Optical sensors for determination of biogenic amines in food

This review presents the state-of-the-art of optical sensors for determination of biogenic amines (BAs) in food by publications covering about the last 10 years. Interest in the development of rapid and preferably on-site methods for quantification of BAs is based on their important role in implementation and regulation of various physiological processes. At the same time, BAs can develop in different kinds of food by fermentation processes or microbial activity or arise due to contamination, which induces toxicological risks and food poisoning and causes serious health issues. Therefore, various optical chemosensor systems have been devised that are easy to assemble and fast responding and low-cost analytical tools. If amenable to on-site analysis, they are an attractive alternative to existing instrumental analytical methods used for BA determination in food. Hence, also portable sensor systems or dipstick sensors are described based on various probes that typically enable signal readouts such as photometry, reflectometry, luminescence, surface-enhanced Raman spectroscopy, or ellipsometry. The quantification of BAs in real food samples and the design of the sensors are highlighted and the analytical figures of merit are compared. Future instrumental trends for BA sensing point to the use of cell phone-based fully automated optical evaluation and devices that could even comprise microfluidic micro total analysis systems

Comparison of Different Formats for Immunochromatographic Detection of Surfactant Nonylphenol

Immunochromatographic tests are of particular interest as tools for monitoring toxic environmental pollutants. In this regard, the aim of this study was to develop an immunochromatographic test system for the detection of surfactant nonylphenol in water. Two schemes of the assay were compared; they are characterized by detection limits of 1.1 and 0.4 μg/mL and recoveries of nonylphenol from spring water in the range of 78–113.7%

Tannic Acid-Capped Gold Nanoparticles as a Novel Nanozyme for Colorimetric Determination of Pb2+ Ions

In this study, tannic acid-modified gold nanoparticles were found to have superior nanozyme activity and catalyze the oxidation reaction of 3,3′,5,5′-tetramethylbenzidine in the presence of hydrogen peroxide. Enhancing the catalytic activity of the nanozyme by Pb2+ ions caused by selectively binding metal ions by the tannic acid-capped surface of gold nanoparticles makes them an ideal colorimetric probe for Pb2+. The parameters of the reaction, including pH, incubation time, and concentration of components, were optimized to reach maximal sensitivity of Pb2+ detection. The absorption change is directly proportional to the Pb2+ concentration and allows the determination of Pb2+ ions within 10 min. The colorimetric sensor is characterized by a wide linear range from 25 to 500 ng×mL−1 with a low limit of detection of 11.3 ng×mL−1. The highly sensitive and selective Pb2+ detection in tap, drinking, and spring water revealed the feasibility and applicability of the developed colorimetric sensor

Low-Tech Test for Mercury Detection: A New Option for Water Quality Assessment

Mercury pollution is a global environmental problem, especially in low-resource areas where artisanal iron mining is taking place and industrialization is on the rise. Therefore, there is a demand for simple methods for the determination of toxic metals at low. In this study, an on-field membrane lateral flow test system for sensitive and specific detection of Hg2+ in natural waters matrix is proposed. For this purpose, mercaptosuccinic acid (MSA) conjugated with protein-carrier (bovine serum albumin) was pre-impregnated in the test zone of the strip and used as a capping agent for mercury complexation. Quantitative evaluation of the analyte was provided by the use of gold nanoparticles stabilized with Tween-20 as a detecting agent. The sensing principle relies on the formation of Au–Hg nanoalloy during the migration of a solution containing Hg2+ along the strip, followed by capture in the test zone with the formation of a colored complex. Under optimum conditions, the proposed lateral flow test exhibited the linear correlation between color intensity in the test zone from the concentration of Hg2+ in the range of 0.04–25 ng/mL. The total analysis time was 11 min, without the need for the usage of additional instrumentation. The detection limit was estimated to be 0.13 ng/mL, which is 45 times lower than the WHO guidelines. The applicability of the proposed lateral flow test was confirmed by the analysis of natural waters, with the recoveries ranging from 70 to 120%. Due to the high affinity of Au to Hg and the use of a capping agent for mercury complexing, the developed system demonstrates high selectivity toward Hg2+. Compared to existing analytical methods, the proposed approach can be easily implemented and is characterized by economy and high analytical performance

Determination of Nonylphenol in a Highly Sensitive Chemiluminescent Immunoenzyme Assay of Natural Waters

A competitive chemiluminescent immunoenzyme assay (CL-EIA) technique is proposed for the sensitive determination of one of the environmentally significant toxicants of anthropogenic origin-nonylphenol—in natural waters. The chosen chemiluminescent detection is characterized by a higher sensitivity compared to the colorimetric. The limit of nonylphenol detection was 9 ng/mL compared to 55 ng/mL for colorimetric one in optimal conditions. The developed analysis can be used for two purposes; it is highly sensitive for the possibility of toxicological analysis and dilution of complex matrices with raw buffer solution, as well as for the analysis of water samples without pretreatment and dilution. The method has a working range from 28 to 1800 ng/mL. The degree of nonylphenol revealing in the spiked samples of river, spring, and waterfall water was 82–119%

Flexible Substrate of Cellulose Fiber/Structured Plasmonic Silver Nanoparticles Applied for Label-Free SERS Detection of Malathion

Surface-enhanced Raman scattering (SERS) is considered an efficient technique providing high sensitivity and fingerprint specificity for the detection of pesticide residues. Recent developments in SERS-based detection aim to create flexible plasmonic substrates that meet the requirements for non-destructive analysis of contaminants on curved surfaces by simply wrapping or wiping. Herein, we reported a flexible SERS substrate based on cellulose fiber (CF) modified with silver nanostructures (AgNS). A silver film was fabricated on the membrane surface with an in situ silver mirror reaction leading to the formation of a AgNS–CF substrate. Then, the substrate was decorated through in situ synthesis of raspberry-like silver nanostructures (rAgNS). The SERS performance of the prepared substrate was tested using 4-mercaptobenzoic acid (4-MBA) as a Raman probe and compared with that of the CF-based plasmonic substrates. The sensitivity of the rAgNS/AgNS–CF substrate was evaluated by determining the detection limit of 4-MBA and an analytical enhancement factor, which were 10 nM and ~107, respectively. Further, the proposed flexible rAgNS/AgNS–CF substrate was applied for SERS detection of malathion. The detection limit for malathion reached 0.15 mg/L, which meets the requirements about its maximum residue level in food. Thus, the characteristics of the rAgNS/AgNS–CF substrate demonstrate the potential of its application as a label-free and ready-to-use sensing platform for the SERS detection of trace hazardous substances

Mercaptosuccinic-Acid-Functionalized Gold Nanoparticles for Highly Sensitive Colorimetric Sensing of Fe(III) Ions

The development of reliable and highly sensitive methods for heavy metal detection is a critical task for protecting the environment and human health. In this study, a qualitative colorimetric sensor that used mercaptosuccinic-acid-functionalized gold nanoparticles (MSA-AuNPs) to detect trace amounts of Fe(III) ions was developed. MSA-AuNPs were prepared using a one-step reaction, where mercaptosuccinic acid (MSA) was used for both stabilization, which was provided by the presence of two carboxyl groups, and functionalization of the gold nanoparticle (AuNP) surface. The chelating properties of MSA in the presence of Fe(III) ions and the concentration-dependent aggregation of AuNPs showed the effectiveness of MSA-AuNPs as a sensing probe with the use of an absorbance ratio of A530/A650 as an analytical signal in the developed qualitative assay. Furthermore, the obvious Fe(III)-dependent change in the color of the MSA-AuNP solution from red to gray-blue made it possible to visually assess the metal content in a concentration above the detection limit with an assay time of less than 1 min. The detection limit that was achieved (23 ng/mL) using the proposed colorimetric sensor is more than 10 times lower than the maximum allowable concentration for drinking water defined by the World Health Organization (WHO). The MSA-AuNPs were successfully applied for Fe(III) determination in tap, spring, and drinking water, with a recovery range from 89.6 to 126%. Thus, the practicality of the MSA-AuNP-based sensor and its potential for detecting Fe(III) in real water samples were confirmed by the rapidity of testing and its high sensitivity and selectivity in the presence of competing metal ions

Development of Lateral Flow Test-System for the Immunoassay of Dibutyl Phthalate in Natural Waters

The use of a large amount of toxic synthetic materials leads to an increase in the pollution of environmental objects. Phthalates are compounds structurally related to esters of phthalic acid that are widely used in the manufacturing of synthetic packaging materials as plasticizers. Their danger is conditioned by leaching into the environment and penetrating into living organisms with negative consequences and effects on various organs and tissues. This work presents the first development of lateral flow immunoassay to detect dibutyl phthalate, one of the most common representatives of the phthalates group. To form a test zone, a hapten–protein conjugate was synthesized, and gold nanoparticles conjugated with antibodies to dibutyl phthalate were used as a detecting conjugate. The work includes the preparation of immunoreagents, selectivity investigation, and the study of the characteristics of the medium providing a reliable optical signal. Under the selected conditions for the analysis, the detection limit was 33.4 ng/mL, and the working range of the determined concentrations was from 42.4 to 1500 ng/mL. Time of the assay—15 min. The developed technique was successfully applied to detect dibutyl phthalate in natural waters with recovery rates from 75 to 115%

Structure- and Interaction-Based Design of Anti-SARS-CoV-2 Aptamers

Aptamer selection against novel infections is a complicated and time-consuming approach. Synergy can be achieved by using computational methods together with experimental procedures. This study aims to develop a reliable methodology for a rational aptamer in silico et vitro design. The new approach combines multiple steps: (1) Molecular design, based on screening in a DNA aptamer library and directed mutagenesis to fit the protein tertiary structure; (2) 3D molecular modeling of the target; (3) Molecular docking of an aptamer with the protein; (4) Molecular dynamics (MD) simulations of the complexes; (5) Quantum-mechanical (QM) evaluation of the interactions between aptamer and target with further analysis; (6) Experimental verification at each cycle for structure and binding affinity using small-angle X-ray scattering, cytometry, and fluorescence polarization. Using a new iterative design procedure, Interaction Based Drug Design (SIBDD), a highly specific aptamer to the receptor-binding domain of the SARS-CoV-2 spike protein, was developed and validated. The SIBDD approach enhances speed of the high-affinity aptamers development from scratch, using a target protein structure. The method could be used to improve existing aptamers for stronger binding. This approach brings to an advanced level the development of novel affinity probes, functional nucleic acids. It offers a blueprint for the straightforward design of targeting molecules for new pathogen agents and emerging variants.peerReviewe