Development of a Double Nanobody-Based Sandwich Immunoassay for the Detecting Staphylococcal Enterotoxin C in Dairy Products

Structural Insights Into the Mechanisms of Recognition of Recombinant Full-Length Antibodies for the Detection of Staphylococcus aureus Enterotoxins C1, C2, and C3

Food poisoning caused by Staphylococcus aureus (S. aureus) and its enterotoxins has become a global food safety issue. Herein, three types of Staphylococcal enterotoxins (SE), including SEC1, SEC2, and SEC3, were successfully expressed and immunized in mice to prepare monoclonal antibodies (mAbs). We screened a pair of mAbs 16E12-9B7 from 12 strains that could simultaneously recognize SEC1, SEC2, and SEC3. Furthermore, the genes from hybridoma cells 9B7 and 16E12 were extracted, amplified, and inserted into expression vectors to obtain recombinant antibodies (rAbs), whose affinities were consistent with those of ascites antibodies. The paired rAbs 16E12-9B7 were applied to a gold immunochromatographic strip (GICS) system to enable the rapid detection of SEC1, SEC2, and SEC3 with visual limits of detection (vLOD) of 2, 0.5, and 2 ng/mL in milk samples. Noticeably, we found that hydrogen bonds and salt bridges played a significant role in these antigen-antibody interactions. The key sites for 9B7 were ASN28 and SER31 in complementarity determining region (CDR) and the key sites for 16E12 were SER32 in the 16E12 variable light chain (VL) and ARG100, SER101, and TYR102 in the 16E12 variable heavy chain (VH). The analysis of key rAbs sites has potential in the screening of mutant antibodies.

High sensitivity chemiluminescence enzyme immunoassay for detecting staphylococcal enterotoxin C1 and its application in multi-matrices

Staphylococcal enterotoxins (SEs) serve as the primary cause of staphylococcal food poisoning and other foodborne intoxications. Among them, staphylococcal enterotoxin C (SEC) has the highest prevalence in dairy products, leading to multiple outbreaks all around the world. Thus, it is of great significance to develop a highly sensitive, highly specific and easy to operate chemiluminescent sandwich enzyme immunoassay (CLEIA) for detecting staphylococcal enterotoxin C (SEC1). We selected two pairs of anti-SEC1 monoclonal antibodies (mAbs) (SEC1-G8 and SEC1-C4), and a chemiluminescent sandwich enzyme immunoassay (CLEIA) was constructed. This approach can detect SEC1 within a concentration spectrum of 3.2-4000 pg/mL, with the detection limit being 2.1 pg/mL. At three concentrations (3.2, 20, and 400 pg/mL), both the intra- and inter-assay coefficient variations were coming in at 6.31 % and 11.2 % respectively. No cross-reaction was noticed in the SEA, SEB, and SED tests. SEC1 was successfully detected by employing the CLEIA method in spiked matrices and commercial samples, and the average recovery rate ranges from 81.6 % to 108.1 %. Therefore, the highly sensitive, SEC1- specific, and easy-to-operate CLEIA could be a useful tool in the near future for quantifying SEC1 in public health and food safety.

Food-Borne Biotoxin Neutralization in Vivo by Nanobodies: Current Status and Prospects

Food-borne biotoxins from microbes, plants, or animals contaminate unclean, spoiled, and rotten foods, posing significant health risks. Neutralizing such toxins is vital for human health, especially after food poisoning. Nanobodies (Nbs), a type of single-domain antibodies derived from the genetic cloning of a variable domain of heavy chain antibodies (VHHs) in camels, offer unique advantages in toxin neutralization. Their small size, high stability, and precise binding enable effective neutralization. The use of Nbs in neutralizing food-borne biotoxins offers numerous benefits, and their genetic malleability allows tailored optimization for diverse toxins. As nanotechnology continues to evolve and improve, Nbs are poised to become increasingly efficient and safer tools for toxin neutralization, playing a pivotal role in safeguarding human health and environmental safety. This review not only highlights the efficacy of these agents in neutralizing toxins but also proposes innovative solutions to address their current challenges. It lays a solid foundation for their further development in this crucial field and propels their commercial application, thereby contributing significantly to advancements in this domain.

Sea hedgehog-inspired surface-enhanced Raman scattering biosensor probe for ultrasensitive determination of Staphylococcus aureus in food supplements

Staphylococcus aureus contamination in food supplements poses substantial challenges to public health and large-scale production but the sensitive detection in a timely manner remains a bottleneck. Drawing inspiration from the sea hedgehog, gold nanostars (AuNSs) were leveraged to design an ultrasensitive surface-enhanced Raman scattering (SERS) biosensor for the determination of Staphylococcus aureus in food supplements. Besides the surface enhancement furnished by the AuNSs, Raman reporter molecules and specific aptamers sequentially self-assembled onto these AuNSs to construct the "three-in-one" SERS biosensor probe for label-based quantitation of Staphylococcus aureus. Following incubation with contaminated health product samples, the gold nanostars@Raman reporter-aptamer specifically recognize and assemble around Staphylococcus aureus cells, forming a distinctive sea hedgehog structure. This unique configuration results in an amplified Raman signal at 1338 cm-1 and an enhancement factor of up to 6.71 × 107. The entire quantitative detection process can be completed within 30 min, boasting an exceptional limit of detection as low as 1.0 CFU mL-1. The method exhibits a broad working range for the determination of Staphylococcus aureus, with concentrations spanning 2.15 CFU mL-1 to 2.15 × 105 CFU mL-1. Furthermore, it demonstrates outstanding precision, with relative standard deviation values consistently below 5.0%. As a showcase to validate the practicality of the SERS method, we conducted tests on determining Staphylococcus aureus in a herbal food supplement, i.e., Ginkgo Biloba extract (GBE); the results align closely with those obtained through the conventional lysogeny broth agar plate method, pointing to the potential applicability in real-world scenarios.

Nanobodies: the Potential Application in Bacterial Treatment and Diagnosis

An infection caused by bacteria is one of the main factors that poses a threat to human health. A recent report from the World Health Organization (WHO) has highlighted that bacteria that cause blood infections have become increasingly drug-resistant. Therefore, it is crucial to research and develop new techniques for detecting and treating these infections. Since their discovery, nanobodies have exhibited numerous outstanding biological properties. They are easy to express, modify, and have high stability, robust permeability and low immunogenicity, all of which indicate their potential as a substitute. Nanobodies have been utilized in a variety of studies on viruses and cancer. This article primarily focuses on nanobodies and introduces their characteristics and application in the diagnosis and treatment of bacterial infections.

A micro-carbon nanotube transistor for ultra-sensitive, label-free, and rapid detection of Staphylococcal enterotoxin C in food

Staphylococcal enterotoxin C (SEC) is an enterotoxin produced by Staphylococcus aureus, which can cause intestinal diseases. Therefore, it is of great significance to develop a sensitive detection method for SEC to ensure food safety and prevent foodborne diseases in humans. A field-effect transistor (FET) based on high-purity carbon nanotubes (CNTs) was used as a transducer, and a nucleic acid aptamer with high affinity was used for recognition to capture the target. The results indicated that the biosensor achieved an ultra-low theoretical detection limit of 1.25 fg/mL in PBS, and its good specificity was verified by detecting target analogs. Three typical food homogenates were used as the solution to be measured to verify that the biosensor had a swift response time (within 5 min after sample addition). An additional study with a more significant basa fish sample response also showed excellent sensitivity (theoretical detection limit of 8.15 fg/mL) and a stable detection ratio. In summary, this CNT-FET biosensor enabled the label-free, ultra-sensitive, and fast detection of SEC in complex samples. The FET biosensors could be further used as a universal biosensor platform for the ultrasensitive detection of multiple biological toxic pollutants, thus considerably stopping the spread of harmful substances.

Nanobody-Based Sandwich Immunoassay for Pathogenic Escherichia coli F17 Strain Detection

Rapid and specific detection of pathogenic bacteria in fecal samples is of critical importance for the diagnosis of neonatal diarrhea in veterinary clinics. Nanobodies are a promising tool for the treatment and diagnosis of infectious diseases due to their unique recognition properties. In this study, we report the design of a nanobody-based magnetofluorescent immunoassay for the sensitive detection of pathogenic Escherichia coli F17-positive strains (E. coli F17). For this, a camel was immunized with purified F17A protein from F17 fimbriae and a nanobody library was constructed by phage display. Two specific anti-F17A nanobodies (Nbs) were selected to design the bioassay. The first one (Nb1) was conjugated to magnetic beads (MBs) to form a complex capable of efficiently capturing the target bacteria. A second horseradish peroxidase (HRP)-conjugated nanobody (Nb4) was used for detection by oxidizing o-phenylenediamine (OPD) to fluorescent 2,3-diaminophenazine (DAP). Our results show that the immunoassay recognizes E. coli F17 with high specificity and sensitivity, with a detection limit of 1.8 CFU/mL in only 90 min. Furthermore, we showed that the immunoassay can be applied to fecal samples without pretreatment and remains stable for at least one month when stored at 4 °C.

Tunable Preparation of SERS-Active Au-Ag Janus@Au NPs for Label-Free Staphylococcal Enterotoxin C Detection

Trace staphylococcal enterotoxin C (SEC) in food poses a serious risk to human health, and it is vital to develop a sensitive and accurate approach for SEC monitoring. Herein, a surface-enhanced Raman scattering (SERS) aptasensor was developed for the quantitative detection of SEC. SERS-active gold-silver Janus@gold nanoparticles (Au-Ag Janus@Au NPs) were prepared and showed tunable solid and hollow nanostructures by simply controlling the pH values of the reaction system. Solid Au-Ag Janus@Au NPs exhibited intrinsic and enhanced SERS activity due to the intense plasmonic coupling effect between Au dots and Au-Ag Janus NPs, which was 2.27-fold and 17.46-fold higher than that of Au-Ag Janus NPs and hollow Au-Ag Janus@Au NPs, respectively. The attachment of multiple Au dots also protected Ag islands from oxidization, which increased the stability of Au-Ag Janus@Au NPs. Solid Au-Ag Janus@Au NPs served as a label-free, strong, and stable SERS detection probe and achieved sensitive and reliable detection of SEC. The limit of detection was as low as 0.55 pg/mL. This study will expand the application prospects of label-free SERS detection probes in complex systems for food safety monitoring.

Single Domain Antibody application in bacterial infection diagnosis and neutralization

Increasing antibiotic resistance to bacterial infections causes a serious threat to human health. Efficient detection and treatment strategies are the keys to preventing and reducing bacterial infections. Due to the high affinity and antigen specificity, antibodies have become an important tool for diagnosis and treatment of various human diseases. In addition to conventional antibodies, a unique class of “heavy-chain-only” antibodies (HCAbs) were found in the serum of camelids and sharks. HCAbs binds to the antigen through only one variable domain Referred to as VHH (variable domain of the heavy chain of HCAbs). The recombinant format of the VHH is also called single domain antibody (sdAb) or nanobody (Nb). Sharks might also have an ancestor HCAb from where SdAbs or V-NAR might be engineered. Compared with traditional Abs, Nbs have several outstanding properties such as small size, high stability, strong antigen-binding affinity, high solubility and low immunogenicity. Furthermore, they are expressed at low cost in microorganisms and amenable to engineering. These superior properties make Nbs a highly desired alternative to conventional antibodies, which are extensively employed in structural biology, unravelling biochemical mechanisms, molecular imaging, diagnosis and treatment of diseases. In this review, we summarized recent progress of nanobody-based approaches in diagnosis and neutralization of bacterial infection and further discussed the challenges of Nbs in these fields.

VHH Structural Modelling Approaches: A Critical Review

VHH, i.e., VH domains of camelid single-chain antibodies, are very promising therapeutic agents due to their significant physicochemical advantages compared to classical mammalian antibodies. The number of experimentally solved VHH structures has significantly improved recently, which is of great help, because it offers the ability to directly work on 3D structures to humanise or improve them. Unfortunately, most VHHs do not have 3D structures. Thus, it is essential to find alternative ways to get structural information. The methods of structure prediction from the primary amino acid sequence appear essential to bypass this limitation. This review presents the most extensive overview of structure prediction methods applied for the 3D modelling of a given VHH sequence (a total of 21). Besides the historical overview, it aims at showing how model software programs have been shaping the structural predictions of VHHs. A brief explanation of each methodology is supplied, and pertinent examples of their usage are provided. Finally, we present a structure prediction case study of a recently solved VHH structure. According to some recent studies and the present analysis, AlphaFold 2 and NanoNet appear to be the best tools to predict a structural model of VHH from its sequence.