Nanobody-Based Biochemical Sensors for Point-of-Care Detection of Aflatoxin B1 in Nigerian Food Commodities: Development and Validation

Rapid, sensitive, and cost-effective detection of aflatoxin B1 contamination in food commodities at the point of collection or sale is a critical food safety need in Nigeria, where aflatoxin exposure contributes to hepatocellular carcinoma risk and stunted child growth. This dissertation develops and validates nanobody-based biochemical sensors for aflatoxin B1 detection applicable to Nigerian food commodity testing in field settings. Single-domain antibody fragments (nanobodies) specific for aflatoxin B1 were selected by phage display biopanning from a dromedary camel immune library immunized with aflatoxin B1-protein conjugate. Selected nanobodies were characterised by surface plasmon resonance binding kinetics, epitope mapping by competitive ELISA, thermal stability assessment, and cross-reactivity profiling against structurally related aflatoxin analogues. The highest-affinity nanobody (KD 0.8 nM) was engineered into three sensor formats: a competitive lateral flow immunoassay, an electrochemical impedimetric biosensor using nanobody-modified gold-thiol electrode surfaces, and a surface-enhanced Raman scattering nanosensor using nanobody-conjugated gold nanoparticles. All three sensor formats were analytically validated against certified reference materials and a spiked food matrix panel including groundnut, maize, and sorghum representative of major Nigerian commodity types. The lateral flow assay achieved a visual detection limit of 1 microgram per kilogram with eighty-three percent agreement with LC-MS/MS reference analysis. The electrochemical biosensor achieved a detection limit of 0.2 microgram per kilogram with quantitative linear range up to 50 microgram per kilogram in a thirty-minute total assay time. Field validation at two Kano State groundnut markets demonstrated practical utility and operator acceptance. Keywords: nanobody, aflatoxin B1 detection, biosensor, food safety, Nigeria.