Lateral Flow Immunochromatographic Assay for Competitive Detection of Crustacean Allergen Tropomyosin Using Phage-Displayed Shark Single-Domain Antibody

Nanobody-Induced Aggregation of Gold Nanoparticles: A Mix-and-Read Strategy for the Rapid Detection of Cronobacter sakazakii

Protein-nanoparticle interactions play a crucial role in both biomedical applications and the biosafety assessment of nanomaterials. Here, we found that nanobodies can induce citrate-capped gold nanoparticles (AuNPs) to aggregate into large clusters. Subsequently, we explored the mechanism behind this aggregation and proposed the "gold nucleation mechanism" to explain this phenomenon. Building on this observation, we developed a one-step label-free colorimetric method based on nanobody-induced AuNP aggregation. When nanobodies bind to target bacteria, spatial hindrance occurs, preventing further AuNPs aggregation. This alteration in surface plasmon resonance properties results in visible color changes. As an example, we present a simple and sensitive "mix-and-read" chromogenic immunosensor for Cronobacter sakazakii (C. sakazakii). The experiment can be completed within 20 min, with a visual detection limit of 103 CFU/mL and a quantitative detection limit of 136 CFU/mL. Importantly, our method exhibits no cross-reactivity with other bacterial species. This strategy harnesses the excellent properties of nanobodies and the optical characteristics of AuNPs for direct and rapid detection of foodborne pathogen.

Plasmonic enzyme immunoassay via nanobody-driven controllable aggregation of gold nanoparticles for detection of ochratoxin A in pepper

Ochratoxin A (OTA) in food poses a serious challenge to public health. Herein, using the nanobody-driven controllable aggregation of gold nanoparticles (AuNPs) in a glucose oxidase-tyramine-horseradish peroxidase (GOx-TYR-HRP) system, we propose a direct competitive plasmonic enzyme immunoassay (dc-PEIA) for OTA detection. The OTA-GOx conjugate catalyzes glucose to produce hydrogen peroxide (H2O2), and then HRP catalyzes H2O2 to generate hydroxyl radical which induces the crosslink of TYR. Crosslinked TYR leads to aggregation of AuNPs through strong electrostatic interactions, which is tunable based on the competition of OTA-GOx and free OTA for binding the immobilized nanobody. The optimized dc-PEIA achieves an instrumental limit of detection (LOD) of 0.275 ng/mL and a visual LOD of 1.56 ng/mL. It exhibits good selectivity for OTA and accuracy in the analysis of pepper samples, with the confirmation of high-performance liquid chromatography. Overall, the dc-PEIA is demonstrated as a useful tool for detecting OTA in food.

Single-Domain Antibodies-Novel Tools to Study and Treat Allergies

IgE-mediated allergies represent a major health problem in the modern world. Apart from allergen-specific immunotherapy (AIT), the only disease-modifying treatment, researchers focus on biologics that target different key molecules such as allergens, IgE, or type 2 cytokines to ameliorate allergic symptoms. Single-domain antibodies, or nanobodies, are the newcomers in biotherapeutics, and their huge potential is being investigated in various research fields since their discovery 30 years ago. While they are dominantly applied for theranostics of cancer and treatment of infectious diseases, nanobodies have become increasingly substantial in allergology over the last decade. In this review, we discuss the prerequisites that we consider to be important for generating useful nanobody-based drug candidates for treating allergies. We further summarize the available research data on nanobodies used as allergen monitoring and detection probes and for therapeutic approaches. We reflect on the limitations that have to be addressed during the development process, such as in vivo half-life and immunogenicity. Finally, we speculate about novel application formats for allergy treatment that might be available in the future.

Colorimetric and surface-enhanced Raman scattering dual-mode lateral flow immunosensor using phage-displayed shark nanobody for the detection of crustacean allergen tropomyosin

Tropomyosin (TM) is the primary allergenic protein responsible for crustacean food allergies, and thus sensitive and rapid methods are required for the screening of crustacean TM in food. In this study, using the phage-displayed shark nanobody (PSN) as a multifunctional biomaterial, we developed a colorimetric and surface-enhanced Raman scattering dual-mode lateral flow immunosensor (CM/SERS-LFI) for competitive detection of crustacean TM. The SERS tag AuMBA@AgNPs with the Raman signal molecule 4-mercaptobenzoic acid (4-MBA) was prepared and immobilized on the PSN to construct the immunoprobe AuMBA@Ag-PSN. The probe can identify free TM that competes with TM on the T-line, and the optimized CM/SERS-LFI enables quantitative analysis of TM using the probe with a limit of detection (LOD) of 0.0026 μg/mL (SERS mode) and 0.0057 μg/mL (colorimetric mode), respectively. Additionally, it can implement a qualitative analysis by the naked eye with a visual LOD of 0.01 μg/mL. The CM/SERS-LFI exhibited excellent performance in the tests of selectivity, accuracy, precision, and stability. Moreover, the method's effectiveness in the analysis of real samples was confirmed by a commercial ELISA kit. Therefore, the developed CM/SERS-LFI was demonstrated to be a powerful and reliable tool for the rapid and sensitive detection of crustacean TM in food.

Rapid immunoassay for dual-mode detection of HPV16 and HPV18 DNA based on Au@PdPt nanoparticles

Cervical cancer (CC) remains one of the most severe global health challenges affecting women, primarily due to persistent infection with high-risk human papillomavirus (HPV) subtypes, particularly with HPV16 and HPV 18. Effective detection of these high-risk HPV strains is crucial for CC prevention. Current screening programs for HPV DNA include PCR and in situ hybridization, which are accurate and sensitive. However, these approaches demand a high level of expertise, along with expensive instruments and consumables, thus hindering their widespread use. Therefore, there is a compelling demand to develop an efficient, straightforward, and cost-effective method. Herein, we propose a lateral flow immunoassay (LFIA) method based on Au@PdPt nanoparticles for the simultaneous detection and genotyping of HPV16 and HPV18 within 15 min. This innovative approach allows for qualitative assessment by the naked eye and enables semi-quantitative detection through a smartphone. In this study, under optimal conditions, the qualitative visual limits of detection (vLOD) for HPV16 and HPV18 reached 0.007 nM and 0.01 nM, respectively, which were 32-fold and 20-fold more sensitive than conventional AuNPs-LFIA for HPV16 and HPV18, respectively. Meanwhile, semi-quantitative limits of detection (qLOD) for HPV16 and HPV18 were 0.05 nM and 0.02 nM, respectively. In conclusion, our formulated approach represents a significant step forward in HPV detection and genotyping, with the potential to enhance accessibility and effectiveness in the early diagnosis of CC at the point of care and beyond.