Paper matrix based array for rapid and sensitive optical detection of mercury ions using silver enhancement

Microfluidic paper analytic device (μPAD) technology for food safety applications

Foodborne pathogens, food adulterants, allergens, and toxic chemicals in food can cause major health hazards to humans and animals. Stringent quality control measures at all stages of food processing are required to ensure food safety. There is, therefore, a global need for affordable, reliable, and rapid tests that can be conducted at different process steps and processing sites, spanning the range from the sourcing of food to the end-product acquired by the consumer. Current laboratory-based food quality control tests are well established, but many are not suitable for rapid on-site investigations and are costly. Microfluidic paper analytical devices (μPADs) are a fast-growing field in medical diagnostics that can fill these gaps. In this review, we describe the latest developments in the applications of microfluidic paper analytic device (μPAD) technology in the food safety sector. State-of-the-art μPAD designs and fabrication methods, microfluidic assay principles, and various types of μPAD devices with food-specific applications are discussed. We have identified the prominent research and development trends and future directions for maximizing the value of microfluidic technology in the food sector and have highlighted key areas for improvement. We conclude that the μPAD technology is promising in food safety applications by using novel materials and improved methods to enhance the sensitivity and specificity of the assays, with low cost.

Probe-impregnated monolithic polymer as a robust solid-state colorimetric chemosensor for selective sensing of Hg2+ in environmental water and cigarette samples

The current study developed a novel aqua-compatible and naked-eye portable solid-state opto-sensor for selective and sensitive detection of ultra-trace Hg²⁺ ions. The developed chemosensor was fabricated by the direct impregnation of a chromoionophoric probe composed of 2,3-bis((4-isopropylbenzylidene)amino)maleonitrile (PDPM) onto the surface of structurally tailored porous polymer monolithic framework. The template exhibited a highly porous network with greater surface area, which led to the effective anchoring of probe molecules onto the surface of the polymer template, thus serving as an efficient platform to constitute a regenerative solid-state chemosensor. The sensor rendered a superior color shift from dull white to dijon yellow after complexing with Hg²⁺. The surface, structural, and morphological aspects of the sensor were evaluated using FE-SEM, HR-TEM, EDAX, SAED, p-XRD, N₂ adsorption isotherm, and XPS. Rigorous optimization of the effects of different analytical parameters on the sensing performance of the PDPM sensor material was ensured. The monolithic sensor had an optimum sensing performance at pH 8.0, rapid signal response kinetics of 60s and a broad linear response range of 0.5-150.0 μg/L with a 0.22 μg/L detection limit. Furthermore, the sensor was also tolerant of foreign matrix constituents, thereby enabling it to be highly selective in detecting Hg²⁺. Sensor recovery was analyzed to be possible via Hg²⁺ desorption using 0.01 M EDTA without compromising its sensing performance. It had reutilization potential for up to eight regenerative cycles with excellent data reliability (recovery ≥99.4% and RSD ≤1.4%). The practicability of the fabricated sensor was investigated using various water and cigarette samples. Experimental data revealed that the developed chromoionophoric sensor was reusable, eco-friendly, low-cost, and possessed superior sensing capabilities, making it more feasible for on-site analysis of environmental samples. The designed sensor has the potential for further investigations and applications as a sensor kit for facilitating heavy metal detection in remote places.

A Comprehensive Review on Water Quality Monitoring Devices: Materials Advances, Current Status, and Future Perspective

Water quality monitoring has become more critical in recent years to ensure the availability of clean and safe water from natural aquifers and to understand the evolution of water contaminants across time and space. The conventional water monitoring techniques comprise of sample collection, preservation, preparation, tailed by laboratory testing and analysis with cumbersome wet chemical routes and expensive instrumentation. Despite the high accuracy of these methods, the high testing costs, laborious procedures, and maintenance associated with them don't make them lucrative for end end-users and field testing. As the participation of ultimate stakeholders, that is, common man for water quality and quantity can play a pivotal role in ensuring the sustainability of our aquifers, thus it is essential to develop and deploy portable and user-friendly technical systems for monitoring water sources in real-time or on-site. The present review emphasizes here on possible approaches including optical (absorbance, fluorescence, colorimetric, X-ray fluorescence, chemiluminescence), electrochemical (ASV, CSV, CV, EIS, and chronoamperometry), electrical, biological, and surface-sensing (SPR and SERS), as candidates for developing such platforms. The existing developments, their success, and bottlenecks are discussed in terms of various attributes of water to escalate the essentiality of water quality devices development meeting ASSURED criterion for societal usage. These platforms are also analyzed in terms of their market potential, advancements required from material science aspects, and possible integration with IoT solutions in alignment with Industry 4.0 for environmental application.

Paper-Based Analytical Devices for Colorimetric and Luminescent Detection of Mercury in Waters: An Overview

Lab-on-paper technologies, also known as paper-based analytical devices (PADs), have received increasing attention in the last years, and nowadays, their use has spread to virtually every application area, i.e., medical diagnostic, food safety, environmental monitoring, etc. Advantages inherent to on-field detection, which include avoiding sampling, sample preparation and conventional instrumentation in central labs, are undoubtedly driving many developments in this area. Heavy metals represent an important group of environmental pollutants that require strict controls due to the threat they pose to ecosystems and human health. In this overview, the development of PADs for Hg monitoring, which is considered the most toxic metal in the environment, is addressed. The main emphasis is placed on recognition elements (i.e., organic chromophores/fluorophores, plasmonic nanoparticles, inorganic quantum dots, carbon quantum dots, metal nanoclusters, etc.) employed to provide suitable selectivity and sensitivity. The performance of both microfluidic paper-based analytical devices and paper-based sensors using signal readout by colorimetry and luminescence will be discussed.

Progress in rapid optical assays for heavy metal ions based on the use of nanoparticles and receptor molecules

This review (with 230 refs.) covers recent progress in rapid optical assays for heavy metals (primarily lead and mercury as the most relevant) based on the use of nanoparticles and receptor molecules. An introduction surveys the importance, regulatory demands (such as maximum permissible concentrations) and potential and limitations of various existing methods. This is followed by a general discussion on the use of nanoparticles in optical assays of heavy metals (including properties, basic mechanisms of signal generation). The next sections cover methods for the functionalization of nanoparticles with (a) sulfur-containing compounds (used for modification of nanoparticles or added to the reaction medium), (b) nitrogen-containing compounds (such as amino acids, polypeptides, and heterocyclic molecules), and (c) oxygen-containing species (such as hydroxy and carbonyl compounds). This is continued by a specific description of specific assays based on the use of aptamers as receptors, on the use of deoxyribozymes as synthetic reaction catalysts, of G-quadruplex aptamers, of aptamers in logic gate-type of assays of linear (unstructured) aptamers ("hairpins"), and on the use of aptamers in lateral flow assays. A next section covers assays based on the employment of antibodies as receptors (used in the immunoassay development). The properties of various nanoparticles and their applicability in optical assays are also discussed in some detail. Final sections discuss the selectivity of assays, potential interferences by other cations, methods for their elimination, and also matrix effects and approaches for sample pretreatment. A concluding section discusses current challenges and future trends. Analysis based on enzyme inhibition assay is not treated here but enzyme-like action of some receptor molecules such as DNAzymes is discussed. Graphical abstract Schematic presentation of main principles of application of various nanoparticles with receptor molecules (S-, N-, O-containing, heterocyclic compounds, proteins, antibody, aptamers) for heavy metals ions detection. The included methods cover optical assays with description of mechanisms of interactions and signal generation.