Novel activity assay for botulotoxin A1 detection using functionalized chips and matrix-assisted laser desorption/ionization mass spectrometry

Botulinum neurotoxins (BoNTs) are a group of neurotoxins produced by Clostridium bacteria. Their effect on neuro-muscular connections through cleaving proteins of the SNARE complex results in blocking acetylcholine signal transduction. The FDA-approved mouse bioassay, which involves exposing live mice to potentially contaminated food, is the most widely used method. However, this assay is costly, time-consuming, and raises ethical concerns. Therefore, there is a need for alternative assays that can enzymatically measure the activity of BoNTs. We present an approach that combines the EndoPep-MS assay with protein affinity chips fabricated using ion soft-landing technology. Toxic activity is indirectly assessed by monitoring the N- and C-terminal fragments of the substrate peptide. This new method employs a protein array with affinity molecules targeting either the BoNT/A1 or the substrate peptide. Both variants enable <i>in-situ</i> reaction and detection of substrate peptides via MALDI-ToF MS on the protein chip. This method demonstrated successful detection of active BoNT/A1 in both buffer and complex matrices, achieving a detection limit of 0.5 ng/mL. This study reports the <i>in-situ</i> detection of botulotoxin A1 using functionalized MALDI chips. The advantages of the MALDI chip technology include speed, robustness, cost-effectiveness, and possible automatization.