Analysis of free chlorine in aqueous solution at very low concentration with lateral flow tests

Magnetic Particle Spectroscopy for Point-of-Care: A Review on Recent Advances

Since its first report in 2006, magnetic particle spectroscopy (MPS)-based biosensors have flourished over the past decade. Currently, MPS are used for a wide range of applications, such as disease diagnosis, foodborne pathogen detection, etc. In this work, different MPS platforms, such as dual-frequency and mono-frequency driving field designs, were reviewed. MPS combined with multi-functional magnetic nanoparticles (MNPs) have been extensively reported as a versatile platform for the detection of a long list of biomarkers. The surface-functionalized MNPs serve as nanoprobes that specifically bind and label target analytes from liquid samples. Herein, an analysis of the theories and mechanisms that underlie different MPS platforms, which enable the implementation of bioassays based on either volume or surface, was carried out. Furthermore, this review draws attention to some significant MPS platform applications in the biomedical and biological fields. In recent years, different kinds of MPS point-of-care (POC) devices have been reported independently by several groups in the world. Due to the high detection sensitivity, simple assay procedures and low cost per run, the MPS POC devices are expected to become more widespread in the future. In addition, the growth of telemedicine and remote monitoring has created a greater demand for POC devices, as patients are able to receive health assessments and obtain results from the comfort of their own homes. At the end of this review, we comment on the opportunities and challenges for POC devices as well as MPS devices regarding the intensely growing demand for rapid, affordable, high-sensitivity and user-friendly devices.

Magnetic nanoparticles and magnetic particle spectroscopy-based bioassays: a 15 year recap

Magnetic nanoparticles (MNPs) have unique physical and chemical properties, such as high surface area to volume ratio and size-related magnetism, which are completely different from their bulk materials. Benefiting from the facile synthesis and chemical modification strategies, MNPs have been widely studied for applications in nanomedicine. Herein, we firstly summarized the designs of MNPs from the perspectives of materials and physicochemical properties tailored for biomedical applications. Magnetic particle spectroscopy (MPS), first reported in 2006, has flourished as an independent platform for many biological and biomedical applications. It has been extensively reported as a versatile platform for a variety of bioassays along with the artificially designed MNPs, where the MNPs serve as magnetic nanoprobes to specifically probe target analytes from fluid samples. In this review, the mechanisms and theories of different MPS platforms realizing volumetric- and surface-based bioassays are discussed. Some representative works of MPS platforms for applications such as disease diagnosis, food safety and plant pathology monitoring, drug screening, thrombus maturity assessments are reviewed. At the end of this review, we commented on the rapid growth and booming of MPS-based bioassays in its first 15 years. We also prospected opportunities and challenges that portable MPS devices face in the rapidly growing demand for fast, inexpensive, and easy-to-use biometric techniques.

Experimental insights into anodic oxidation of hexafluoropropylene oxide dimer acid (GenX) on boron-doped diamond anodes

GenX is the trade name of the ammonium salt of hexafluoropropylene oxide dimer acid (HFPO-DA) and is used as a replacement for the banned perfluorooctanoic acid (PFOA). However, recent studies have found GenX to be more toxic than PFOA. This work deals with the electrochemical degradation of HFPO-DA using boron-doped diamond anodes. For the first time, an experimental study was conducted to investigate the influence of sulfate concentration and other operating parameters on HFPO-DA degradation. Results demonstrated that sulfate radicals were ineffective in HFPO-DA degradation due to steric hindrance by -CF₃ branch. Direct electron transfer was found as the rate-determining step. By comparing degradation of HFPO-DA with that of PFOA, it was observed that the steric hindrance by -CF₃ branch in HFPO-DA decreased the rate of electron transfer from the carboxyl head group even though its defluorination rate was faster. Conclusively, a degradation pathway is proposed in which HFPO-DA mineralizes to CO₂ and F- via formation of three intermediates.

Ten Years of Lateral Flow Immunoassay Technique Applications: Trends, Challenges and Future Perspectives

The Lateral Flow Immunoassay (LFIA) is by far one of the most successful analytical platforms to perform the on-site detection of target substances. LFIA can be considered as a sort of lab-in-a-hand and, together with other point-of-need tests, has represented a paradigm shift from sample-to-lab to lab-to-sample aiming to improve decision making and turnaround time. The features of LFIAs made them a very attractive tool in clinical diagnostic where they can improve patient care by enabling more prompt diagnosis and treatment decisions. The rapidity, simplicity, relative cost-effectiveness, and the possibility to be used by nonskilled personnel contributed to the wide acceptance of LFIAs. As a consequence, from the detection of molecules, organisms, and (bio)markers for clinical purposes, the LFIA application has been rapidly extended to other fields, including food and feed safety, veterinary medicine, environmental control, and many others. This review aims to provide readers with a 10-years overview of applications, outlining the trends for the main application fields and the relative compounded annual growth rates. Moreover, future perspectives and challenges are discussed.

Enhancing the Sensitivity of Lateral Flow Immunoassay by Magnetic Enrichment Using Multifunctional Nanocomposite Probes

For lateral flow immunoassay (LFIA), it is an important challenge to enhance the detection sensitivity to the same level as polymerase chain reaction or enzyme-linked immunosorbent assay to make LFIA pervasive in the field of on-site environmental analysis. We recently demonstrated that the LFIA sensitivity is dramatically enhanced by using Pt-nanoparticle-latex nanocomposite beads (Pt-P2VPs) as probes for the detection of the influenza A (H1N1) antigen compared with using conventional Au colloids as probes. Here, to further enhance the LFIA sensitivity using Pt-P2VPs, superparamagnetic iron oxide nanoparticles (SPIONs) were chemically conjugated to Pt-P2VPs (Pt-P2VP@SPION) to give them magnetic separation capability (enrichment and/or purification). To investigate the effect of magnetic enrichment on the LFIA sensitivity in a sandwich format, the C-reactive protein (CRP) was chosen as a model analyte and anti-CRP antibody (CRPAb)-conjugated Pt-P2VP@SPION (Pt-P2VP@SPION-CRPAb) beads were used as probes. The visual limit of detection (LOD) of LFIA was successfully lowered by increasing the magnetic enrichment factor φ. The minimum LOD under the present experimental conditions was 0.08 ng/mL for φ = 40, which is 26-fold lower than that of the standard Au-nanoparticle-based LFIA. In theory, the LOD can be unlimitedly decreased by just increasing φ. However, the times required for both the antigen-antibody binding reaction and magnetic separation dramatically increase with φ. We also propose solutions to overcome this drawback.

Comparison of the disinfecting effect of sodium hypochlorite aqueous solution and surfactant on hospital kitchen hygiene using adenosine triphosphate swab testing

The Japanese Ministry of Health requires large-scale cooking facilities to use sodium hypochlorite aqueous solution (HYP) on food preparation tools, equipment, and facilities to prevent secondary contamination. This study aimed to compare the disinfecting effect of HYP and surfactant using adenosine triphosphate (ATP) swab testing on large-scale equipment and facilities that could not be disassembled and disinfected in hospital kitchen. From May 2018 to July 2018, ATP swab tests were performed on the following six locations in the Shizuoka Cancer Centre Dietary Department Kitchen: cooking counter, mobile cooking counter, refrigerator handle, conveyor belt, tap handle, and sink. Six relative light unit (RLU) measurements were taken from each location. The log₁₀ values of the RLU measurements were evaluated by dividing the samples into two groups: the control group (surfactant followed by HYP swabbing) and the HYP group (HYP swabbing only). The results showed that the RLUs (log₁₀ values) in both the groups improved after disinfection (p<0.05), except for the RLUs (log₁₀ values) of the mobile cooking counter, tap handle, and sink in the control group after the HYP swab. The changes in the RLU (log₁₀ value) did not differ between the two groups for all locations of the kitchen. Hence, HYP swabbing of large-scale equipment and facilities provides the same level of disinfection as surfactants and can be as beneficial.

Functional paper-based materials for diagnostics

Functional papers are the subject of extensive research efforts and have already become an irreplaceable part of our modern society. Among other issues, they enable fast and inexpensive detection of a plethora of analytes and simplify laboratory work, for example in medical tests. This article focuses on the molecular and structural fundamentals of paper and the possibilities of functionalization, commercially available assays and their production, as well as on current and future challenges in research in this field.

Simplified formats of modern biosensors: 60 years of using immunochromatographic test systems in laboratory diagnostics

Immunochromatographic test systems known to foreign laboratory diagnostic experts as lateral flow immunoassay (LFIA) are simplified tape formats of modern biosensors. For 60 years, they have been widely used for the rapid detection of target molecules (ligands) in biosubstrates and the diagnosis of many diseases and conditions. The growing popularity of these test systems for providing medical care or diagnostics in developing countries, medical facilities, in emergency situations, as well as for individual home use by patients while monitoring their health are the main factors contributing to the continuous development and improvement of these methods, the emergence of a new generation of formats. The attractiveness and popularity of these fast, easy-to-use, inexpensive and portable diagnostic tools is associated primarily with their high analytical sensitivity and specificity, as well as the ease of interpretation of the results. These qualities have passed the test of time, and today LFIA test systems are fully consistent with the modern world concept of «point-of-care testing», finding wide application not only in medicine, but also in ecology, veterinary medicine, and agriculture. This review will highlight the modern principles of designing the most widely used formats of immunochromatographic test systems for clinical laboratory diagnostics, summarize the main advantages and disadvantages of the method, as well as current achievements and prospects of LFIA technology. Modern innovations aimed at improving the analytical characteristics of LFIA technology are interesting, promising and can bring additional benefits to immunochromatographic platforms that have gained popularity and attractiveness for six decades.

3,3',5,5'-tetramethylbenzidine as multi-colorimetric indicator of chlorine in water in line with health guideline values

Sanitizing solutions against bacterial and viral pathogens are of utmost importance in general and, in particular, in these times of pandemic due to Sars-Cov2. They frequently consist of chlorine-based solutions, or in the direct input of a certain amount of chlorine in water supply systems and swimming pools. Colorimetry is one of the techniques used to measure the crucial persistence of chlorine in water, including household chlorine test kits commonly based on colorimetric indicators. Here, we show a simple and cheap colorimetric method based on 3,3',5,5'-tetramethylbenzidine (TMB), commonly used as chromogenic reagent for enzyme-linked immunosorbent assays. TMB is converted by chlorine to a colored molecule through a pH-dependent multi-step oxidation process where the chromaticity of TMB is directly proportional to chlorine content. This molecule offers several advantages over other commonly used reagents in terms of safety, sensitivity, and, peculiarly, hue modulation, giving rise to the detection of chlorine in water with a multi-color change of the indicator solution (transparent/blue/green/yellow). Moreover, through the appropriate setting of reaction conditions, such coloration is finely tunable to cover the range of chlorine concentration recommended by international health agencies for treatment of drinking water and swimming pools and to test homemade solutions prepared by dilution of household bleach during health emergency events such as during the current pandemic. Graphical abstract.

Small-volume point-of-care analytical methods

Detecting clinically relevant diagnostic biomarkers, suitable for point-of-care detection, may facilitate rapid treatment and prevention of disease. However, medical diagnosis for which there are limited quantities of testable tissue or fluid, require point-of-care technologies with superior sensitivity and specificity. The purpose of this Editorial is to provide an overview of the Collection’s content, comprising original research into fluidics-based diagnostic platforms—specifically those made of paper or other low-cost materials, that can suitably operate with tiny sample volumes from mL to nL. In particular, we will focus on the clinical applications of such research, with potential uses in a number of fields including combating the COVID-19 pandemic for instance.

Six decades of lateral flow immunoassay: from determining metabolic markers to diagnosing COVID-19

Technologies based on lateral flow immunoassay (LFIA), known in some countries of the world as immunochromatographic tests, have been successfully used for the last six decades in diagnostics of many diseases and conditions as they allow rapid detection of molecular ligands in biosubstrates. The popularity of these diagnostic platforms is constantly increasing in healthcare facilities, particularly those facing limited budgets and time, as well as in household use for individual health monitoring. The advantages of these low-cost devices over modern laboratory-based analyzers come from their availability, opportunity of rapid detection, and ease of use. The attractiveness of these portable diagnostic tools is associated primarily with their high analytical sensitivity and specificity, as well as with the easy visual readout of results. These qualities explain the growing popularity of LFIA in developing countries, when applied at small hospitals, in emergency situations where screening and monitoring health condition is crucially important, and as well as for self-testing of patients. These tools have passed the test of time, and now LFIA test systems are fully consistent with the world's modern concept of ‘point-of-care testing’, finding a wide range of applications not only in human medicine, but also in ecology, veterinary medicine, and agriculture. The extensive opportunities provided by LFIA contribute to the continuous development and improvement of this technology and to the creation of new-generation formats. This review will highlight the modern principles of design of the most widely used formats of test-systems for clinical laboratory diagnostics, summarize the main advantages and disadvantages of the method, as well as the current achievements and prospects of the LFIA technology. The latest innovations are aimed at improving the analytical performance of LFIA platforms for the diagnosis of bacterial and viral infections, including COVID-19.