Fluorescence-Polarization-Based Assaying of Lysozyme with Chitooligosaccharide Tracers

Lysozyme is a well-known enzyme found in many biological fluids which plays an important role in the antibacterial protection of humans and animals. Lysozyme assays are used for the diagnosis of a number of diseases and utilized in immunohistochemistry, genetic and cellular engineering studies. The assaying methods are divided into two categories measuring either the concentration of lysozyme as a protein or its activity as an enzyme. While the first category of methods traditionally uses an enzyme-linked immunosorbent assay (ELISA), the methods for the determination of the enzymatic activity of lysozyme use either live bacteria, which is rather inconvenient, or natural peptidoglycans of high heterogeneity and variability, which leads to the low reproducibility of the assay results. In this work, we propose the use of a chemically synthesized substrate of a strictly defined structure to measure in a single experiment both the concentration of lysozyme as a protein and its enzymatic activity by means of the fluorescence polarization (FP) method. Chito-oligosaccharides of different chain lengths were fluorescently labeled and tested leading to the selection of the pentasaccharide as the optimal size tracer and the further optimization of the assay conditions for the accurate (detection limit 0.3 μM) and rapid (<30 min) determination of human lysozyme. The proposed protocol was applied to assay human lysozyme in tear samples and resulted in good correlation with the reference assay. The use of synthetic fluorescently labeled tracer, in contrast to natural peptidoglycan, in FP analysis allows for the development of a reproducible method for the determination of lysozyme activity.

DNA Probes for Cas12a-Based Assay with Fluorescence Anisotropy Enhanced Due to Anchors and Salts

CRISPR/Cas12a is a potent biosensing tool known for its high specificity in DNA analysis. Cas12a recognizes the target DNA and acquires nuclease activity toward single-stranded DNA (ssDNA) probes. We present a straightforward and versatile approach to transforming common Cas12a-cleavable DNA probes into enhancing tools for fluorescence anisotropy (FA) measurements. Our study involved investigating 13 ssDNA probes with linear and hairpin structures, each featuring fluorescein at one end and a rotation-slowing tool (anchor) at the other. All anchors induced FA changes compared to fluorescein, ranging from 24 to 110 mr. Significant FA increases (up to 180 mr) were obtained by adding divalent metal salts (Mg2+, Ca2+, Ba2+), which influenced the rigidity and compactness of the DNA probes. The specific Cas12a-based recognition of double-stranded DNA (dsDNA) fragments of the bacterial phytopathogen Erwinia amylovora allowed us to determine the optimal set (probe structure, anchor, concentration of divalent ion) for FA-based detection. The best sensitivity was obtained using a hairpin structure with dC10 in the loop and streptavidin located near the fluorescein at the stem in the presence of 100 mM Mg2+. The detection limit of the dsDNA target was equal to 0.8 pM, which was eight times more sensitive compared to the common fluorescence-based method. The enhancing set ensured detection of single cells of E. amylovora per reaction in an analysis based on CRISPR/Cas12a with recombinase polymerase amplification. Our approach is universal and easy to implement. Combining FA with Cas12a offers enhanced sensitivity and signal reliability and could be applied to different DNA and RNA analytes.

Rapid determination of domoic acid in seafood by fluorescence polarization immunoassay using a portable analyzer

Monitoring phycotoxin accumulation in marine products such as edible shellfish is a regulatory requirement in many countries. Therefore, a simple and rapid onsite quantification method is sought. Herein, we present a fluorescence polarization immunoassay (FPIA), a well-known one-step immunoassay, using a portable fluorescence polarization analyzer for domoic acid (DA), widely referred to as the primary toxin of amnesic shellfish poisoning (ASP). To establish FPIA for DA, the matrix effect of methanol, which is widely used to extract DA from shellfish, on FPIA was investigated. To validate this method, we performed a spike recovery test using oysters containing DA at a concentration equivalent to the regulatory limits of North America and the European Union (20 mg/kg). The recovery rate was found to be 79.4-114.7%, which is equivalent to that of the commercially available enzyme-linked immunosorbent assay (ELISA). We expect that this FPIA system will enable the quantitative onsite analysis of DA and significantly contribute to the safety of marine products.

Detection of Dibutyl Phthalate in Surface Water by Fluorescence Polarization Immunoassay

Dibutyl phthalate (DBP) is widely used as a plasticizer in the production of polymeric materials to give them flexibility, strength and extensibility. However, due to its negative impact on human health, in particular reproductive functions and fetal development, the content of DBP must be controlled in food and the environment. The present study aims to develop a sensitive, fast and simple fluorescence polarization immunoassay (FPIA) using monoclonal antibodies derived against DBP (MAb-DBP) for its detection in open waters. New conjugates of DBP with various fluorescein derivatives were obtained and characterized: 5-aminomethylfluorescein (AMF) and dichlorotriazinylaminofluorescein (DTAF). The advantages of using the DBP-AMF conjugate in the FPIA method are shown, the kinetics of binding of this chemical with antibodies are studied, the analysis is optimized, and the concentration of monoclonal antibodies is selected for sensitivity analysis-16 nM. The calibration dependence of the fluorescence polarization signal for the detection of DBP was obtained. The observed IC50 (DBP concentration at which a 50% decrease in the fluorescence polarization signal occurs, 40 ng/mL) and the limit of detection (LOD, 7.5 ng/mL) values were improved by a factor of 45 over the previously described FPIA using polyclonal antibodies. This technique was tested by the recovery method, and the high percentage of DBP discovery in water ranged from 85 to 110%. Using the developed method, real water samples from Lake Onega were tested, and a good correlation was shown between the results of the determination of DBP by the FPIA method and GC-MS. Thus, the FPIA method developed in this work can be used to determine DBP in open-water reservoirs.

Optical Sensors for Bacterial Detection

Analytical devices for bacterial detection are an integral part of modern laboratory medicine, as they permit the early diagnosis of diseases and their timely treatment. Therefore, special attention is directed to the development of and improvements in monitoring and diagnostic methods, including biosensor-based ones. A promising direction in the development of bacterial detection methods is optical sensor systems based on colorimetric and fluorescence techniques, the surface plasmon resonance, and the measurement of orientational effects. This review shows the detecting capabilities of these systems and the promise of electro-optical analysis for bacterial detection. It also discusses the advantages and disadvantages of optical sensor systems and the prospects for their further improvement.

BPA Endocrine Disruptor Detection at the Cutting Edge: FPIA and ELISA Immunoassays

BPA is a chemical commonly used in the production of polymer-based materials that can have detrimental effects on the thyroid gland and impact human reproductive health. Various expensive methods, such as liquid and gas chromatography, have been suggested for detecting BPA. The fluorescence polarization immunoassay (FPIA) is an inexpensive and efficient homogeneous mix-and-read method that allows for high-throughput screening. FPIA offers high specificity and sensitivity and can be carried out in a single phase within a timeframe of 20-30 min. In this study, new tracer molecules were designed that linked the fluorescein fluorophore with and without a spacer to the bisphenol A moiety. To assess the influence of the C6 spacer on the sensitivity of an assay based on the respective antibody, hapten-protein conjugates were synthesized and assessed for performance in an ELISA setup, and this resulted in a highly sensitive assay with a detection limit of 0.05 g/L. The lowest limit of detection was reached by employing the spacer derivate in the FPIA and was 1.0 μg/L, working range from 2 to 155 μg/L. The validation of the methods was conducted using actual samples compared to LC-MS/MS, which served as the reference method. The FPIA and ELISA both demonstrated satisfactory concordance.

A Sensitive Fluorescence Polarization Immunoassay for the Rapid Detection of Okadaic Acid in Environmental Waters

In this study, a homogeneous fluorescence polarization immunoassay (FPIA) for the detection of hazardous aquatic toxin okadaic acid (OA) contaminating environmental waters was for the first time developed. A conjugate of the analyte with a fluorophore based on a fluorescein derivative (tracer) was synthesized, and its interaction with specific anti-OA monoclonal antibodies (MAbs) was tested. A MAbs-tracer pair demonstrated highly affine immune binding (KD = 0.8 nM). Under optimal conditions, the limit of OA detection in the FPIA was 0.08 ng/mL (0.1 nM), and the working range of detectable concentrations was 0.4-72.5 ng/mL (0.5-90 nM). The developed FPIA was approbated for the determination of OA in real matrices: river water and seawater samples. No matrix effect of water was observed; therefore, no sample preparation was required before analysis. Due to this factor, the entire analytical procedure took less than 10 min. Using a compact portable fluorescence polarization analyzer enables the on-site testing of water samples. The developed analysis is very fast, easy to operate, and sensitive and can be extended to the determination of other aquatic toxins or low-molecular-weight water or food contaminants.

A Robust Homogeneous Fluorescence Polarization Immunoassay for Rapid Determination of Erythromycin in Milk

Erythromycin (ERY) is one of the most common macrolides applied in veterinary medicine to treat diseases or as a feed additive for animal growth promotion. Long-term irrational use of ERY could lead to residues in animal-derived food and the emergence of drug-resistant strains, posing potential threats to human health. In this study, a highly sensitive, specific, robust, and rapid fluorescence polarization immunoassay (FPIA) for the determination of ERY in milk has been described. Herein, to achieve high sensitivity, five tracers of ERY with different fluorescein structures were synthesized and paired with three monoclonal antibodies (mAbs). Under the optimized conditions, the combination of mAb 5B2 and tracer ERM-FITC achieved the lowest IC₅₀ value in the FPIA with 7.39 μg/L for ERM. The established FPIA was used to detect ERY in milk, revealing a limit of detection (LOD) of 14.08 μg/L with recoveries of 96.08-107.77% and coefficients of variations (CVs) of 3.41-10.97%. The total detection time of the developed FPIA was less than 5 min from the addition of samples to the result readout. All the above results showed that the proposed FPIA in this study was a rapid, accurate, and simple method for the screening of ERY in milk samples.

Fluorescence Polarization Immunoassay of Human Lactoferrin in Milk Using Small Single-Domain Antibodies

Due to its unique structure and properties, human breast milk lactoferrin (hLF) has many nutritional and health-promoting functions in infants, including protection against inflammation and bacterial infections. The lack of LF in breastmilk or formula can result in the weakening of the infant's immune system. Noncompetitive polarization fluorescence immunoassay (FPIA) is a promising method for hLF quantification in milk and dairy products, which does not require the separation of the bound and free protein and allows to avoid time-consuming sample preparation. The use of fluorescently labeled single-domain camelid antibodies (nanobodies) for protein recognition in FPIA makes it possible to quantify relatively large antigens, in particular, hLF. In this work, we used previously obtained fluorescein isothiocyanate (FITC)-conjugated anti-hLF5 and anti-hLF16 nanobodies, which selectively recognized two different human lactoferrin epitopes, but did not bind to goat lactoferrin. The kinetics of hLF interaction with the FITC-labeled nanobodies was studied. The dissociation constant (K_D) for the anti-LF5 and antiLF16 nanobodies was 3.2 ± 0.3 and 4.9 ± 0.4 nM, respectively, indicating the high-affinity binding of these nanobodies to hLF. We developed the FPIA protocol and determined the concentration of FITC-labeled anti-hLF5 and anti-hLF16 nanobodies that provided the optimal fluorescence signal and stable fluorescence polarization value. We also studied the dependence of fluorescence polarization on the hLF concentration in the noncompetitive FPIA with FITC-anti-hLF5 nanobody. The detection limit for hLF was 2.1 ± 0.2 µg/ml and the linear range for determining the hLF concentration was 3-10 µg/ml. FPIA is commonly used to assay low-molecular-weight substances; however, the use of fluorescently labeled nanobodies allows quantification of high-molecular-weight proteins. Here, we demonstrated that FPIA with fluorescently labeled nanobodies can be used for hLF quantification in milk.

Dual-Wavelength Fluorescence Polarization Immunoassay for Simultaneous Detection of Sulfonamides and Antibacterial Synergists in Milk

Combinations of sulfonamides (SAs) and antibacterial synergists (ASGs) are frequently used for treating infectious diseases and promoting growth for animals, which cause potential hazards to food safety and human health. To realize the simultaneous detection of SAs and ASGs in food, a homogeneous and high-throughput screening dual-wavelength fluorescence polarization immunoassay (DWFPIA) was developed. In this study, three SAs tracers and three ASGs tracers were synthesized by fluoresceins with different linkers and paired with their corresponding monoclonal antibodies (mAbs), respectively. To achieve a high sensitivity and broad specificity, the combination of tracers SADMPM-HDF with the longest linker paring mAb 10E6 for SAs and tracer HaptenA-DSCA paring mAb 9C9 for ASGs were chosen for the development of DWFPIA, achieving surprising IC₅₀ values for 23 SAs below 100 μg L^-1 and 5 ASGs below 50 μg L^-1. The accuracy of DWFPIA was applied in real milk samples by typical sulfamethazine (SMZ) and trimethoprim (TMP), with recoveries of 81.7-97.2% and 78.6-103.6%, and coefficient of variations (CVs) below 18.9%, which could be completed within 15 min, including sample pretreatment. We firstly developed a simultaneous screening DWFPIA, covering all of the SAs and ASGs used in clinic and providing a great application potential in food safety analysis.

Double Immunochromatographic Test System for Sensitive Detection of Phycotoxins Domoic Acid and Okadaic Acid in Seawater and Seafood

In this investigation, a double immunochromatographic analysis (ICA) of two relevant phycotoxins, domoic acid (DA) and okadaic acid (OA), was developed for the first time. The ICA was performed in the indirect competitive format using gold nanoparticles conjugated with anti-species antibodies. Under optimal conditions, the instrumental detection limits/cutoffs for simultaneous detection of DA and OA were 1.2/100 and 0.1/2.5 ng/mL, respectively. The time of the assay was 18 min. The ICA was applied to test seawater and a large panel of seafood, including mussels, tiger shrimps, octopuses, whelks, crabs, and scallops. The proposed simple sample preparation method for seafood takes only 20 min. For seawater, a dilution by buffer was implemented. The assay recoveries varied from 80.8% to 124.5%. The competitive potential of the proposed technique as a tool to control natural water and seafood samples is determined by its simplicity, rapidity, and sensitivity.

Influence of Endogenous Factors of Food Matrices on Avidin—Biotin Immunoassays for the Detection of Bacitracin and Colistin in Food

(Strept)avidin–biotin technology is frequently used in immunoassay systems to improve their analytical properties. It is known from clinical practice that many (strept)avidin–biotin-based tests provide false results when analyzing patient samples with a high content of endogenous biotin. No specific investigation has been carried out regarding possible interferences from avidin (AVI) and biotin (B₇) contained in food matrices in (strept)avidin–biotin-based immunoanalytical systems for food safety. Two kinds of competitive ELISAs for bacitracin (BT) and colistin (COL) determination in food matrices were developed based on conventional hapten–protein coating conjugates and biotinylated BT and COL bound to immobilized streptavidin (SAV). Coating SAV–B₇–BT and SAV–B₇–COL complexes-based ELISAs provided 2- and 15-times better sensitivity in BT and COL determination, corresponding to 0.6 and 0.3 ng/mL, respectively. Simultaneously with the determination of the main analytes, these kinds of tests were used as competitive assays for the assessment of AVI or B₇ content up to 10 and 1 ng/mL, respectively, in food matrices (egg, infant milk formulas enriched with B₇, chicken and beef liver). Matrix-free experiments with AVI/B₇-enriched solutions showed distortion of the standard curves, indicating that these ingredients interfere with the adequate quantification of analytes. Summarizing the experience of the present study, it is recommended to avoid immunoassays based on avidin–biotin interactions when analyzing biosamples containing these endogenous factors or enriched with B₇.

Registry of Acute Myocardial Infarction. REGION-MI - Russian Registry of Acute Myocardial Infarction

Aim      To study features of diagnosis and treatment of acute myocardial infarction (AMI) in Russian hospitals, results of the treatment, and early and late outcomes (6 and 12 months after AMI diagnosis); to evaluate the consistence of the treatment with clinical guidelines; and to evaluate patients' compliance with the treatment.Material and methods  The program was designed for 3 years, including 24 months for recruitment of patients to the study. The study will include 10, 000 patients hospitalized with a confirmed diagnosis (I21 according to ICD-10) of ST segment elevation acute myocardial infarction (MI) (STEMI) or non-ST segment elevation MI (NSTEMI) based on criteria of the European Society of Cardiology Guidelines on Forth Universal Definition of Myocardial Infarction (2018). The follow-up period was divided into three stages: observation during the stay in the hospital and at 6 and 12 months following inclusion into the registry. The primary endpoint included cardiac death, nonfatal MI during the hospitalization and after one-year follow-up. Secondary endpoints were 6-months and one-year incidence of repeated MI, heart failure, ischemic stroke, clinically significant hemorrhage, unscheduled revascularization after discharge from the hospital, and the proportion of patients who continue on statins, antiplatelet drugs, and drugs of other groups for 6 months and 1 year.Results The inclusion of patients into the registry started in 2020 and will continue for 24 months. By the time of the article publication (June, 2021), more than 2,000 patients will be included.Conclusion      REGION-MI (Russian rEGIstry Of acute myocardial iNfarction) is a multicenter, retrospective and prospective observational cohort study that excludes any interference with the clinical practice. Results of the registry will help to analyze a real picture of medical care provided to patients with myocardial infarction and to schedule ways to improve the situation.

Fluorescence polarization immunoassay for rapid determination of dehydroepiandrosterone in human urine

In this paper, five fluorescein-labeled dehydroepiandrosterone (DHEA) derivatives (tracers) with different chain lengths between the fluorescein and hapten were synthesized and featured so as to establish a fluorescence polarization immunoassay (FPIA) for DHEA detection in human urine samples with previously prepared polyclonal antibody against DHEA. The outcomes of the structure of tracer on FPIA sensitivity were investigated. Under the optimal condition, the fluorescence polarization value (FP) decreases linearly in DHEA concentration, ranging from 1.6 to 243.3 ng mL^-1, with the limit of detection of 1.1 ng mL^-1 and IC₅₀ value of 25.1 ng mL^-1. Moreover, the developed FPIA was time-saving as it could complete the detection within 3 min. FPIA and commercial enzyme-linked immunosorbent assay kit were both applied to analyze the spiked human urine samples with DHEA. Excellent recoveries (92.1-108.0%) and satisfactory correlation coefficient (R² = 0.98) were acquired with the two methods, indicating that the developed FPIA was a fast and efficient screening immunoassay with accuracy and sensitivity for DHEA detection in human urine samples. Graphical abstract.

Competitive and noncompetitive fluorescence polarization immunoassays for the detection of benzothiostrobin using FITC-labeled dendrimer-like peptides

Peptides obtained from phage display libraries are valuable reagents for small-molecule immunoassays. However, their application in fluorescence polarization immunoassays (FPIAs) is limited by phage particles. Here, monomer, dendrimer-like dimer, tetramer peptidomimetic and anti-immunocomplex tracers were designed and synthesized using lysine as special scaffolds and spacers to develop competitive and noncompetitive FPIAs for benzothiostrobin. The affinity between tracers and monoclonal antibodies or immunocomplexes increased with the tracer valence. A higher signal-to-noise ratio and sensitivity could be generated in the FPIAs based on tetramer tracers. The sensitivities of competitive (50% inhibitory concentration) and noncompetitive (50% saturation concentration) FPIAs were 19.71 ± 4.65 and 40.43 ± 2.73 ng mL^-1, respectively. The spiked recoveries were 78.3%-105.2% with relative standard deviations (RSDs) of 0.7%-15.4% for the competitive FPIA, while 78.7%-115.3% with RSDs of 0.7%-12.5% for the noncompetitive FPIA. The amounts of benzothiostrobin in rice detected by the FPIAs were consistent with those detected by high performance liquid chromatography.

Enhanced performance of a surface plasmon resonance-based immunosensor for the detection of glycocholic acid

The concentration of glycocholic acid (GCA) in urine and blood is an important biomarker for liver cancer. Monitoring of GCA depends to a large extent on the availability of appropriate analytical techniques. In this work, based on the immobilization of GCA-OVA onto the sensor chip surface, a label-free competitive inhibition immunoassay for the determination of GCA with the surface plasmon resonance (SPR) technique was developed. The proposed SPR immunosensor is simple to prepare, recyclable and exhibits excellent sensitivity to GCA (a linear range of 13.3-119.4 ng mL^-1 and a limit of detection (LOD) of 2.5 ng mL^-1), which was 14 times lower than that of the traditional immunoassay. Excellent recoveries and correlation between these two methods were observed (R² = 0.995). Hence, it can be proved that the SPR immunosensor could be used to achieve rapid and sensitive quantitative detection of GCA in real urine samples and meet clinical needs.

A copper nanoparticle-based electrochemical immunosensor for carbaryl detection

A hapten-protein conjugate with copper nanoparticles (Hap-Car-BSA@CuNPs) was first synthesized in the present work for the determination of carbaryl. The copper nanoparticles (CuNPs) of the conjugate were used as electrochemical labels in the direct solid-phase competitive determination of carbaryl residues in flour from different crops. The signal was read by linear sweep anodic stripping voltammetry (LSASV) of copper (through the electrochemical stripping of accumulated elemental copper) on a gold-graphite electrode (GGE). To form a recognition receptor layer of monoclonal antibodies against the carbaryl on the surface of the GGE, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and 1-hydroxy-2,5-pyrrolidinedione (NHS) were used as the best covalent cross-linkers. The concentrations of the antibodies and the Hap-Car-BSA@CuNPs conjugate were optimized for carbaryl detection by the electrochemical immunosensor. The electrochemical immunosensor can be used for highly sensitive determination of carbaryl residues in flour samples in the concentration range 0.8-32.3 μg·kg^-1, with a limit of detection 0.08 μg·kg^-1. The present work paves the path for a novel method for monitoring carbaryl in other food products, drinks, and soil samples.

Fluorescence polarization immunoassay for the determination of diclofenac in wastewater

Pharmacologically active compounds are often detected in wastewater and surface waters. The nonsteroidal anti-inflammatory drug diclofenac (DCF) was included in the European watch list of substances that requires its environmental monitoring in the member states. DCF may harmfully influence the ecosystem already at concentrations ≤ 1 μg L-1. The fast and easy quantification of DCF is becoming a subject of global importance. Fluorescence polarization immunoassay (FPIA) is a homogeneous mix-and-read method which does not require the immobilization of reagents. FPIA can be performed in one phase within 20-30 min, making it possible to analyse wastewater without any complicated pre-treatment. In this study, new tracer molecules with different structures, linking fluorophores to derivatives of the analyte, were synthesized, three homologous tracers based on DCF, two including a C6 spacer, and one heterologous tracer derived from 5-hydroxy-DCF. The tracer molecules were thoroughly assessed for performance. Regarding sensitivity of the FPIA, the lowest limit of detection reached was 2.0 μg L-1 with a working range up to 870 μg L-1. The method was validated for real wastewater samples against LC-MS/MS as reference method with good agreement of both methods. Graphical abstract.

Lateral Flow Immunosensor for Ferritin Based on Dual Signal-Amplified Strategy by Rhodium Nanoparticles

Lateral flow immunoassay (LFIA) is one of the most widely used tools for analysis and field measurement and has the advantages of high efficiency, simple operation, portability, and low cost. Therefore, in this study, we designed a proof-of-concept of LFIA based on rhodium nanoparticles and investigated its improvement by further introducing the tetramethyl benzidine and H₂O₂ mixture as the substrate to trigger the color reaction. The proposed methods were qualitative research by the naked eye and quantitative measurement by a smartphone and software. Under the optimal condition, the detection of ferritin was successfully established with the limit of detection of 0.3 ng/mL. The lowest visually detectable amount was 0.05 ng/mL. To verify the performance of the RhNPs-LFIA, three spiked serum samples were tested, and the recovery rate increased from 88.9 to 129.9%, revealing that the proposed methods were applicable and practically reliable for testing serum samples. The developed RhNP-based LFIA is highly sensitive and convenient, which provides a promising technology for accurate, rapid, high sensitivity, and high screening detection of ferritin in clinical diagnosis.

Fluorescence Polarization-Based Bioassays: New Horizons

Fluorescence polarization holds considerable promise for bioanalytical systems because it allows the detection of selective interactions in real time and a choice of fluorophores, the detection of which the biosample matrix does not influence; thus, their choice simplifies and accelerates the preparation of samples. For decades, these possibilities were successfully applied in fluorescence polarization immunoassays based on differences in the polarization of fluorophore emissions excited by plane-polarized light, whether in a free state or as part of an immune complex. However, the results of recent studies demonstrate the efficacy of fluorescence polarization as a detected signal in many bioanalytical methods. This review summarizes and comparatively characterizes these developments. It considers the integration of fluorescence polarization with the use of alternative receptor molecules and various fluorophores; different schemes for the formation of detectable complexes and the amplification of the signals generated by them. New techniques for the detection of metal ions, nucleic acids, and enzymatic reactions based on fluorescence polarization are also considered.

Development of Fluorescence Polarization Immunoassay for Imidacloprid in Environmental and Agricultural Samples

A fluorescence polarization immunoassay (FPIA) for the determination of imidacloprid (IMI) was developed with advantages of simple operation and short assay time. The haptens of IMI, acetamiprid (ACE), and thiamethoxam (THI) were conjugated with fluorescein isothiocyanate ethylenediamine (EDF) and 4'-Aminomethyl fluorescein (AMF), respectively, to prepare six fluorescence tracers. The conjugation of IMI hapten and EDF (IMI-EDF) was selected to develop the FPIA due to the largest fluorescent polarization value increase in the presence of anti-IMI monoclonal antibody. Under the optimum condition, the limit of detection, 50% inhibition concentration and detection range of the FPIA were 1.7, 4.8, and 1.7-16.3 μg/L, respectively. The cross-reactivities (CRs) with the analogs of IMI were negligible except for imidaclothiz with CR of 79.13%. The average recovery of spiked paddy water, corn and cucumber samples were 82.4-118.5% with the RSDs of 7.0-15.9%, which indicated the FPIA had good accuracy. Thus, the developed FPIA was a potential tool for the rapid and accurate determination of IMI in agricultural and environmental samples.

Immunochemical approaches for detection of aflatoxin B1 in herbal medicines

INTRODUCTION

Aflatoxin B1 (AFB1) is a toxic low-molecular-weight secondary metabolite of Aspergillus flavus and A. parasiticus. AFB1 was classified as a Group I carcinogen by the World Health Organisation for Research on Cancer in 1993. AFB1 is an unavoidable natural contaminant of some herbal medicine, able to cause serious health issues for humans consuming the related medicine.

OBJECTIVE

Therefore, this study aimed to develop an efficient fluorescence polarisation immunoassay (FPIA) and a rapid, low-cost, and easy-to-use membrane-based flow-through immunoassay (MBA) for determination of AFB1 in herbal medicine Origanum vulgare L., Rubus idaeus L., Urtica dioica L. and Sorbus aucuparia L.

RESULTS

A cut-off level of the developed MBA was 0.8 ppb. Validation of the developed test was performed with blank and spiked samples. Using three naturally contaminated or three artificially spiked samples. The FPIA showed a linear working range of 8.6 to 64 ppb, and a half maximal inhibitory concentration (IC₅₀ ) of 24 ppb.

CONCLUSION

The results were in good correlation with the enzymelinked immunosorbent assay (ELISA) results (the IC₅₀ 0.1 ppb). Both the sample preparation and analysis are simple, cost-effective and easy to perform on-site in non-laboratory environments. Liquid chromatography with tandem mass spectrometry (LC-MS/MS) was used as a confirmatory technique.

Development of a latex particles-based lateral flow immunoassay for group determination of macrolide antibiotics in breast milk

A lateral flow immunoassay (LFIA) using latex particles labeled with antibody to BSA-clarithromycin (CLA) was developed for the rapid simultaneous group determination of six macrolide antibiotics. Optimization of antigen spotting on the membrane and latex probe loading allowed improving visual detectability (vLOD) 100 times, which was 1, 1, 10, 10, 50, and 1000 ng/mL for CLA, roxithromycin, erythromycin, dirithromycin, azithromycin, and oleandomycin in buffer, respectively. The calculated limits of instrumental detection (cLOD) were respectively 0.12, 0.15, 1.4, 2.1, 2.4, and 3.3 ng/mL. To avoid a strong influence of breast milk of a very diverse and variable composition, a sample pretreatment is proposed. The six macrolides mentioned can be visually detected in breast milk after 20 min pretreatment at concentrations of 10-1000 ng/mL or instrumentally with cLOD of 4.0, 2.5, 30, 42, 42 and 180 ng/mL. The recovery rate from the spiked samples carried out using a strip scanner device ranged from 71 % to 110 %, and precision expressed as relative standard deviation was between 3-14 %. The described rapid on-site diagnostic assay format can be useful for monitoring the content of antibiotics in breast milk during macrolide treatment to ensure safe breastfeeding of infants.

Neuroprotective and Antioxidant Activity of Arachidonoyl Choline, Its Bis-Quaternized Analogues and Other Acylcholines

The antioxidant activity and protective effect in the toxicity model of H₂O₂ were studied for arachidonic (AA-CHOL), docosahexaenoic (DHA-CHOL), linoleic (Ln-CHOL), and oleic (Ol-CHOL) fatty acids, as well as arachidonoyl dicholine (AA-diCHOL) and O-arachidonoyl bistetramethylaminoisopropanol (ABTAP). AA-CHOL, DHA-CHOL and Ln-CHOL provided a 20% increase in cell survival. AA-CHOL, AA-diCHOL, Ol-CHOL, and ABTAP had a radical-scavenging effect in the ABTS test, approximately equal to the activity of a standard radical scavenger Trolox.

[Immunochromatographic analysis of determination of narcotic substances using test systems containing gold nanoparticles, on the example of morphine and amphetamine]

Currently, there is a constant expansion of the range of narcotic substances that differ from each other by a small structural fragment. The option of determining narcotic substances using test panels is widespread due to its rapidity and high specificity through the use of immunochemical reactions. The purpose of the study was to optimize the determination of morphine and amphetamine in bioobjects (synthetic and natural urine) using immunochromatographic analysis with new test panels and to select the optimal conditions for mass analysis. Test panels were used to detect the presence of amphetamine and morphine. For color recording of the results of analysis, colloidal gold nanoparticles were used. The principle of operation of these test panels is described. The sensitivity of the test panels is such that it is possible to avoid false-positive results. It was found that with the help of test panels it is possible to determine narcotic substances in a concentration lower than stated in the instructions (300 ng/ml). The actual detection limit for amphetamine was 75 ng/ml and morphine 100 ng/ml. The analytical characteristics of the developed metho-dology were determined: detection limit, precision, truth and specificity. The specificity was proved by conducting ICA to detect the presence of cross-reactions of test systems to amphetamine and morphine using structural analogues - adrenaline 1000 and codeine 300, respectively. The study did not receive false positive results for these molecules using the proposed test panels. Immunochromatographic test systems are optimal for drug detection, especially when conducting mass studies.

Specific and Generic Immunorecognition of Glycopeptide Antibiotics Promoted by Unique and Multiple Orientations of Hapten

Conjugation chemistry does not always provide adequate spatial orientation of hapten in immunogens for the best presentation of generic or individual epitopes. In the present study, the influence of unique and multiple orientations of immunizing hapten on the immune response repertoire was compared to select generic recognition system. The glycopeptides, teicoplanin (TPL) and ristomycin (RSM), were conjugated to BSA to produce immunogens with unique and multiple orientations of haptens. Polyclonal antibodies generated against TPL conjugated through a single site were of uniform specificity and demonstrated selective TPL recognition, regardless of the coating conjugates design. The sensitivity (IC50) of 4 enzyme-linked immunosorbent assays (ELISAs) for TPL varied little within the 3.5-7.4 ng/mL, with a dynamic range of 0.2-100 ng/mL. RSM was coupled to BSA through several glycoside sites that evoked a wider repertoire of response. This first described anti-RSM antibody was selective for RSM in homologous hapten-coated ELISAs with IC50 values in the range 4.2-35 ng/mL. Among the heterologous antigens, periodate-oxidized TPL conjugated to gelatine was selected as the best binder of generic anti-RSM fraction. The developed ELISA showed group recognition of glycopeptides RSM, TPL, eremomycin, and vancomycin with cross-reactivity of 37-100% and a 10-10,000 ng/mL dynamic range. Thus, multiple presentations of immunizing hapten help expand the repertoire of immune responses and opportunities for the selection of the required fine-specificity agent.

Ciprofloxacin and Clinafloxacin Antibodies for an Immunoassay of Quinolones: Quantitative Structure⁻Activity Analysis of Cross-Reactivities

A common problem in the immunodetection of structurally close compounds is understanding the regularities of immune recognition, and elucidating the basic structural elements that provide it. Correct identification of these elements would allow for select immunogens to obtain antibodies with either wide specificity to different representatives of a given chemical class (for class-specific immunoassays), or narrow specificity to a unique compound (mono-specific immunoassays). Fluoroquinolones (FQs; antibiotic contaminants of animal-derived foods) are of particular interest for such research. We studied the structural basis of immune recognition of FQs by antibodies against ciprofloxacin (CIP) and clinafloxacin (CLI) as the immunizing hapten. CIP and CLI possess the same cyclopropyl substituents at the N1 position, while their substituents at C7 and C8 are different. Anti-CIP antibodies were specific to 22 of 24 FQs, while anti-CLI antibodies were specific to 11 of 26 FQs. The molecular size was critical for the binding between the FQs and the anti-CIP antibody. The presence of the cyclopropyl ring at the N1 position was important for the recognition between fluoroquinolones and the anti-CLI antibody. The anti-CIP quantitative structure–activity relationship (QSAR) model was well-equipped to predict the test set (pred_R² = 0.944). The statistical parameters of the anti-CLI model were also high (R² = 0.885, q² = 0.864). Thus, the obtained QSAR models yielded sufficient correlation coefficients, internal stability, and predictive ability. This work broadens our knowledge of the molecular mechanisms of FQs’ interaction with antibodies, and it will contribute to the further development of antibiotic immunoassays.

[The question about the topical antibiotic therapy of acute rhinosinusitis]

Presented the results of the clinical study of 30 patients with moderate rhinosinusitis (13 (43.3%) men, 17 (56.7%) women, age from 18 to 68 years). Among those patients, the inflammation of one paranasal sinus was observed in 7 (23.3%) cases, polysinusitis was observed in 23 (76. 7%) cases. All patients were randomized into 2 groups of 15 people. In both groups, patients received systemic antibiotic therapy, nasal irrigation therapy, and NSAIDs. In the control group, topical decongestants were used; in the experimental group the antimicrobial drug Polydexa with phenylephrine was used as a local therapy. The purpose of the study was to evaluate the clinical efficacy of Polydexa with phenylephrine in the complex treatment of moderate acute rhinosinusitis. The evaluation criteria were statistically significant comparison of clinical and laboratory parameters of both groups. Confirmed the anti-inflammatory, antimicrobial effects of the drug, made conclusions about the significant clinical efficacy, tolerability, positive effect on mucociliary clearance and safety of nasal spray Polydexa with phenylephrine.

Development of a surface plasmon resonance immunosensor and ELISA for 3-nitrotyrosine in human urine

3-Nitrotyrosine (3-NT) is thought to be a relevant biomarker of nitrosative stress which is associated with many inflammatory and chronic diseases. It is necessary to develop confidential method for specific and sensitive 3-NT detection. In this paper, on the basis of anti-3-NT specific antibody, we developed a label-free indirect competitive surface plasmon resonance (SPR) immunosensor and ELISA for the detection of 3-NT. Under the optimized conditions, the SPR immunosensor can obtain a linear range of 0.17-6.07 μg/mL and a limit of detection (LOD) of 0.12 μg/mL while the ELISA can reach 0.33-9.94 μg/mL and a LOD of 0.24 μg/mL.The selectivity of 3-NT was also testified by six kinds of amino acid analogues. Besides, the developed SPR immunosensor was compared thoroughly with a conventional ELISA in spiked analysis of urine samples. Good recoveries and correlation between these two methods were observed (R² = 0.964). Therefore, it is concluded that the automated SPR platform can be applied to quantify 3-NT in biological samples with its sensitivity, accuracy, and real-timing.

Ultrasensitive electrochemical immuno-sensing platform based on gold nanoparticles triggering chlorpyrifos detection in fruits and vegetables

Chlorpyrifos (chl) is an organophosphate pesticide extensively used in agriculture and highly toxic for human health. Fluorine doped tin-oxide (FTO) based electrochemical nanosensor was developed for chlorpyrifos detection with gold nanoparticles (AuNPs) and anti-chlorpyrifos antibodies (chl-Ab). AuNPs provides high electrical conductivity and specific resistivity, thus increases the sensitivity of immunoassay. High electrical conductivity of AuNPs reveals that it promotes the redox reaction for better cyclic voltammetry. Based on the intrinsic conductive properties of FTO-AuNPs complex, chl-Ab was immobilized onto AuNPs surface. Under optimized conditions, the proposed FTO based nanosensor exhibited high sensitivity and stable response for the detection of chlorpyrifos, ranging from 1fM to 1µM with limit of detection (LOD) up to 10fM. The FTO-AuNPs sensor was successfully employed for the detection of chlorpyrifos in standard as well in real samples up to 10nM for apple and cabbage, 50nM for pomegranate. The proposed FTO-AuNPs nanosensor can be used as a quantitative tool for rapid, on-site detection of chlorpyrifos traces in real samples when miniaturized due to its excellent stability, sensitivity, and simplicity.

A gold nanoparticle-single-chain fragment variable antibody as an immunoprobe for rapid detection of morphine by dipstick

Gold nanoparticle (AuNP)-based optical assays are of significant interest since the molecular phenomenon can be examined easily with change in the color of AuNPs. Herein, we report the development of a dipstick using a AuNP-labeled single-chain fragment variable (scFv) antibody for the detection of morphine. The scFv antibodies for morphine were developed using phage display-based antibody library. Immunoglobulin variable regions of heavy (V_H)- and light (V_L)-chain genes were connected via a glycine–serine linker isolated from murine immune repertoire and cloned into the expression vector pIT2. The scFv was produced in Escherichia coli HB2151, yielding a functional protein with a molecular weight of approximately 32 kDa. The morphine scFv was labeled with gold nanoparticles and used as an optical immunoprobe in a dipstick. The competitive dipstick assay characterized the ability of the scFv antibody to recognize free morphine. The detection range was 1–1000 ng mL⁻¹ with a limit of detection (LOD) of 5 ng mL⁻¹ under optimal conditions, and the IC₅₀ value was 14 ng mL⁻¹ for morphine. The developed optical dipstick kit of scFv antibody was capable of specifically binding to free morphine and its analogs in a solution in less than 5 min and could be useful for on-site screening of a real sample in blood, urine, and saliva.

Dipstick device developed on the principle of lateral flow using gold nanoparticles for analysis of morphine in urine by morphine/scFv/immunoprobe.

Broad-Specificity Immunoassay for Simultaneous Detection of Ochratoxins A, B, and C in Millet and Maize

Ochratoxins A, B, and C (OTA, OTB, and OTC) can be found in cereals and feeds; the simultaneous detection of these ochratoxins holds a great need in food safety. In this study, four antibodies raised from two ochrotoxin haptens and two coating antigens were compared, and then a sensitive and broad-specificity enzyme-linked immunosorbent assay (ELISA) was established for the simultaneous determination of three ochratoxins, where the detection limits were 0.005, 0.001, and 0.001 ng/mL for OTA, OTB, and OTC, respectively, and recoveries of three ochratoxins were between 84.3% and 111.7%. This developed method had been successfully applied to detect ochratoxins in both millet and maize. Molecular modeling revealed that the broad-specificity was related with the chlorine electronegativity on OTA and OTC and the potential of the acetyl ester group on OTC. The proposed ELISA can be used for simultaneous detection of three ochratoxins.

Fluorescence Polarization Immunoassay Based on a New Monoclonal Antibody for the Detection of the Zearalenone Class of Mycotoxins in Maize

To develop a sensitive fluorescence polarization immunoassay (FPIA) for screening the zearalenone class of mycotoxins in maize, two new monoclonal antibodies with uniform affinity to the zearalenone class and four fluorescein-labeled tracers were prepared. After careful selection of appropriate tracer-antibody pairs in terms of sensitivity and specificity, a FPIA that could simultaneously detect the zearalenone class with similar sensitivity was developed. Under optimum conditions, the half maximal inhibitory concentrations of the FPIA in buffer were 1.89, 1.97, 2.43, 1.99, 2.27, and 2.44 μg/L for zearalenone, α-zearalenol, β-zearalenol, α-zearalanol, β-zearalanol, and zearalanone, respectively. The limit of detection of FPIA for the zearalenone class was around 12 μg/kg in maize, and the recoveries ranged from 84.6 to 113.8%, with coefficients of variation below 15.3% in spiked samples. Finally, the FPIA was applied for screening naturally contaminated maize samples, and the results indicated a good correlation with that of high-performance liquid chromatography-tandem mass spectrometry.

Use of anchor protein modules in fluorescence polarisation aptamer assay for ochratoxin A determination

A new strategy for sensitive fluorescence polarisation (FP) analysis is proposed which uses aptamer as the receptor and anchor protein modules as the enhancers by including the aptamers in complexes with protein modules. This approach is based on increasing the size differences of bound and unbound fluorophores. The strategy was applied in an ochratoxin A (ОТА) assay with the competitive binding of fluorophore-labelled and free OTA with aptamer-based receptors. We showed that the binding of labelled OTA with aptamer included in complexes with anchors led to higher a FP than binding with free aptamer. This allowed the aptamer concentration to be reduced, thus lowering the limit of detection by a factor of 40, down to 3.6 nM. The assay time was 15 min. To evaluate the applicability of the FP assay with aptamer-anchor complex to real samples, we conducted OTA measurements in spiked white wine. The OTA limit of detection in wine was 2.8 nM (1.1 μg/kg), and the recoveries ranged from 83% to 113%. The study shows that the proposed anchor strategy is efficient for increasing the sensitivity of FP-based aptamer assays.

Detection of kanamycin and gentamicin residues in animal-derived food using IgY antibody based ic-ELISA and FPIA

Our aim in this study is to show that IgY antibody based immunoassays could be used to detect antibiotic residues in animal-derived food. Briefly, full antigens of gentamicin (Gent) and kanamycin (Kana) were used to immunize the laying chickens to prepare IgY antibodies. Then, these antibodies were evaluated by FPIA and ic-ELISA to detect Gent/Kana in animal-derived samples. The IC₅₀ of FPIA and ic-ELISA based anti-Gent IgY were 7.70±0.6μg/mL and 0.32±0.06μg/mL, respectively. The IC₅₀ of FPIA and ic-ELISA based anti-Kana IgY were 7.97±0.9μg/mL and 0.15±0.01μg/mL. The limits of detection (LOD, IC₁₀) for FPIA based anti-Gent/Kana IgY were 0.17 and 0.007μg/mL, respectively. The LOD for ic-ELISA were both 0.001μg/mL. These results indicated that the ic-ELISA might more suitable for antibiotic residues detection than FPIA.

Chemiluminescence Resonance Energy Transfer Competitive Immunoassay Employing Hapten-Functionalized Quantum Dots for the Detection of Sulfamethazine

We describe a new strategy for using chemiluminescence resonance energy transfer (CRET) by employing hapten-functionalized quantum dots (QDs) in a competitive immunoassay for detection of sulfamethazine (SMZ). Core/multishell QDs were synthesized and modified with phospholipid-PEG. The modified QDs were functionalized with the hapten 4-(4-aminophenyl-sulfonamido)butanoic acid. The CRET-based immunoassay exhibited a limit of detection for SMZ of 9 pg mL(-1), which is >4 orders of magnitude better than a homogeneous fluorescence polarization immunoassay and is 2 orders of magnitude better than a heterogeneous enzyme-linked immunosorbent assay. This strategy represents a simple, reliable, and universal approach for detection of chemical contaminants.

Heterologous strategy enhancing the sensitivity of the fluorescence polarization immunoassay of clinafloxacin in goat milk

BACKGROUND

Clinafloxacin is used for the treatment of disease in food-producing animals, e.g. Brucella melitensis, which often occurs in goats; however, the clinafloxacin residue in goat milk may harm human health and result in the development of drug-resistant bacterial strains or allergies. Despite this, there is not a rapid, sensitive and accurate analytical method in goat milk for rapid screening or monitoring purposes.

RESULTS

One homologous and five heterologous tracers were designed and compared for fluorescence polarization immunoassay (FPIA) optimization. Based on the combination of a heterologous tracer (PAZ-FITC, synthesized with pazufloxacin and FITC) and the antibody against clinafloxacin, a highly sensitive FPIA was established for the detection of clinafloxacin residue in goat milk for the first time. The IC50 value was 29.3 µg L(-1) for clinafloxacin in the heterologous format - six times lower than that of the combination of the homologous tracers and the antibody. The recoveries ranged from 86.8% to 104.5%, with the relative standard deviation ranging from 4.1% to 7.2%. Validation by high-performance liquid chromatography (HPLC) confirmed that the results obtained from the proposed FPIA were in agreement with those of HPLC.

CONCLUSION

This proposed heterologous strategy for enhanced FPIA is sensitive and rapid enough for the high-throughput detection of clinafloxacin residue in goat milk.