SiO₂/Si interferometers designed for on-site botulinum neurotoxin serotypes B and C quantification and biological...

Botulinum neurotoxins (BoNT), the agent causing botulism, exhibit the highest potency among bacterial toxins and pose a significant threat to both humans and animals. The current in vivo method (mouse lethality assay, MLA) is inappropriate for real-time and pen-side assessment of the occurring outbreak or case. Herein, we describe a reflective-based biosensor capable of detecting the toxin's type and activity state by competitive immunoassay and endopeptidase activity, respectively. Two serotypes (BoNT-B and BoNT-C) were assessed independently by SiO₂/Si interferometers using simulating antigens or specific peptides (i.e., synaptosomal-associated protein and vesicle-associated membrane protein). The reflective responses of both platforms were biochemically amplified using 4-chloro-1-naphthol oxidation into insoluble products. The resulting refractive index variations were observed in real-time using reflective interferometric Fourier transform spectroscopy. The portable bioassay depicted high sensitivity, selectivity, and near real-time rapid assessment (0.14 and 0.47 pg mL^-1 for BoNT-C and BoNT-B, negligible interferences with interfering serotypes, respectively). Additionally, the applicability of the bioassay for monitoring extracted toxins was tested against the in vivo method with satisfactory performance values. Overall, the presented approach can improve field assessment of new botulism incidences by acquiring epidemiological data in near real-time, thus eliminating the need for the MLA approach.