Non-competitive immunoassay for low-molecular-weight contaminant detection in food, feed and agricultural products: A mini-review

Methods and applications of noncompetitive hapten immunoassays

Hapten immunoassays have found extensive application across various domains such as disease diagnostics, environmental monitoring, as well as the evaluation of food and pharmaceutical safety. These techniques traditionally rely on competitive assay formats and often face challenges with sensitivity and specificity. This review focuses on the emergent noncompetitive immunoassay technologies that promise to transcend these limitations through innovative approaches. Noncompetitive immunoassays, leveraging novel elements such as anti-idiotype antibodies, anti-immunocomplex (IC) antibodies, and the strategic use of nanomaterial-enhanced signal detection, are setting new benchmarks for analytical performance. These advancements not only enhance the detection capabilities but also significantly improve specificity inherent in traditional methods. Moreover, the integration of novel materials and binding reagents in these assays offers substantial improvements in assay dynamics, providing faster, more accurate, and reliable results. This review consolidates the latest methodologies and their applications, underlining the transformative impact of noncompetitive technologies in the sensitive detection of haptens across various fields.

Emerging biosensor probes for glycated hemoglobin (HbA1c) detection

Glycated hemoglobin (HbA1c), originating from the non-enzymatic glycosylation of βVal1 residues in hemoglobin (Hb), is an essential biomarker indicating average blood glucose levels over a period of 2 to 3 months without external environmental disturbances, thereby serving as the gold standard in the management of diabetes instead of blood glucose testing. The emergence of HbA1c biosensors presents affordable, readily available options for glycemic monitoring, offering significant benefits to small-scale laboratories and clinics. Utilizing nanomaterials coupled with high-specificity probes as integral components for recognition, labeling, and signal transduction, these sensors demonstrate exceptional sensitivity and selectivity in HbA1c detection. This review mainly focuses on the emerging probes and strategies integral to HbA1c sensor development. We discussed the advantages and limitations of various probes in sensor construction as well as recent advances in diverse sensing strategies for HbA1c measurement and their potential clinical applications, highlighting the critical gaps in current technologies and future needs in this evolving field.

Intramolecular cascade reaction sensing platform for rapid, specific and ultrasensitive detection of nitrite

Nitrite is a carcinogenic substance in food. Excessive consumption of nitrite severely endangers human health. However, rapid and accurate quantification of nitrite by a simple tool is still very challenging. In this work, we designed a practical sensing platform based on 8-(o-phenylenediamine)-boron dipyrromethene (BDP-OPD) to determine nitrite in food. BDP-OPD can take a specific diazotization-cyclization cascade reaction with nitrite to form boron dipyrromethene (BODIPY), giving rise to a remarkable chromogenic reaction along with high contrast fluorescence turn-on response towards nitrite. BDP-OPD has high sensitivity, rapid response, and good selectivity. Furthermore, a portable smartphone-based fluorescence device integrated with a self-programmed Python program was fabricated, which has been successfully used to determine nitrite in food with the advantages of rapid response, low cost, ease of operation, portability, and satisfactory recoveries (92-112%). The good sensing performance rendered BDP-OPD a promising fluorescence platform for on-site visual detection of nitrite.

A breakthrough of immunoassay format for hapten: recent insights into noncompetitive immunoassays to detect small molecules

Immunoassay based on the antibodies specific for targets has advantages of high sensitivity, simplicity and low cost, therefore it has received more attention in recent years, especially for the rapid detection of small molecule chemicals present in foods, diagnostics and environments. However, limited by low molecular weight and only one antigenic determinant existed, immunoassays for these small molecule chemicals, namely hapten substances, were commonly performed in a competitive immunoassay format, whose sensitivities were obviously lower than the sandwich enzyme-linked immunosorbent assay generally adaptable for the protein targets. In order to break through the bottleneck of detection format, researchers have designed and established several novel noncompetitive immunoassays for the haptens in the past few years. In this review, we focused on the four representative types of noncompetitive immunoassay formats and described their characteristics and applications in rapid detection of small molecules. Meanwhile, a systematic discussion on the current technologies challenges and the possible solutions were also summarized. This review aims to provide an updated overview of the current state-of-the-art in noncompetitive immunoassay for small molecules, and inspire the development of novel designs for small molecule detection.

Development of an ultrasensitive sandwich immunoassay for detecting small molecule semicarbazide

Ultrasensitive sandwich immunoassays for detecting the small molecule semicarbazide (SEM) were developed based on derivatization. Several SEM derivatizing agents were synthesized by linking o-nitrobenzaldehyde (NBA) and biotin with dihydroxyalkanes (different lengths), which were then used to evaluate the distance effect of two epitopes. Sandwich ELISA for SEM derivatives was developed using an anti-SEM-NBA antibody and horseradish peroxidase-labeled avidin or anti-biotin antibody as a secondary conjugate. The advantageous distances of the two epitopes under the double-antibody sandwich and antibody-avidin sandwich modes were ≥12 and ≥13 Å, respectively. Under the distances, the sensitivities of the sandwich ELISA were no lower than those of competitive ELISA. The obtained optimal EC50 values were 11.2 pg/mL (double-antibody sandwich with the epitope distance ≥16 Å) and 7.3 pg/mL (antibody-avidin sandwich with the epitope distance ≥17 Å). Compared with competitive ELISA, the developed method achieved a 30-fold improvement in sensitivity, with simpler aquatic product pretreatment.

A Proof-of-Concept Sandwich Enzyme-Linked Immunoassay Development for Small Molecules

A sandwich immunoassay theoretically exhibits higher sensitivity and specificity compared to a competitive counterpart; however, it is extremely difficult to obtain a pair of antibodies that can bind to a small molecule simultaneously, which is always thought to be a single epitope. In the present study, abamectin (ABM) was selected to prove the effect of hapten design and antibody recognition properties on the development of a sandwich immunoassay for small molecules. First, the epitopes of ABM were roughly located, and epitope distances were determined. Then, two haptens were designed by introducing spacer arms at the C4″-OH and C5-OH of ABM, respectively, aiming to provide the longest epitope distances. A total of seven rabbit polyclonal antibodies (pAbs) and 21 mouse monoclonal antibodies (mAbs) with various recognition properties were obtained. Extensive combinatorial associations of antibody pairs for simultaneously binding to ABM were performed, and only two mAb-mAb pairs were observed to achieve a sandwich immunoassay for ABM with a total success rate of 0.27%. The best mAb pair for sandwich immunoassay was confirmed by surface plasmon resonance, used to develop a sandwich immunoassay, and then evaluated by cross-reactivities and molecular docking with structurally similar analogues and abamectin. Altogether, the study provided a theoretical foundation as well as practical experience and demonstrated the importance of careful hapten design and extensive antibody screening to successfully establish the sandwich immunoassay for small molecules.

The Applications of Electrochemical Immunosensors in the Detection of Disease Biomarkers: A Review

Disease-related biomarkers may serve as indicators of human disease. The clinical diagnosis of diseases may largely benefit from timely and accurate detection of biomarkers, which has been the subject of extensive investigations. Due to the specificity of antibody and antigen recognition, electrochemical immunosensors can accurately detect multiple disease biomarkers, including proteins, antigens, and enzymes. This review deals with the fundamentals and types of electrochemical immunosensors. The electrochemical immunosensors are developed using three different catalysts: redox couples, typical biological enzymes, and nanomimetic enzymes. This review also focuses on the applications of those immunosensors in the detection of cancer, Alzheimer's disease, novel coronavirus pneumonia and other diseases. Finally, the future trends in electrochemical immunosensors are addressed in terms of achieving lower detection limits, improving electrode modification capabilities and developing composite functional materials.

Minimum Distance Between Two Epitopes in Sandwich Immunoassays for Small Molecules

The pursuit of the limit between dimensionalities is a scientific goal with high applicability. Sandwich immunoassay, usually based on two antibodies binding two epitopes, is one of the most popular mainstay tools in both academic and industrial fields. Herein, we determined and evaluated the minimum distance of two epitopes in sandwich immunoassays for small molecules. Briefly, nine model analytes comprising two hapten epitopes, that is, melamine (MEL) and p-nitroaniline (NIA), were designed by increasing the linear chain linkers brick by brick. Two groups of monoclonal antibodies (mAbs) were produced with different recognition properties toward MEL and NIA using 12 new haptens with different spacer arms. The results indicated that two epitopes of the analyte with a distance of only 2.4 Å could be simultaneously bound by two mAbs, which is the known limit of epitope distance in sandwich immunoassays thus far. We further found that an epitope distance of below 8.8 Å for the analyte generally induces noticeable steric hindrance of antibodies, preventing a sandwich immunoassay with high probability. These observations were investigated and evaluated by molecular docking, molecular dynamics, and surface plasmon resonance and using model and real analytes. Altogether, we determined the minimum distance of two epitopes and explored the molecular mechanism of the antibody-analyte-antibody ternary complex in sandwich immunoassays, providing a theoretical basis for hapten design, antibody discovery and development, and sandwich immunoassay establishment for small molecules.

Programmable Y-Shaped Probes with Proximity Bivalent Recognition for Rapid Electrochemiluminescence Response of Acute Myocardial Infarction

Herein, an exogenous luminophore-free and disposable electrochemiluminescence (ECL) biosensor was established for rapid response of acute myocardial infarction (AMI) using programmable Y-shaped probes (Y-probes) with proximity bivalent recognition. Specifically, the indium tin oxide thin film coated glass electrode (ITO) was modified with urchin-like porous TiO₂ microspheres (pTiO₂ MSs), which could achieve strong and stable ECL in S₂O₈^2- solution due to the dual promoting effect of the coreaction accelerator pTiO₂ MSs, exhibiting 2.7-fold higher ECL intensity in comparison with that of bare ITO. Moreover, the Y-probes as bivalent recognition elements containing two kinds of cardiac troponin I (cTnI, a biomarker of AMI) aptamers and a linker labeled with ferrocene (L-Fc) were designed to export a "signal off" mode. When the target cTnI was in the proximity of the Y-probes, the L-Fc was separated from the electrode surface due to the proximity recognition of cTnI and its aptamers, achieving the highly effective recovery of ECL, which allowed for a much more rapid detection of cTnI than the sandwich-type immunoassay. As a proof of concept, an exogenous luminophore-free and disposable ECL platform for rapid and sensitive monitoring of cTnI was obtained and displayed a desired linear range from 100 fg mL^-1 to 100 ng mL^-1 with a limit of detection (LOD) of 30.1 fg mL^-1, which can be ingeniously expanded as a portable home tester with ECL biosensors developments.

Double Competitive Immunodetection of Small Analyte: Realization for Highly Sensitive Lateral Flow Immunoassay of Chloramphenicol

A new scheme of reagents interaction for lateral flow immunoassay (LFIA) is proposed, which combines the features of competitive and sandwich assay and provides highly sensitive detection of low-molecular-weight analytes. Namely, the antigen in the sample interferes with the formation of the antibody (on the membrane)–hapten-protein–antibody (on the nanoparticle-marker) complex, competing with hapten-protein conjugate in both reactions. The proposed scheme was modelled using COPASI software, with a prediction of limit of detection (LOD) decrease by one order of magnitude compared to the standard competitive LFIA. This feature was experimentally confirmed for the detection of chloramphenicol (CAP) in honey. When tested in spiked honey, the visual LOD was 50 ng/mL for the common scheme and 5 ng/mL for the proposed scheme. Instrumental LOD was 300 pg/mL (1.2 µg/kg in conversion per sample weight of honey) in the standard scheme and 20 pg/mL (80 ng/kg in conversion per sample weight of honey) in the proposed scheme.

Electrochemical Aptasensors for Antibiotics Detection: Recent Achievements and Applications for Monitoring Food Safety

Antibiotics are often used in human and veterinary medicine for the treatment of bacterial diseases. However, extensive use of antibiotics in agriculture can result in the contamination of common food staples such as milk. Consumption of contaminated products can cause serious illness and a rise in antibiotic resistance. Conventional methods of antibiotics detection such are microbiological assays chromatographic and mass spectroscopy methods are sensitive; however, they require qualified personnel, expensive instruments, and sample pretreatment. Biosensor technology can overcome these drawbacks. This review is focused on the recent achievements in the electrochemical biosensors based on nucleic acid aptamers for antibiotic detection. A brief explanation of conventional methods of antibiotic detection is also provided. The methods of the aptamer selection are explained, together with the approach used for the improvement of aptamer affinity by post-SELEX modification and computer modeling. The substantial focus of this review is on the explanation of the principles of the electrochemical detection of antibiotics by aptasensors and on recent achievements in the development of electrochemical aptasensors. The current trends and problems in practical applications of aptasensors are also discussed.

Identification of single domain antibodies with insect cytotoxicity using phage-display antibody library screening and Plutella xylostella ATP-binding cassette transporter subfamily C member 2 (ABCC2) -based insect cell expression system

It is extremely imminent to study a new strategy to manage agricultural pest like Plutella xylostella (P. xylostella) which is currently resistant to most of pesticides, including three domain-Cry toxins from Bacillus thuringiensis (Bt). In this study, we reported a phage displayed single domain antibody screening from human domain antibody (DAb) library targeted on Spodoptera frugiperda 9 (Sf9) cells expressed Cry1Ac toxin receptor, ATP-dependent binding cassette transporter C2 in P. xylostella (PxABCC2). After three rounds of panning, three cytotoxic antibodies (1D2, 2B7, 3C4) were obtained from thirty-eight antibodies and displayed high binding ability towards PxABCC2-expressed Sf9 cells. Through homology modeling and molecular docking, the interaction mode indicated that the most cytotoxic 1D2 of the three antibodies presented the lowest binding free energy required and had the most hydrogen bond formed with PxABCC2 in molecular docking analysis. Functional assay of key regions in 1D2 via Alanine replacement indicated that complementarity-determining region (CDR) 3 played a crucial role in antibody exerts binding activity and cytotoxicity. This study provides the first trial for discovering of potential cytotoxic antibodies from the human antibody library via specific receptor-expressed insect cell system biopanning.

Development of a noncompetitive magnetic-phage anti-immunocomplex assay for detecting of organophosphorus pesticides with a thiophosphate group

Organophosphorus pesticides (OPs) are widely used in agriculture and the monitoring of their residues is very important to protect human health. Immunoassays are important tools for the analysis of small molecules. Generally, noncompetitive mode of immunoassay is considered to be more sensitive than competitive mode. In this study, peptides that can identify immunocomplex of OPs were screened from a phage display library. Subsequently, a second-generation peptide library was constructed and peptides with better performance were isolated. Then, a rapid and sensitive noncompetitive magnetic-phage anti-immunocomplex assay (MPHAIA) for OPs was developed based on the best phage-peptide and single chain antibody immunomagnetic beads. The MPHAIA showed broad specificity for OPs with a thiophosphate group. The half-saturated concentration (SC₅₀) values and limits of detection (LODs) of MPHAIA to 12 OPs were ranged from 15.04 to 105.48 ng/mL and 4.07-14.19 ng/mL, respectively. The accuracy and reliability of MPHAIA were verified by gas chromatography-tandem mass spectrometry (GC-MS/MS) parallel analysis of six kinds of OPs in spiked cucumber samples. The recovery rates were in range of 81.2-116.3% with coefficient of variation from 4.1% to 14.1%, which were consistent with the results of GC-MS/MS.

Immunological Analytical Techniques for Cosmetics Quality Control and Process Monitoring

Cosmetics analysis represents a rapidly expanding field of analytical chemistry as new cosmetic formulations are increasingly in demand on the market and the ingredients required for their production are constantly evolving. Each country applies strict legislation regarding substances in the final product that must be prohibited or regulated. To verify the compliance of cosmetics with current regulations, official analytical methods are available to reveal and quantitatively determine the analytes of interest. However, since ingredients, and the lists of regulated/prohibited substances, rapidly change, dedicated analytical methods must be developed ad hoc to fulfill the new requirements. Research focuses on finding innovative techniques that allow a rapid, inexpensive, and sensitive detection of the target analytes in cosmetics. Among the different methods proposed, immunological techniques are gaining interest, as they make it possible to carry out low-cost analyses on raw materials and finished products in a relatively short time. Indeed, immunoassays are based on the specific and selective antibody/antigen reaction, and they have been extensively applied for clinical diagnostic, alimentary quality control and environmental security purposes, and even for routine analysis. Since the complexity and variability of the matrices, as well as the great variety of compounds present in cosmetics, are analogous with those from food sources, immunological methods could also be applied successfully in this field. Indeed, this would provide a valid approach for the monitoring of industrial production chains even in developing countries, which are currently the greatest producers of cosmetics and the major exporters of raw materials. This review aims to highlight the immunological techniques proposed for cosmetics analysis, focusing on the detection of prohibited/regulated compounds, bacteria and toxins, and allergenic substances, and the identification of counterfeits.

Development and Efficacy of Lateral Flow Point-of-Care Testing Devices for Rapid and Mass COVID-19 Diagnosis by the Detections of SARS-CoV-2 Antigen and Anti-SARS-CoV-2 Antibodies

The COVID-19 pandemic is an ongoing global pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in 2020-2021. COVID-19 is becoming one of the most fatal pandemics in history and brings a huge challenge to the global healthcare system. Opportune detection, confinement, and early treatment of infected cases present the first step in combating COVID-19. Diagnosis via viral nucleic acid amplification tests (NAATs) is frequently employed and considered the standard procedure. However, with an increasing urge for point-of-care tests, rapid and cheaper immunoassays are widely utilized, such as lateral flow immunoassay (LFIA), which can be used for rapid, early, and large-scale detection of SARS-CoV-2 infection. In this narrative review, the principle and technique of LFIA applied in COVID-19 antigen and antibody detection are introduced. The diagnostic sensitivity and specificity of the commercial LFIA tests are outlined and compared. Generally, LFIA antigen tests for SARS-CoV-2 are less sensitive than viral NAATs, the "gold standard" for clinical COVID-19 diagnosis. However, antigen tests can be used for rapid and mass testing in high-risk congregate housing to quickly identify people with COVID-19, implementing infection prevention and control measures, thus preventing transmission. LFIA anti-SARS-CoV-2 antibody tests, IgM and/or IgG, known as serology tests, are used for identification if a person has previously been exposed to the virus or vaccine immunization. Notably, advanced techniques, such as LFT-based CRISPR-Cas9 and surface-enhanced Raman spectroscopy (SERS), have added new dimensions to the COVID-19 diagnosis and are also discussed in this review.

Development of a group-specific antibody-based immunoassay method for simultaneously detecting sildenafil-like adulterants in herbal spirit drinks

Phosphodiesterase type 5 (PDE-5) inhibitors are commonly used to treat erectile dysfunction. There is a problem with synthesis and illegal use of a wide range of analogues of the licenced drugs and a simple class-wide analytical method is required. In this work, based on structural modelling, we developed an immunological method using norneovardenafil as a hapten as it contains only the general sub-structure and the common features of sildenafil-like adulterants, such as hydrophobic centres, hydrogen-bond donor atoms and hydrogen-bond acceptor atoms. Thus theoretically it could induce production of antibody which could recognise multiple sildenafil-like adulterants. By immunising rabbits, a group-specific polyclonal antibody was obtained with the desired broad-spectrum molecular recognition performance against sildenafil-like adulterants. Then, an indirect competitive enzyme-linked immunosorbent assay (icELISA) was developed for the detection of sildenafil-like adulterants in herbal spirit drinks. Under the optimised conditions, the icELISA method showed broad linear ranges for acetildenafil, sildenafil and vardenafil respectively of 0.7 to 27.7 μg/kg, 1.0 to 70.7 μg/kg and 1.5 to 22.7 μg/kg, with half-maximal inhibition concentration (IC₅₀) values of 4.5 μg/kg, 8.3 μg/kg and 5.7 μg/kg, respectively. For eleven herbal spirit drinks, there was good agreement between total levels of sildenafil-like adulterants measured by icELISA and levels of each of four individual adulterants determined by LC-MS/MS. In short, the developed icELISA can be employed for rapid and simple screening for adulteration of herbal spirit drinks with sildenafil-like compounds.

Toxicant substitutes in immunological assays for mycotoxins detection: A mini review

Recurring mycotoxins contamination has posedaseriousthreatto food safety worldwide. Competitive immunoassays are widely used techniques for high-throughput mycotoxins detection in agricultural products and foods. However, the inevitable introduction of mycotoxin conjugates produced by chemical conjugation usually results in complicated by-products, large batch errors and threats to operators and environment. Biologically derived surrogates of mycotoxin conjugates or mycotoxin standards are renewable immunoreagents. They can serve the same function as the responding counterparts in the immunoassays. The substitute-based immunoassays exhibit satisfactory sensitivity, pose less health threats to operators and environment, and contribute to the standardization of immunoassays for mycotoxins. This review focuses on the current applications of substitute-based immunoassays, clarifies their underlying mechanisms and provides a careful comparison. Challenges and future prospects are discussed.

Application of phage-display developed antibody and antigen substitutes in immunoassays for small molecule contaminants analysis: A mini-review

Toxic small molecule contaminants (SMCs) residues in food threaten human health. Immunoassays are popular and simple techniques for SMCs analysis. However, immunoassays based on polyclonal antibodies, monoclonal antibodies and chemosynthetic antigens have some defects, such as complicated preparation of antibodies, risk of toxic haptens using for antigen chemosynthesis and so on. Phage-display technique has been proven to be an attractive alternative approach to producing antibody and antigen substitutes of SMCs, and opened up new realms for developing immunoassays of SMCs. These substitutes contain five types, including anti-idiotypic recombinant antibody (AIdA), anti-immune complex peptide (AIcP), anti-immune complex recombinant antibody (AIcA) and anti-SMC recombinant antibody (anti-SMC RAb). In this review, the principle of immunoassays based on the five types of substitutes, as well as their application and advantages are summarized and discussed.

Fluorescence immunoassay for multiplex detection of organophosphate pesticides in agro-products based on signal amplification of gold nanoparticles and oligonucleotides

Herein, we developed a multi-analyte fluorescence immunoassay for detection of three organophosphate pesticides (triazophos, parathion, and chlorpyrifos) in various agro-products (rice, wheat, cucumber, cabbage, and apple) using fluorescently labeled oligonucleotide and gold nanoparticle (AuNP) signal amplification technology. The AuNP probes for the three analytes were constructed by simultaneously modifying the corresponding antibodies and fluorescently labeled oligonucleotides on the probe surface. Three fluorophores (6-FAM, Cy3, and Texas red) with high fluorescence intensity and little overlap of excitation/emission wavelengths were selected. The method showed satisfactory linearity for triazophos, parathion, and chlorpyrifos in the ranges of 0.01-20, 0.05-50, and 0.5-1000 μg/L, respectively. For the 3 analytes, the limits of detection (LODs) were 0.007, 0.009, and 0.087 μg/L, respectively. The average recoveries were 77.7-113.6%, with relative standard deviations (RSDs) of 7.1-17.1% in various food matrices. The proposed method offers great potential in food safety surveillance, and could be used as well as a reference for multi-residue analysis of other small-molecule contaminants.

Design of Novel Haptens and Development of Monoclonal Antibody-Based Immunoassays for the Simultaneous Detection of Tylosin and Tilmicosin in Milk and Water Samples

In this work, a monoclonal antibody-based indirect competitive enzyme-linked immunosorbent assay (icELISA) was established to detect tylosin and tilmicosin in milk and water samples. A sensitive and specific monoclonal antibody was prepared by rational designed hapten, which was achieved by directly oxidizing the aldehyde group on the side chain of tylosin to the carboxyl group. Under the optimized conditions, the linear range of icELISA for tylosin and tilmicosin were 1.3 to 17.7 ng/mL and 2.0 to 47.4 ng/mL, with half-maximal inhibition concentration (IC₅₀) values of 4.7 and 9.6 ng/mL, respectively. The cross-reactivity with other analogues of icELISA was less than 0.1%. The average recoveries of icELISA for tylosin and tilmicosin ranged from 76.4% to 109.5% in milk and water samples. Besides, the detection results of icELISA showed good correlations with HPLC-MS/MS. The proposed icELISA was satisfied for rapid and specific screening of tylosin and tilmicosin residues in milk and water samples.

Development of a Simple Pretreatment Immunoassay Based on an Organic Solvent-Tolerant Nanobody for the Detection of Carbofuran in Vegetable and Fruit Samples

Nanobodies are one-tenth the size of conventional antibodies and are naturally obtained from the atypical heavy-chain-only antibodies present in camelids. Their small size, high solubility, high stability, and strong resilience to organic solvents facilitate their use as novel analytical reagents in immunochemistry. In this study, specific nanobodies against pesticide carbofuran were isolated and characterized from an immunized library via phage display platform. We further established an indirect competitive enzyme-linked immunosorbent assay (ELISA) using nanobody Nb316 to detect carbofuran in vegetable and fruit samples. The results showed a half-maximal inhibitory concentration (IC₅₀) of 7.27 ng/mL and a detection limit of 0.65 ng/mL. A simplified sample pretreatment procedure omitting the evaporation of organic solvent was used. The averaged recovery rate of spiked samples ranged between 82.3% and 103.9%, which correlated with that of standard UPLC–MS/MS method. In conclusion, a nanobody with high specificity for carbofuran was characterized, and a nanobody-based sensitive immunoassay for simple and rapid detection of carbofuran in real samples was validated.