Broadening the Detection Spectrum of Small Analytes Using a Two-Antibody-Designed Hybrid Immunoassay

Isolation of aptamers with excellent cross-reactivity and specificity to sulfonamides towards a ratiometric fluorescent aptasensor for the detection of nine sulfonamides in seafood

Sulfonamides (SAs) is a class of antibiotics that extensively used for treating infectious diseases in livestock industries and aquaculture. Thus, it is urgent need to obtain the bio-receptor, which has excellent cross-reactivity and specificity to SAs, for developing high-throughput methods for the determination of multiple SAs even all commonly-used SAs, to realize the quick screening/detection of total SAs in animal-derived foods. We herein isolated several SAs-specific cross-reactive aptamers by using a library-immobilized SELEX with multi-SAs parallel selection strategy. Two of the isolated aptamers (Sul-01 and Sul-04) can specifically recognize and bind seven SAs respectively with higher binding affinity and no interference of non-sulfonamide antibiotics, and thus can be applied as bio-receptors for developing high-throughput aptasensors for the quick screening/detection of multiple SAs. By using the mixture of Sul-01 and Sul-04 as bio-receptor, a ratiometric fluorescent aptasensor was created for the quick detection of nine SAs including sulfamethoxydiazine (SMD), sulfapyridine (SPD), sulfaquinoxaline (SQ), sulfathiazole (ST), sulfamonomethoxine (SMM), sulfamerazine (SMR), sulfaguanidine (SG), sulfamethazine (SMZ) and sulfadiazine (SD) with a detection limit (LOD) of 0.10-0.50 μM, or total of above nine SAs with a LOD of 0.20 μM. The fluorescent aptasensor was successfully applied to detect each or total of SMD, SPD, SQ, ST, SMM, SMR, SG, SMZ and SD in fish samples with a recovery of 83 %-92 % and a relative standard deviation (RSD, n = 5) < 5 %. This study not only provided several promising bio-receptors for the development of diverse high-throughput aptasensors to achieve the quick screening of multiple SAs residues, but also provided a simple, stable and sensitive method for the quick screening of SMD, SPD, SQ, ST, SMM, SMR, SG, SMZ and SD in seafood.

Copper complexes for the chemoselective N-arylation of arylamines and sulfanilamides via Chan-Evans-Lam cross-coupling

Copper(II) complexes with tridentate NNN-ligands were utilized for Chan-Evans-Lam (CEL) cross-coupling reactions to enable the N-arylation of multifarious N-nucleophiles through the activation of aryl boronic acids. A condition-specific methodology was developed to chemoselectively target the amine versus sulfonamide N-arylation of 4-aminobenzenesulfonamide using new catalysts. Two different pyridine-based ligands and corresponding copper(II) complexes were characterized using 1H and 13C-NMR, FTIR, and UV-vis spectroscopy, HRMS, single-crystal X-ray diffraction, and cyclic voltammetry. Solvent and base-controlled cross-coupling reactions were observed, which led to the optimization of selective conditions for targeted C-N bond formation of sulfanilamides. Beyond the chemoselective processes reported here, a breadth of N-nucleophiles including sulfanilamides and arylamines were screened for arylation by this CEL catalyst.

Immunotechniques for the Group Determination of Macrolide Antibiotics Traces in the Environment Using a Volume-Mediated Sensitivity Enhancement Strategy

Macrolide antibiotics, which are effective antimicrobial agents, are intensively used in human and veterinary medicine, as well as in agriculture. Consequently, they are found all over the world as environmental pollutants, causing harm to sensitive ecological communities and provoking a selection of resistant forms. A novel azithromycin derivative, which was used as hapten conjugate, ensured the group immunorecognition of six major macrolide representatives (105-41%), namely erythromycin, erythromycin ethylsuccinate, clarithromycin, roxithromycin, azithromycin, and dirithromycin in a competitive immunoassay based on anti-clarithromycin antibodies. The heterologous hapten-based ELISA format resulted in a 5-fold increase in sensitivity, with an IC50 value of 0.04 ng/mL for erythromycin. In this study, we proposed an underexploited strategy in an immunoassay field to significantly improve the detectability of analytes in environmental samples. Unlike most approaches, it does not require special enhancers/amplifiers or additional concentration/extraction procedures; instead, it involves analyzing a larger volume of test samples. A gradual volume increase in the samples (from 0.025 to 10 mL) analyzed using a direct competitive ELISA, immunobeads, and immunofiltration assay formats based on the same reagents resulted in a significant improvement (more than 50-fold) in assay sensitivity and detection limit up to 5 and 1 pg/mL, respectively. The suitability of the test for detecting the macrolide contamination of natural water was confirmed by the recovery of macrolides from spiked blank samples (71.7-141.3%). During 2022-2023, a series of natural water samples from Lake Onega and its influents near Petrozavodsk were analyzed, using both the developed immunoassay and HPLC-MS/MS. The results revealed no contamination of macrolide antibiotic.

Construction of a Highly Selective Enrichment, Ionization, and Detection Platform Based on a Broad-Spectrum Antibody

Ambient mass spectrometry (AMS) allows direct analysis of various raw food samples with minimal or no sample pretreatment, but the trace analytes in complex food samples still have problems with limitations. In this work, we developed a platform based on coated stainless steel sheet spray mass spectrometry for fast, in situ, high-throughput, and high selectivity multiresidue analysis of fluoroquinolone drugs (FQs). The sensitivity of the platform was enhanced via coupling broad-spectrum antibodies against FQs to graphene oxide coated blade spray (CBS)-MS through a streptavidin-biotin (SA-biotin) interaction. The prepared platform had sufficient loading capacity for SA (1.37 mg/piece) and the antibody (84.8 μg/piece), which is greater than that of physical mixing and the EDC/NHS covalent coupling strategy. With simplified sample pretreatment, this platform demonstrated comparable sensitivity to high performance liquid chromatography-mass spectrometry (HPLC-MS/MS) (0.08-0.16 ng/mL in phosphate-buffered saline and 0.21-0.32 ng/mL in diluted milk). Meanwhile, compared with HPLC-MS/MS, the method is rapid (enrichment: 10 min, detection: <1 min) and acceptable recoveries (81.94-102.08%) can be obtained. The presence of analytes can be monitored by MS/MS spectra, and multiple analytes can be measured simultaneously in a single assay. This study is expected to provide a powerful and portable tool for rapid laboratory analysis and reliable screening in the field.

A multicolor immunosensor for the visual detection of six sulfonamides based on manganese dioxide nanosheet-mediated etching of gold nanobipyramids

In reality, various sulfonamides (SAs) were alternately used in animal husbandry to avoid generating drug resistance. Thus, it is crucial to develop simple and high-throughput methods for detecting multiple or groups of SAs to realize rapid screening of total SAs residues in foods. We herein developed a sensitive and efficient MnO₂ nanosheets-mediated etching of gold nanobipyramids (AuNBPs), which can generate more vivid color changes, and further fabricated a high-throughput multicolor immunosensor for the visual screening/semi-quantitative detection of 6 different SAs including sulfamethazine (SMZ), sulfamethoxydiazine (SMD), sulfisomidine (SIM), sulfamerazine (SMR), sulfamonomethoxine (SMM) and sulfaquinoxaline (SQ) by using AuNBPs as signal and broad-specificity anti-SAs antibody as a bio-receptor. The immunosensor displays more vivid color changes, and has a lower visual detection limit and excellent specificity. It can be applied to detect as little as 1.0 ng/mL of SMZ, SMD, SMR and 2.0 ng/mL of SIM, SMM, SQ by bare eye observation, and 0.2 ng/mL of above 6 SAs by UV-visible spectrophotometry. The visual detection limit of the immunosensor is much lower than the maximum residue limit of total SAs (100 μg/kg) in edible tissues. The immunosensor was successfully applied to detect SMZ, SMD, SIM, SMR, SMM and SQ in milk with a recovery of 84%-106% and a RSD (n = 5) < 8%. The success of this study provided a promising assay for the on-site rapid screening of SMZ, SMD, SIM, SMR, SMM and SQ in food by bare eye observation. Importantly, the immunosensor may be expended as a general method for the visual screening/semi-quantitative detection of the group of other antibiotics by using the corresponding broad-specificity antibody as a bio-receptor.

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.

Broad-Specificity Aptamer of Sulfonamides: Isolation and Its Application in Simultaneous Detection of Multiple Sulfonamides in Fish Sample

Sulfonamide antibiotics (SAs) are widely used in animal husbandry and aquaculture, and the excess residues of SAs in animal-derived foods will harm the health of consumers. In reality, various SAs were alternately used in animal husbandry and aquaculture, and thus, it is urgent need to develop simple and high-throughput methods for simultaneously detecting multiple SAs or groups of SAs in order to realize rapid screening of total SAs residues in animal-derived foods. We herein isolated a broad-specificity aptamer for SAs by using a multi-SAs systematic evolution of ligands by exponential enrichment (SELEX) strategy. The isolated broad-specificity aptamer has a higher binding affinity to five different SAs including sulfaquinoxaline (SQ), sulfamethoxypyridazine (SMPZ), sulfametoxydiazine (SMD), sulfachloropyridazine (SCP), and sulfapyridine (SPD) and, thus, can be used as a bioreceptor for developing various high-throughput methods for the simultaneous detection or rapid screening of above five SAs. Based on the isolated broad-specificity aptamer and Cy7 (diethylthiatricarbocyanine) displacement strategy, a colorimetric aptasensor was developed for the simultaneous detection of SQ, SMPZ, SMD, SCP, and SPD with a visual detection limit of 2.0-5.0 μM and a spectrometry detection limit of 0.2-0.5 μM. The colorimetric aptasensor was successfully used to detect SQ, SMPZ, SMD, SCP, and SPD in fish muscle with a recovery of 82%-92% and a RSD (n = 5) < 7%. The success of this study provided a promising bioreceptor for developing various high-throughput methods for on-site rapid screening of multiple SAs residues, as well as a simple method for the rapid and cost-effective screening of total SQ, SMPZ, SMD, SCP, and SPD in seafood.

Immunoanalytical methods for ochratoxin A monitoring in wine and must based on innovative immunoreagents

Immunochemical methods are highly deployed in analytical laboratories worldwide for monitoring the incidence of mycotoxins in the food chain. Nevertheless, most conventional immunoassays for ochratoxin A (OTA), including commercial kits, show limitations to robustly determine this mycotoxin in grape-derived products below regulated levels (2 ng/mL). Herein, two rapid tests for sensitive OTA determination in wine and must were developed capitalizing on a collection of bioconjugates from innovative synthetic haptens and monoclonal antibodies with subnanomolar affinity. The ELISA (LOD = 8 pg/mL) showed excellent performance in recovery studies, and it was applied to survey commercial wines and musts for OTA contamination. Concerning LFIA, validation according to the Commission Regulation 519/2014 showed that samples exceeding 2 ng/mL were properly scored as uncompliant. More importantly, illegal samples provided a complete inhibition of the test signal, making this test an easy-to-use, rapid, and convenient screening method for in-house control of OTA in wineries.

Rapid Multi-Residue Detection Methods for Pesticides and Veterinary Drugs

The excessive use or abuse of pesticides and veterinary drugs leads to residues in food, which can threaten human health. Therefore, there is an extremely urgent need for multi-analyte analysis techniques for the detection of pesticide and veterinary drug residues, which can be applied as screening techniques for food safety monitoring and detection. Recent developments related to rapid multi-residue detection methods for pesticide and veterinary drug residues are reviewed herein. Methods based on different recognition elements or the inherent characteristics of pesticides and veterinary drugs are described in detail. The preparation and application of three broadly specific recognition elements-antibodies, aptamers, and molecular imprinted polymers-are summarized. Furthermore, enzymatic inhibition-based sensors, near-infrared spectroscopy, and SERS spectroscopy based on the inherent characteristics are also discussed. The aim of this review is to provide a useful reference for the further development of rapid multi-analyte analysis of pesticide and veterinary drug residues.

Production of generic monoclonal antibody and development of chemiluminescence immunoassay for determination of 32 sulfonamides in chicken muscle

A hapten of sulfabenzamide was first synthesized to generate a monoclonal antibody that simultaneously recognized 32 sulfonamides. The computational simulation showed that the 3D conformation, molecular bend angle, molecular volume, electronic charge of core structure of these drugs all showed influences on the antibody binding. The antibody was combined with a heterologous enzyme-labeled hapten to develop a direct competitive chemiluminescence enzyme linked immunosorbent assay for determination of the 32 sulfonamides in chicken muscle sample. The CRs of the optimized method for these drugs were in the range of 7.3%-1778%, and the IC₅₀ values were in the range of 0.038-11.2 ng/g. The limits of detection for detection of these drugs in chicken were in the range of 0.03-26 ng/g. Their recoveries from the standards fortified blank chicken samples were in the range of 60.8%-97.1%. Therefore, this method could be used as a useful tool for routine screening sulfonamides residues in meat.

Faraday-Cage-Type Electrochemiluminescence Immunoassay: A Rise of Advanced Biosensing Strategy

Electrochemiluminescence immunoassays are usually carried out through "on-electrode" strategy, i.e., sandwich-type immunoassay format, the sensitivity of which is restricted by two key bottlenecks: (1) the number of signal labels is limited and (2) only a part of signal labels could participate in the electrode reaction. In this Perspective, we discuss the development of an "in-electrode" Faraday-cage-type concept-based immunocomplex immobilization strategy. The biggest difference from the traditional sandwich-type one is that the designed "in-electrode" Faraday-cage-type immunoassay uses a conductive two-dimensional (2-D) nanomaterial simultaneously coated with signal labels and a recognition component as the detection unit, which could directly overlap on the electrode surface. In such a case, electrons could flow freely from the electrode to the detection unit, the outer Helmholtz plane (OHP) of the electrode is extended, and thousands of signal labels coated on the 2-D nanomaterial are all electrochemically "effective." Thus, then, the above-mentioned bottlenecks obstructing the improvement of the sensitivity in sandwich-type immunoassay are eliminated, and as a result a much higher sensitivity of the Faraday-cage-type immunoassay can be obtained. And, the applications of the proposed versatile "in-electrode" Faraday-cage-type immunoassay have been explored in the detection of target polypeptide, protein, pathogen, and microRNA, with the detection sensitivity improved tens to hundreds of times. Finally, the outlook and challenges in the field are summarized. The rise of Faraday-cage-type electrochemiluminescence immunoassay (FCT-ECLIA)-based biosensing strategies opens new horizons for a wide range of early clinical identification and diagnostic applications.

Optical Fiber-Mediated Immunosensor with a Tunable Detection Range for Multiplexed Analysis of Veterinary Drug Residues

We describe herein a newly developed chemiluminescent optical fiber immunosensor (OFIS) with a tunable detection range for multiplexed analysis of veterinary drug residues with vastly different concentrations in milk samples. The optical fiber probe is used as a carrier of biorecognition element as well as a transducer, enabling a low-cost compact design, which makes this system suitable for cost-effective on-site detection of the target analytes. Importantly, the synergy between modulation of the length of the optical fiber sensing region and the number of fibers allows performing multiplexed immunoassays in an easily controllable manner over a tunable detection range from pg/mL to μg/mL analyte concentrations. By combining the optical fiber sensor with a nanocomplex signal amplification system, a highly sensitive chemiluminescent OFIS system is demonstrated for the multiplexed assaying of veterinary drug residues in milk samples with linear ranges of 10-(2 × 10⁴) pg/mL for chloramphenicol, 0.5-500 ng/mL for sulfadiazine, and 0.1-300 μg/mL for neomycin. This controllable strategy, based on modulation of the fiber probe, provides a versatile platform for multiplexed quantitative detection of both low-abundance and high-abundance targets, which shows great potential for on-site testing in food safety.

Sensitive and multiplexed detection of antibiotics using a suspension array platform based on silica-agarose hybrid microbeads

A multiplex suspension array detection platform of antibiotics has been developed based on silica-agarose hybrid microbeads (SAHMs). Chloramphenicol (CAP), sulfamethoxazole (SMX), metronidazole (MTZ) and amoxicillin (AMX) were employed as model analytes. The antigens (the antibiotics conjugated with BSA) were immobilized on the surface of four different types of SAHMs. Based on an indirect competition immunoassay, the selected antibiotics are detected through the competition of the specific monoclonal antibodies between the multiple antibiotics and the antigens. Due to high resistance to nonspecific protein absorption of SAHMs, the proposed method exhibited wide linear ranges (0.4˜72.9 ng/mL for CAP, 2.0˜108.5 ng/mL for SMX, 2.6˜142.2 ng/mL for MTZ, 1.0˜63.3 ng/mL for AMX) and low detection limits of 0.09˜0.8 ng/mL. Recoveries for spiked tap water samples were from 82% to 113%, with relative standard deviation lower than 14%, demonstrating the accuracy of the measurements performed with the developed method. This work offered a high-throughput, flexible and accurate tool, which provides a good platform for simultaneous detection of antibiotics.

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.

Novel haptens and monoclonal antibodies with subnanomolar affinity for a classical analytical target, ochratoxin A

Ochratoxin A is a potent toxic fungal metabolite whose undesirable presence in food commodities constitutes a problem of public health, so it is strictly regulated and controlled. For the first time, two derivatives of ochratoxin A (OTAb and OTAd) functionalized through positions other than the native carboxyl group of the mycotoxin, have been synthesized in order to better mimic, during the immunization process, the steric and conformational properties of the target analyte. Additionally, two conventional haptens making use of that native carboxyl group for protein coupling (OTAe and OTAf) were also prepared as controls for the purpose of comparison. The immunological performance in rabbits of protein conjugates based on OTAb and OTAd overcome that of conjugates employing OTAe and OTAf as haptens. After immunization of mice with OTAb and OTAd conjugates, a collection of high-affinity monoclonal antibodies to ochratoxin A was generated. In particular, one of those antibodies, the so-called OTAb#311, is very likely the best antibody produced so far in terms of selectivity and affinity to ochratoxin A.