameworks (MOFs) as a ratiometric electrochemical sensing platform is still unexplored. In this paper, we report a ratiometric electrochemical sensor by the integration of multiple redox centers into porphyrin MOFs for the detection of dissolved oxygen (DO). Specifically, the ferrocene (Fc) group was integrated into the nanosized PCN-222(Fe) (PCN = porous coordination networks) via acid-base reaction to synthesize the Fc@PCN-222(Fe) composite with two redox centers of the Fc group and Fe-porphyrin. The Fc group that is insensitive to DO serves as an internal reference, and the Fe-porphyrin in PCN-222(Fe) is a DO indicator. The ratios of the cathodic currents for the two redox centers exhibit a linear relationship with DO concentrations from 2.8 to 28.9 mg mL^-1 and a limit of detection of 0.3 mg mL^-1. In addition, the ratiometric electrochemical sensor has high selectivity and stability for DO sensing results from the Fc@PCN-222(Fe) composite. Because there are numerous redox centers, such as methylene blue and thionine, which can be integrated into MOFs, many MOF-based ratiometric electrochemical sensors can be simply developed for high-performance biosensing.

Modification of boron-doped diamond electrodes with gold-palladium nanoparticles for an oxygen sensor

Modification of boron-doped diamond (BDD) with gold-palladium nanoparticles (Au@PdNPs) was successfully performed. Prior to the modification, BDD was modified with allylamine to provide active sites for the attachment of nanoparticles, while the synthesis of Au@PdNPs was performed by chemical reduction of a palladium salt solution in a colloidal solution of gold nanoparticles. Characterization using TEM images showed that by controlling the palladium concentration, flower and core-shell shaped Au@PdNPs can be prepared. XPS studies confirmed that the nanoparticles with a flower shape could be attached better on the BDD surface. The Au@PdNPs-modified BDD (Au@PdNPs-BDD) electrodes were then examined for the oxygen reduction reaction in comparison with gold and palladium-based electrodes. One order higher current response was observed at Au@PdNPs-BDD compared to AuNPs-BDD, indicating the contribution of palladium in the oxygen reduction reaction. Good linearity with comparable limits of detection suggested that Au@PdNPs-BDD electrodes are promising for use as oxygen sensors. Furthermore, their application as BOD sensors was demonstrated.

Silver Nanoprism Enhanced Colorimetry for Precise Detection of Dissolved Oxygen

Dissolved oxygen (DO) content is an essential indicator for evaluating the quality of the water body and the main parameter for water quality monitoring. The development of high-precision DO detection methods is of great significance. This paper reports an integrated optofluidic device for the high precision measurement of dissolved oxygen based on the characteristics of silver nanoprisms. Metal nanoparticles, especially silver nanoprisms, are extremely sensitive to their surroundings. In glucose and glucose oxidase systems, dissolved oxygen will be transformed into H₂O₂, which affects the oxidation and erosion process of nanoprisms, then influences the optical properties of nanoparticles. By detecting the shift in the plasma resonance peak of the silver nanoparticles, the dissolved oxygen (DO) content can be determined accurately. Great reconfigurability is one of the most significant advantages of the optofluidic device. By simply adjusting the flow rate ratio between the silver nanoprisms flow and the water sample flow, real-time continuous adjustment of the detection ranges of DO from 0 to 16 mg/L can be realized dynamically. The detection limit of this device is as low as 0.11 µM (3.52 µg/L) for DO measurement. Thus, the present optofluidic system has a wide range of potential applications in fields of biomedical analyses and water sensing.

Review of Dissolved Oxygen Detection Technology: From Laboratory Analysis to Online Intelligent Detection

Dissolved oxygen is an important index to evaluate water quality, and its concentration is of great significance in industrial production, environmental monitoring, aquaculture, food production, and other fields. As its change is a continuous dynamic process, the dissolved oxygen concentration needs to be accurately measured in real time. In this paper, the principles, main applications, advantages, and disadvantages of iodometric titration, electrochemical detection, and optical detection, which are commonly used dissolved oxygen detection methods, are systematically analyzed and summarized. The detection mechanisms and materials of electrochemical and optical detection methods are examined and reviewed. Because external environmental factors readily cause interferences in dissolved oxygen detection, the traditional detection methods cannot adequately meet the accuracy, real-time, stability, and other measurement requirements; thus, it is urgent to use intelligent methods to make up for these deficiencies. This paper studies the application of intelligent technology in intelligent signal transfer processing, digital signal processing, and the real-time dynamic adaptive compensation and correction of dissolved oxygen sensors. The combined application of optical detection technology, new fluorescence-sensitive materials, and intelligent technology is the focus of future research on dissolved oxygen sensors.

Porphyrinoids for Chemical Sensor Applications

Porphyrins and related macrocycles have been intensively exploited as sensing materials in chemical sensors, since in these devices they mimic most of their biological functions, such as reversible binding, catalytic activation, and optical changes. Such a magnificent bouquet of properties allows applying porphyrin derivatives to different transducers, ranging from nanogravimetric to optical devices, also enabling the realization of multifunctional chemical sensors, in which multiple transduction mechanisms are applied to the same sensing layer. Potential applications are further expanded through sensor arrays, where cross-selective sensing layers can be applied for the analysis of complex chemical matrices. The possibility of finely tuning the macrocycle properties by synthetic modification of the different components of the porphyrin ring, such as peripheral substituents, molecular skeleton, coordinated metal, allows creating a vast library of porphyrinoid-based sensing layers. From among these, one can select optimal arrays for a particular application. This feature is particularly suitable for sensor array applications, where cross-selective receptors are required. This Review briefly describes chemical sensor principles. The main part of the Review is divided into two sections, describing the porphyrin-based devices devoted to the detection of gaseous or liquid samples, according to the corresponding transduction mechanism. Although most devices are based on porphyrin derivatives, seminal examples of the application of corroles or other porphyrin analogues are evidenced in dedicated sections.