Development of competitive and noncompetitive immunoassays for clothianidin with high sensitivity and specificity using phage-displayed peptides

Enzyme- and label-free cascade isothermal amplification aptasensor for the ultrasensitive detection of ochratoxin A

BACKGROUND

Ultrasensitive detection is crucial for the early warning and intervention of risk factors, ultimately benefiting the environment and human health. Low levels of ochratoxin A (OTA) present a hidden yet significant threat, and rapid detection via high-performing biosensors is therefore essential.

RESULTS

A cascade isothermal amplification aptasensor (CIA-aptasensor) was designed for OTA detection. On the surface of a magnetic bead probe, the OTA level was converted into positively correlated trigger cDNA through its competitive binding with OTA-Apt. The released trigger cDNA activated catalytic hairpin assembly followed by coupling with a hybridization chain reaction to achieve CIA. After adding graphene oxide and SYBR Green I, the background interference was eliminated to specifically obtain OTA-related fluorescence. The ultrasensitive limit of detection was 0.22 pg mL-1, an improvement of 1368-fold over conventional enzyme-linked aptamer sorbent assay by the same OTA-Apt, demonstrating satisfactory reliability and practicability. Thus, the CIA-aptasensor provides an enzyme- and label-free simplified homogeneous system with minimal background interference using isothermal conditions.

SIGNIFICANCE

This study provides a polymerase chain reaction-like approach for enhancing the sensitivity and performance of a biosensor, which could be extended for the application of CIA and label-free signaling strategy to other risk factors.

Plasmonic colorimetry and G-quadruplex fluorescence-based aptasensor: A dual-mode, protein-free and label-free detection for OTA

G-quadruplexes (G4) have received significant attention in the field of aptasensors owing to their unique physicochemical characteristics. A dual-mode, protein-free and label-free aptamer sensor based on plasmonic colorimetry and G4 fluorescence (PC@GF-aptasensor) was proposed for ochratoxin A (OTA). Colorimetry mode was achieved through the surface plasmon resonance (SPR) effect, which related to the OTA-Apt-based G4-OTA. The fluorescence mode was reflected by the insertion of thioflavin T (ThT) into G4-OTA. The OTA could be interpreted via three readouts: (1) naked eye (LOD of 2.0 ng mL-1), (2) smartphone (LOD of 1.65 ng mL-1), and (3) spectrofluorometer (LOD of 0.93 ng mL-1). The PC@GF-aptasensor exhibited several advantages, such as a standardised recognition group, simplified operation, low background signal, and practicality. The proposed PC@GF-aptasensor integrated SPR-based multicolour interpretation and ThT-inserted fluorescence reflection to obtain a dual-mode optical biosensor, which may provide valuable insights for the development of other targets with G4-based aptamers.

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.

Residue Behaviors and Degradation Dynamics of Insecticides Commonly Applied to Agrocybe aegerita Mushrooms from Field to Product Processing and Corresponding Risk Assessments

Residual pesticides in Agrocybe aegerita mushroom have emerged as a significant concern and bring much uncertainty due to processing procedures. In this study, a modified QuEChERS sample preparation procedure and UPLC-MS/MS were used to analyze the residual levels of four commonly used pesticides in A. aegerita from field to product processing. The field results showed that dissipation of these targeted chemicals was consistent with the first-order kinetics, and the half-life time ranged from 20.4 h to 47.6 h. The terminal residues of the four pesticides at harvest time ranged from 9.81 to 4412.56 μg/kg in raw mushroom. The processing factors (PFs) of clothianidin, diflubenzuron, chlorbenzuron, and pyridaben ranged from 0.119 to 0.808 for the drying process and from 0.191 to 1 for the washing process. By integrating the data from the field trials, the PFs, and the consumption survey, the chronic dietary risks of the target chemicals via A. aegerita intake ranged from 2.41 × 10-5 to 5.69 × 10-2 for children and from 6.34 × 10-6 to 1.88 × 10-2 for adults, which are considerably below the threshold of 1, indicating no unacceptable risk to consumers in the Fujian province of China. This research offers foundational data for appropriate use and the maximum residue limit (MRL) establishment for these four insecticides in A. aegerita.

Heterologous antigen selection of chicken single-chain variable fragments against thiamethoxam

Single-chain variable fragments (scFvs) are valuable in the development of immunoassays for pesticide detection. In this study, scFvs specific to thiamethoxam (Thi) were successfully isolated from a library generated by chicken immunization through heterologous coating selection. These scFvs were subsequently expressed with fusion with an Avi tag and alkaline phosphatase. After combination and optimization, a scFv-biotin based enzyme linked immunosorbent assay (ELISA) was developed for the detection of Thi, demonstrating an impressive half-maximum signal inhibition concentration (IC50) of 30 ng mL-1 and a limit of detection (LOD) of 1.8 ng mL-1. The immunoassay exhibited minimal cross-reactivity with other neonicotinoid insecticides, except for 7.5% for imidacloprid and 6.7% for imidaclothiz. The accuracy of the assay was confirmed by testing spiked samples of apple, pear, cabbage, and cucumber, which resulted in average recoveries ranging between 82% and 119%, closely aligning with the results obtained through high-performance liquid chromatography. Therefore, the chicken scFv-biotin based assay showed promise as a high-throughput screening tool for Thi in agricultural samples.

Inner filter effect-based upconversion nanosensor for rapid detection of thiram pesticides using upconversion nanoparticles and dithizone-cadmium complexes

Herein, we propose a method for detecting thiram based on the fluorescence inner filter effect using upconversion nanoparticles and dithizone-cadmium complexes (DZ-Cd2+). The ultraviolet absorption of DZ-Cd2+ was in the range of 480-600 nm under alkaline conditions, resulting in fluorescence quenching of the nanoparticles at 540 nm. Thiram had a stronger coordination effect with Cd2+ than dithizone; thus, more thiram-cadmium complex (T-Cd2+) formed when thiram was added, leading to fluorescence recovery at 540 nm. The standard thiram curve was found to have a detection limit of 6.75 ng/mL in the linear range of 0.01-1000 µg/mL. In addition, high-performance liquid chromatography results for detecting thiram in apple samples revealed good application performance. The results demonstrate that the developed method has great potential to detect thiram residues in food.

Development of competitive and noncompetitive lateral flow immunoassays for pendimethalin using synthetic peptides

Peptidomimetic and anti-immunocomplex peptides can be easily isolated from phage display libraries, and can be used as alternatives to chemical competing haptens to improve the sensitivity of small molecule immunoassay. In this work, 16 peptidomimetics and 7 anti-immunocomplex peptides of pendimethalin (PND) were obtained from cyclic 7-, 8-, 9-, and 10-residue peptide phage libraries. Peptidomimetic EJ-2 (CMFTGTDFPC) with the highest sensitivity in competitive phage enzyme-linked immunosorbent assay (ELISA) and immunocomplex peptide EF-30 (CNPGWPPIPC) with the highest sensitivity in noncompetitive phage ELISA were selected to prepare phage-free peptides with GGGSSK-biotin at the C-terminus. Competitive and noncompetitive lateral flow immunoassays (CLFIA and NLFIA) were developed by using the phage-free peptides. After optimization, the CLFIA and NLFIA showed visual limit of detections (vLODs) of 5 ng/mL and 2.5 ng/mL, respectively, which were improved two- and fourfold compared with a LFIA based on chemical hapten. The NLFIA showed better sensitivity than CLFIA in the detection of spiked samples, and can meet the detection requirements for agro-products regulated by EU and China. The detection results of CLFIA and NLFIA for blind samples were consistent with that of ultra performance liquid chromatography/tandem mass spectrometry.

Combination of nanobody and peptidomimetic to develop novel immunoassay platforms for detecting ochratoxin A in cereals

Mimotope-based immunoassays for mycotoxins eliminate the requirement for large amounts of mycotoxin standards for the chemosynthesis of artificial antigens. Herein, the nanobody-based magnetic beads were used to screen the mimotope (peptidomimetic) of ochratoxin A (OTA) from the phage-displayed peptide library. The interactions between nanobody and the most sensitive Y4 peptidomimetic were investigated by computer-assisted simulation and compared with those between nanobody and OTA. By combining the nanobody, the phage-displayed Y4 and alkaline phosphatase-tagged Y4 fusion protein as the competing antigens, were used to develop two novel immunoassay platforms (PN-ELISA and APN-ELISA). The two methods are advantageous in the use of nontoxic substitutes of OTA and avoiding the use of monoclonal antibodies. Moreover, good analytical performances of both methods were obtained and confirmed by liquid chromatography tandem mass spectrometry. Therefore, the proposed novel methods based on nanobody and peptidomimetic were demonstrated to be highly reliable for detecting OTA in food.

M13 Bacteriophage-Assisted Recognition and Signal Spatiotemporal Separation Enabling Ultrasensitive Light Scattering Immunoassay

The demand for the ultrasensitive and rapid quantitative analysis of trace target analytes has become increasingly urgent. However, the sensitivity of traditional immunoassay-based detection methods is limited due to the contradiction between molecular recognition and signal amplification caused by the size effect of nanoprobes. To address this dilemma, we describe versatile M13 phage-assisted immunorecognition and signal transduction spatiotemporal separation that enable ultrasensitive light-scattering immunoassay systems for the quantitative detection of low-abundance target analytes. The newly developed immunoassay strategy combines the M13 phage-assisted light scattering signal fluctuations of gold nanoparticles (AuNPs) with gold in situ growth (GISG) technology. Given the synergy of M13 phage-mediated leverage effect and GISG-amplified light scattering signal modulation, the practical detection capability of this strategy can achieve the ultrasensitive and rapid quantification of ochratoxin A and alpha-fetoprotein in real samples at the subfemtomolar level within 50 min, displaying about 4 orders of magnitude enhancement in sensitivity compared with traditional phage-based ELISA. To further improve the sensitivity of our immunoassay, the biotin-streptavidin amplification scheme is implemented to detect severe acute respiratory syndrome coronavirus 2 spike protein down to the attomolar range. Overall, this study offers a direction for ultrasensitive quantitative detection of target analytes by the synergistic combination of M13 phage-mediated leverage effect and GISG-amplified light scattering signal modulation.

Plasmonic colorimetric immunosensor based on Poly-HRP and AuNS etching for tri-modal readout of small molecule

It was urgent to improve the intuitive, portable, sensitive and multi-modal detection method for small molecules. In this study, a tri-modal readout of plasmonic colorimetric immunosensor (PCIS) for small molecule (zearalenone, ZEN, as an example) had been established based on the Poly-HRP amplification and gold nanostars (AuNS) etching. The immobilized Poly-HRP from the competitive immunoassay was used to catalyze iodide (I^-) into iodine (I₂), which could prevent the AuNS etching by I^-. With the increasing of ZEN, the AuNS etching was enhanced, and the localized surface plasmon resonance (LSPR) peak of AuNS showed stronger blue shift, which resulted in the color changing from deep blue (no-etching) to blue violet (half-etching) and finally to shiny red (all-etching). The results of PCIS could be selectively obtained by the tri-modal readout: (1) naked eye (LOD of 0.10 ng/mL), (2) smartphone (LOD of 0.07 ng/mL) and (3) UV-spectrum (LOD of 0.04 ng/mL). The proposed PCIS had performed well in the sensitivity, specificity, accuracy and reliability. In addition, the harmless reagents were used in the overall process to further guarantee the environmental friendliness. Therefore, the PCIS might provide a novel and green avenue for the tri-modal readout of ZEN via the intuitive naked eye, portable smartphone and accurate UV-spectrum, which hold great potential for small molecule monitoring.

Antibody-free and selective detection of okadaic acid using an affinity peptide-based indirect assay

Okadaic acid (OA) is a type of marine biotoxin produced by some species of dinoflagellates in marine environments. Consumption of shellfish contaminated with OA can cause diarrhetic shellfish poisoning (DSP) in humans with symptoms that typically include abdominal pain, diarrhea and vomiting. In this study, we developed an affinity peptide-based direct competition enzyme-linked immunosorbent assay (dc-ELISA) for the detection of OA in real samples. The OA-specific peptide was successfully identified via M13 biopanning and a series of peptides were chemically synthesized and characterized their recognition activities. The dc-ELISA system showed good sensitivity and selectivity with a half-maximal inhibitory concentration (IC₅₀) of 148.7 ng/mL and a limit of detection (LOD) of 5.41 ng/mL (equivalent, 21.52 ng/g). Moreover, the effectiveness of the developed dc-ELISA was validated using OA-spiked shellfish samples, and the developed dc-ELISA showed a high recovery rate. These results suggest that the affinity peptide-based dc-ELISA can be a promising tool for detecting OA in shellfish samples.

Broad-specificity monoclonal antibody against neonicotinoid insecticides via a multi-immunogen strategy and development of a highly sensitive GNP-based multi-residue immunoassay in ginseng and tomato

Neonicotinoid insecticides (NNIs) are extensively used across the agricultural products and foods. In order to meet the rapid detection requirements, a novel broad-specificity monoclonal antibody against NNIs was developed for the first time using a multi-immunogen strategy. The antibody's high affinity and its ability to bind target molecules were verified by ic-ELISA. Furthermore, molecular docking was used to evaluate the pivotal forces affecting binding affinity and to determine binding sites. Subsequently, a highly sensitive gold nanoparticle-based immunochromatographic assay was established for the rapid detection of eight NNIs and the IC₅₀ values were 0.03-1.61 ng/mL. The limits of detection for ginseng and tomato ranged from 0.76 to 30.19 μg/kg and 0.87 to 31.57 μg/kg, respectively. The spiked recovery ranged from 72.04% to 120.74%, and the coefficient of variation were less than 9.0%. This study provides a new direction for the development of multiple NNIs residue immunoassays.

M13 phage: a versatile building block for a highly specific analysis platform

Viruses are changing the biosensing and biomedicine landscape due to their multivalency, orthogonal reactivities, and responsiveness to genetic modifications. As the most extensively studied phage model for constructing a phage display library, M13 phage has received much research attention as building blocks or viral scaffolds for various applications including isolation/separation, sensing/probing, and in vivo imaging. Through genetic engineering and chemical modification, M13 phages can be functionalized into a multifunctional analysis platform with various functional regions conducting their functionality without mutual disturbance. Its unique filamentous morphology and flexibility also promoted the analytical performance in terms of target affinity and signal amplification. In this review, we mainly focused on the application of M13 phage in the analytical field and the benefit it brings. We also introduced several genetic engineering and chemical modification approaches for endowing M13 with various functionalities, and summarized some representative applications using M13 phages to construct isolation sorbents, biosensors, cell imaging probes, and immunoassays. Finally, current issues and challenges remaining in this field were discussed and future perspectives were also proposed.

Development of Ic-ELISA and Colloidal Gold Lateral Flow Immunoassay for the Determination of Cypermethrin in Agricultural Samples

Cypermethrin (CYP) is an insecticide in the pyrethroid family and is used widely in agriculture and for public health purposes. However, CYP has been shown to have negative impacts on reproduction, immunity and nerves in mammals. In this study, a monoclonal antibody (mAb) against CYP was prepared and used to establish an indirect competitive immunosorbent assay (ic-ELISA) and colloidal gold lateral flow immunoassay (LFIA) for the quantitative and qualitative determination of CYP residues in agricultural products. The half inhibition concentration of the ic-ELISA was 2.49 ng/mL, and the cut-off value and visual limit of detection of the LFIA were 0.6 and 0.3 μg/mL, respectively. The recovery rates of the ic-ELISA ranged from 78.8% to 87.6% in tomato, cabbage and romaine lettuce. The qualitative results of LFIA and quantitative results of ic-ELISA and HPLC were in good agreement in blind samples. Overall, the established ic-ELISA and LFIA proved to be accurate and rapid methods for the determination of CYP in agricultural products.

Small Peptides in the Detection of Mycotoxins and Their Potential Applications in Mycotoxin Removal

Mycotoxins pose significant risks to humans and livestock. In addition, contaminated food- and feedstuffs can only be discarded, leading to increased economic losses and potential ecological pollution. Mycotoxin removal and real-time toxin level monitoring are effective approaches to solve this problem. As a hot research hotspot, small peptides derived from phage display peptide libraries, combinatorial peptide libraries, and rational design approaches can act as coating antigens, competitive antigens, and anti-immune complexes in immunoassays for the detection of mycotoxins. Furthermore, as a potential approach to mycotoxin degradation, small peptides can mimic the natural enzyme catalytic site to construct artificial enzymes containing oxidoreductases, hydrolase, and lyase activities. In summary, with the advantages of mature synthesis protocols, diverse structures, and excellent biocompatibility, also sharing their chemical structure with natural proteins, small peptides are widely used for mycotoxin detection and artificial enzyme construction, which have promising applications in mycotoxin degradation. This paper mainly reviews the advances of small peptides in the detection of mycotoxins, the construction of peptide-based artificial enzymes, and their potential applications in mycotoxin control.

Identification and Application of Two Promising Peptide Ligands for the Immunodetection of Imidacloprid Residue

As the most widely used neonicotinoid insecticide, it is of great significance to explore the immunoreagents and immunoassays for imidacloprid (IMI) residue. In immunoassays, specific peptide ligands, such as peptidomimetic and anti-immunocomplex peptides, are regarded as promising substitutes for chemical haptens. In the present work, we identified thirty sequences of peptidomimetics and two sequences of anti-immunocomplex peptides for IMI from three phage pVIII display cyclic peptide libraries, in which the anti-immunocomplex peptides are the first reported noncompetitive reagents for IMI. The peptidomimetic 1-9-H and anti-immunocomplex peptide 2-1-H that showed the best sensitivity were utilized to develop competitive and noncompetitive phage enzyme-linked immunosorbent assays (P-ELISAs), with a half inhibition concentration of 0.55 ng/mL for competitive P-ELISA and a half-saturation concentration of 0.35 ng/mL for noncompetitive P-ELISA. The anti-immunocomplex peptide was demonstrated to greatly improve the specificity compared with competitive P-ELISA. In addition, the accuracy of proposed P-ELISAs was confirmed by recovery analysis and HPLC verification in agricultural and environmental samples. These results show that the peptide ligands identified from phage display library can replace chemical haptens in the immunoassays of IMI with the satisfactory performance.