Development of immunoassays for multi-residue detection of small molecule compounds

Detection of foodborne pathogens in contaminated food using nanomaterial-based electrochemical biosensors

Foodborne pathogens are a grave concern for the for food, medical, environmental, and economic sectors. Their ease of transmission and resistance to treatments, such as antimicrobial agents, make them an important challenge. Food tainted with these pathogens is swiftly rejected, and if ingested, can result in severe illnesses and even fatalities. This review provides and overview of the current status of various pathogens and their metabolites transmitted through food. Despite a plethora of studies on treatments to eradicate and inhibit these pathogens, their indiscriminate use can compromise the sensory properties of food and lead to contamination. Therefore, the study of detection methods such as electrochemical biosensors has been proposed, which are devices with advantages such as simplicity, fast response, and sensitivity. However, these biosensors may also present some limitations. In this regard, it has been reported that nanomaterials with high conductivity, surface-to-volume ratio, and robustness have been observed to improve the detection of foodborne pathogens or their metabolites. Therefore, in this work, we analyze the detection of pathogens transmitted through food and their metabolites using electrochemical biosensors based on nanomaterials.

Antibody-Bridged DNAzyme Walker for Sensitive Detection of Small Molecules

Sensitive detection of small molecules with biological and environmental interests is important for many applications, such as food safety, disease diagnosis, and environmental monitoring. Herein, we propose a highly selective antibody-bridged DNAzyme walker to sensitively detect small molecules. The antibody-bridged DNAzyme walker consists of a track, small-molecule-labeled DNAzyme walking strand, and antibody against small molecules. The track is built by co-modifying fluorophore-labeled substrates and small-molecule-labeled DNA linkers onto a gold nanoparticle (AuNP). In the absence of the target molecule, the antibody binds small molecule labels at the DNAzyme walking strand and the DNA linker, driving the DNAzyme walking strand on the surface of the AuNP. The attached DNAzyme walking strand moves along the track and cleaves substrates to generate high fluorescence signals to achieve signal amplification. As target molecules exist, they competitively bind with antibody to displace the small-molecule-labeled linker and DNAzyme walking strand, rendering the DNAzyme walker inactive in substrate cleavage and causing weak fluorescence. By using this antibody-bridged DNAzyme walker, we achieved sensitive detection of two biologically important small molecules, digoxin and folic acid. This work provides a new paradigm by combining the signal amplification strategy of a DNA walker and immunorecognition for sensitive and selective detection of small molecules.

Different sized gold nanoparticles for array-based sensing of pesticides and its application for strawberry pollution monitoring

The use of pesticides plays an essential role in improving crop quality and yield, however, it causes air, water, and soil pollution and the residue of these pesticides in agricultural products threatens the ecosystem and human life. Therefore, it is highly desirable to develop rapid, simple, and cost-effective methods for regular monitoring of pesticide residues in agricultural products especially strawberry that is consumed fresh and unpeeled. In this study, gold nanoparticles (AuNPs) of varying sizes have been exploited as sensing units to design a non-enzymatic colorimetric sensor array for the detection and discrimination of various pesticides including; bifenazate (BF), paraquat (PQ), diazinon (DZ), thiometon (TM), and carbendazim (CD) and chlorpyrifos (CP). Because of their strong size- and environmentally-dependent properties, AuNPs with different sizes produced distinguished plasmonic patterns in the presence of pesticides at a vast range of concentrations (25-800 ng mL-1). Plasmonic patterns of sensor units have been analyzed by various data visualization (bar plots and heat maps) and pattern recognition methods (linear discriminant analysis (LDA)). The multivariate calibrations showed linear responses ranging from 50 to 800 ng mL-1 for carbendazim, chlorpyrifos, paraquat, and bifenazate and 25-800 ng mL-1 for diazinon and thiometon. The limit of detection (LOD) was calculated to be 17.7, 22.8, 22.4, 9.7, 7.4, and 23.8 ng mL-1 for carbendazim, chlorpyrifos, paraquat, diazinon, thiometon, and bifenazate respectively. Finally, the applicability of the designed sensor was evaluated in real samples comprising tap water, well water, soil, and fruit, leave, drainage water, and culture substrate of strawberry.

Competitive fluorescent immunosensor based on catalytic hairpin self-assembly for multiresidue detection of organophosphate pesticides in agricultural products

Simple and rapid multiresidue trace detection of organophosphate pesticides (OPs) is extremely important for various reasons, including food safety, environmental monitoring, and national health. Here, a catalytic hairpin self-assembly (CHA)-based competitive fluorescent immunosensor was developed to detect OPs in agricultural products, involving enabled dual signal amplification followed by a CHA reaction. The developed method could detect 0.01-50 ng/mL triazophos, parathion, and chlorpyrifos, with limits of detection (LODs) of 0.012, 0.0057, and 0.0074 ng/mL, respectively. The spiked recoveries of samples measured using this assay ranged from 82.8 % to 110.6 %, with CV values ranging between 5.5 % and 18.5 %. This finding suggests that the CHA-based competitive fluorescent immunosensor is a reliable and accurate method for detecting OPs in agricultural products. The results correlated well with those obtained from the liquid chromatography-tandem mass spectrometry (LC-MS/MS) method, indicating that the CHA-based biosensor is able to accurately detect OPs and can be used as a reliable alternative to the LC-MS/MS method. Additionally, the CHA-based biosensor is simpler and faster than LC-MS/MS, which makes it a more practical and cost-effective option for the detection of OPs. In summary, the CHA-based competitive fluorescent immunosensor can be considered a promising approach for trace analysis and multiresidue determination of pesticides, which can open up new horizons in the fields of food safety, environmental monitoring, and national health.

The application of rapid test paper technology for pesticide detection in horticulture crops: a comprehensive review

Background

The ever increasing pests and diseases occurring during vegetable crop production is a challenge for agronomists and farmers. One of the practices to avoid or control the attack of the causal agents is the use of pesticides, including herbicides, insecticides nematicides, and molluscicides. However, the use of these products can result in the presence of harmful residues in horticultural crops, which cause several human diseases such as weakened immunity, splenomegaly, renal failure, hepatitis, respiratory diseases, and cancer. Therefore, it was necessary to find safe and effective techniques to detect these residues in horticultural crops and to monitor food security.

Main body

The review discusses the use of conventional methods to detect pesticide residues on horticultural crops, explain the sensitivity of nanoparticle markers to detect a variety of pesticides, discuss the different methods of rapid test paper technology and highlight recent research on rapid test paper detection of pesticides.

Conclusions

The methodologies discussed in the current review can be used in a certain situation, and the variety of methods enable detection of different types of pesticides in the environment. Notably, the highly sensitive immunoassay, which offers the advantages of being low cost, highly specific and sensitive, allows it to be integrated into many detection fields to accurately detect pesticides.

Highly sensitive and multiplexed mass spectrometric immunoassay techniques and clinical applications

Immunoassay is one of the most important clinical techniques for disease/pathological diagnosis. Mass spectrometry (MS) has been a popular and powerful readout technique for immunoassays, generating the mass spectrometric immunoassays (MSIAs) with unbeatable channels for multiplexed detection. The sensitivity of MSIAs has been greatly improved with the development of mass labels from element labels to small-molecular labels. MSIAs are also expended from the representative element MS-based methods to the laser-based organic MS and latest ambient MS, improving in both technology and methodology. Various MSIAs present high potential for clinical applications, including the biomarker screening, the immunohistochemistry, and the advanced single-cell analysis. Here, we give an overall review of the development of MSIAs in recent years, highlighting the latest improvement of mass labels and MS techniques for clinical immunoassays.

High-Throughput Detection of Multiple Contaminants Based on Portable Photoelectrochromic Sensor Chip

With the increasing concerns about the environment and food safety, it is necessary to develop portable, low-cost, and high-throughput biosensors for the simultaneous detection of multiple contaminates. However, traditional photoelectrochemical (PEC) biosensors lack the ability of multiplexed assays due to the inherent mechanism limitation. Also, specialized instruments are necessary for most PEC biosensors. In this work, a portable high-throughput sensor chip has been successfully developed. By introducing electrochromic materials, the detection is based on color change instead of electric signals, which reduces the limitation of instruments. This designed sensor chip is composed of three parallel sensing channels fabricated by laser etching. Each channel is modified with TiO₂/3D-g-C₃N₄ composites with excellent PEC activity and electrochromic material Prussian blue (PB). Under light illumination, photoinduced electrons generated by TiO₂/3D-g-C₃N₄ are injected into PB, and blue PB is reduced to colorless Prussian white. Three organic contaminates, ochratoxin A, lincomycin, and edifenphos, can be simultaneously detected because the binding of these molecules with aptamers affects the electron transfer and the corresponding color changes. This portable and high-throughput sensor chip provides a convenient choice for multiplexed assays with good sensitivity and accuracy.

Enhanced Bio-Barcode Immunoassay Using Droplet Digital PCR for Multiplex Detection of Organophosphate Pesticides

A bio-barcode immunoassay based on droplet digital polymerase chain reaction (ddPCR) was developed to simultaneously quantify triazophos, parathion, and chlorpyrifos in apple, cucumber, cabbage, and pear. Three gold nanoparticle (AuNP) probes and magnetic nanoparticle (MNP) probes were prepared, binding through their antibodies with the three pesticides in the same tube. Three groups of primers, probes, templates, and three antibodies were designed to ensure the specificity of the method. Under the optimal conditions, the detection limits (expressed as IC₁₀) of triazophos, parathion, and chlorpyrifos were 0.22, 0.45, and 4.49 ng mL^-1, respectively. The linear ranges were 0.01-20, 0.1-100, and 0.1-500 ng mL^-1, and the correlation coefficients (R²) were 0.9661, 0.9834, and 0.9612, respectively. The recoveries and relative standard deviations (RSDs) were in the ranges of 75.5-98.9 and 8.3-16.7%. This study provides the first insights into the ddPCR for the determination of organophosphate pesticides. It also laid the foundation for high-throughput detection of other small molecules.

Immunoassay-based approaches for development of screening of chlorpyrifos

Chlorpyrifos (CPF) is an extensively used organophosphate pesticide for crop protection. However, there are concerns of it contaminating the environment and human health with estimated three lakh deaths annually. Detection of CPF in blood samples holds significance to avoid severe health outcomes due to continuous exposure. The most common techniques for CPF detection are Gas chromatography (GC) and high-performance liquid chromatography (HPLC). However, these techniques might not be feasible at the community healthcare level due to high-cost instrumentation, time-consuming sample preparation protocol and skilled analysts. Therefore, rapid, effective and economical methods such as immunoassay would be imperative for CPF detection in biological samples. The vital step in immunoassay development is the design of a potent immunogen from non-immunogenic molecules. The molecular modelling protocol could assist in redesigning known CPF linkers and inserting them at different substitutable positions of CPF to get distinctive CPF derivatives. Molecular docking and binding free energy analysis can be used to identify the CPF derivatives having a better binding affinity with carrier protein compared to CPF. The top-ranked CPF derivatives based on docking score and binding energy could be ideal for synthesis and immunogen development. The present review will comprehend technological trends in immunoassay kits for detecting chlorpyrifos from biological samples.

Simultaneous determination of ochratoxin A and enterotoxin A in milk by magnetic nanoparticles based fluorescent immunoassay

Ochratoxin A (OTA) and staphylococcus enterotoxin A (SEA) are highly toxic contaminants and have induced human health problems. They commonly occur in milk and milk products. A competitive fluorescent immunoassay was developed for rapid and simultaneous determination of these toxins in milk samples. The procedure was based on the competitive immunoreactions between antigens in sample and antigen-fluorescent dye conjugates with immobilised antibodies on magnetic nanoparticles (MNPs). Each monoclonal antibody specifically recognises its corresponding toxin (antigen), and there is no cross-reactivity in the assay. First, monoclonal antibodies against OTA and SEA were produced. The activity of the obtained antibodies was determined by fluorescent-linked immunosorbent assay. Then, the monoclonal antibodies were immobilised on MNPs. The amounts of immobilised anti-OTA antibody and anti-SEA antibody were determined to be 20 and 22 μg mL^-1, respectively. The antigen-fluorescent dye conjugates OTA-OVA-ATTO620 and SEA-FITC were prepared. The optimal amount of immobilised antibodies for competitive immunoassay was determined. It was found that the linear range of OTA in buffer was larger (0.001-100 ng mL^-1) than the linear range of SEA (0.001-20 ng mL^-1). The results for simultaneous determination of OTA and SEA in sixfold diluted milk were almost the same in buffer; the linear range for OTA was from 0.005  to 100 ng mL^-1 and for SEA from 0.005  to 20 ng mL^-1. The detection limit for both OTA and SEA in milk was 0.004 ng mL^-1. The developed method took half the time of the individual assays (20 min). The assay was evaluated using spiked milk samples. The influences of somatic cell count, fat, pH and protein concentration in milk on immunoassay were studied. In summary, this developed immunoassay could provide an effective and rapid approach for detecting multi-toxins in milk samples.

Microcystin-LR heterologous genetically engineered antibody recombinant and its binding activity improvement and application in immunoassay

Microcystin-LR (MC-LR) is a high-toxic biohazard that pollutes ecological environment and agroproducts. In this study, a newly recombined genetically engineered antibody (AV_HH-MV_H) with higher thermal stability and binding activity was designed by chain shuffling and based on our previously obtained anti-MC-LR scFv and nanobody. Based on AV_HH-MV_H template, a capacity of 8.99 × 10⁵ CFU/mL of phage display AV_HH-MV_H mutagenesis library was constructed by site-directed mutagenesis in MV_H-CDR3 region, and then used for ultrasensitive mutants screening. Afterwards, a total of five positive AV_HH-MV_H mutants were isolated from the mutagenesis library, and their binding activity was higher than AV_HH-MV_H for MC-LR. The AV_HH-MV_H mutant 3 was cloned into pET-25b vector for soluble expression, and the concentration of target protein expressed in culture system was 43.5 mg/L. An indirect competitive enzyme-linked immunosorbent assay (IC-ELISA) was established based on purified AV_HH-MV_H mutant 3 protein, and it showed ultrasensitive binding activity for MC-LR with the detection limit of 0.0075 μg/L, which was far below the maximum residue limit standard of 1.0 μg/L in drinking water proposed by World Health Organization. The established IC-ELISA shows good accuracy, repeatability, stability and applicability for MC-LR spiked samples, and it is promising for MC-LR ultrasensitive monitoring.

A general strategy to control antibody specificity against targets showing molecular and biological similarity: Salmonella case study

The control of antibody specificity plays pivotal roles in key technological fields such as diagnostics and therapeutics. During the development of immunoassays (IAs) for the biosensing of pathogens in food matrices, we have found a way to rationalize and control the specificity of polyclonal antibodies (sera) for a complex analytical target (the Salmonella genus), in terms of number of analytes (Salmonella species) and potential cross-reactivity with similar analytes (other bacteria strains). Indeed, the biosensing of Salmonella required the development of sera and serum mixtures displaying homogeneous specificity for a large set of strains showing broad biochemical variety (54 Salmonella serovars tested in this study), which partially overlaps with the molecular features of other class of bacteria (like specific serogroups of E. coli). To achieve a trade-off between specificity harmonisation and maximization, we have developed a strategy based on the conversion of the specificity profiles of individual sera in to numerical descriptors, which allow predicting the capacity of serum mixtures to detect multiple bacteria strains. This approach does not imply laborious purification steps and results advantageous for process scaling-up, and may help in the customization of the specificity profiles of antibodies needed for diagnostic and therapeutic applications such as multi-analyte detection and recombinant antibody engineering, respectively.

A Two-Dimensional Affinity Capture and Separation Mini-Platform for the Isolation, Enrichment, and Quantification of Biomarkers and Its Potential Use for Liquid Biopsy

Biomarker detection for disease diagnosis, prognosis, and therapeutic response is becoming increasingly reliable and accessible. Particularly, the identification of circulating cell-free chemical and biochemical substances, cellular and subcellular entities, and extracellular vesicles has demonstrated promising applications in understanding the physiologic and pathologic conditions of an individual. Traditionally, tissue biopsy has been the gold standard for the diagnosis of many diseases, especially cancer. More recently, liquid biopsy for biomarker detection has emerged as a non-invasive or minimally invasive and less costly method for diagnosis of both cancerous and non-cancerous diseases, while also offering information on the progression or improvement of disease. Unfortunately, the standardization of analytical methods to isolate and quantify circulating cells and extracellular vesicles, as well as their extracted biochemical constituents, is still cumbersome, time-consuming, and expensive. To address these limitations, we have developed a prototype of a portable, miniaturized instrument that uses immunoaffinity capillary electrophoresis (IACE) to isolate, concentrate, and analyze cell-free biomarkers and/or tissue or cell extracts present in biological fluids. Isolation and concentration of analytes is accomplished through binding to one or more biorecognition affinity ligands immobilized to a solid support, while separation and analysis are achieved by high-resolution capillary electrophoresis (CE) coupled to one or more detectors. When compared to other existing methods, the process of this affinity capture, enrichment, release, and separation of one or a panel of biomarkers can be carried out on-line with the advantages of being rapid, automated, and cost-effective. Additionally, it has the potential to demonstrate high analytical sensitivity, specificity, and selectivity. As the potential of liquid biopsy grows, so too does the demand for technical advances. In this review, we therefore discuss applications and limitations of liquid biopsy and hope to introduce the idea that our affinity capture-separation device could be used as a form of point-of-care (POC) diagnostic technology to isolate, concentrate, and analyze circulating cells, extracellular vesicles, and viruses.

Design of Multiplex Lateral Flow Tests: A Case Study for Simultaneous Detection of Three Antibiotics

The presented study is focused on the impact of binding zone location on immunochromatographic test strips on the analytical parameters of multiplex lateral flow assays. Due to non-equilibrium conditions for such assays the duration of immune reactions influences significantly the analytical parameters, and the integration of several analytes into one multiplex strip may cause an essential decrease of sensitivity. To choose the best location for binding zones, we have tested reactants for immunochromatographic assays of lincomycin, chloramphenicol, and tetracycline. The influence of the distance to the binding zones on the intensity of coloration and limit of detection (LOD) was rather different. Basing on the data obtained, the best order of binding zones was chosen. In comparison with non-optimal location the LODs were 5–10 fold improved. The final assay provides LODs 0.4, 0.4 and 1.0 ng/mL for lincomycin, chloramphenicol, and tetracycline, respectively. The proposed approach can be applied for multiplexed assays of other analytes.

Monitoring pharmaceuticals in the aquatic environment using enzyme-linked immunosorbent assay (ELISA)-a practical overview

The presence of pharmaceuticals, which are considered as contaminants of emerging concern, in natural waters is currently recognized as a widespread problem. Monitoring these contaminants in the environment has been an important field of research since their presence can affect the ecosystems even at very low levels. Several analytical techniques have been developed to detect and quantify trace concentrations of these contaminants in the aquatic environment, namely high-performance liquid chromatography, gas chromatography, and capillary electrophoresis, usually coupled to different types of detectors, which need to be complemented with time-consuming and costly sample cleaning and pre-concentration procedures. Generally, the enzyme-linked immunosorbent assay (ELISA), as other immunoassay methodologies, is mostly used in biological samples (most frequently urine and blood). However, during the last years, the number of studies referring the use of ELISA for the analysis of pharmaceuticals in complex environmental samples has been growing. Therefore, this work aims to present an overview of the application of ELISA for screening and quantification of pharmaceuticals in the aquatic environment, namely in water samples and biological tissues. The experimental procedures together with the main advantages and limitations of the assay are addressed, as well as new incomes related with the application of molecular imprinted polymers to mimic antibodies in similar, but alternative, approaches. Graphical Abstract.

An Electrochemical Fiveplex Biochip Assay Based on Anti-Idiotypic Antibodies for Fast On-Site Detection of Bioterrorism Relevant Low Molecular Weight Toxins

Modern threats of bioterrorism force the need for multiple detection of biothreat agents to determine the presence or absence of such agents in suspicious samples. Here, we present a rapid electrochemical fiveplex biochip screening assay for detection of the bioterrorism relevant low molecular weight toxins saxitoxin, microcystin-LR, T-2 toxin, roridin A and aflatoxin B1 relying on anti-idiotypic antibodies as epitope-mimicking reagents. The proposed method avoids the use of potentially harmful toxin-protein conjugates usually mandatory for competitive immunoassays. The biochip is processed and analyzed on the automated and portable detection platform pBDi within 13.4 min. The fiveplex biochip assay revealed toxin group specificity to multiple congeners. Limits of detection were 1.2 ng/mL, 1.5 ng/mL, 0.4 ng/mL, 0.5 ng/mL and 0.6 ng/mL for saxitoxin, microcystin-LR, T-2 toxin, roridin A or aflatoxin B1, respectively. The robustness of the fiveplex biochip for real samples was demonstrated by detecting saxitoxin, microcystin-LR, HT-2 toxin, roridin A and aflatoxin B1 in contaminated human blood serum without elaborate sample preparation. Recovery rates were between 52–115% covering a wide concentration range. Thus, the developed robust fiveplex biochip assay can be used on-site to quickly detect one or multiple low molecular weight toxins in a single run.