Colorimetric detection of active botulinum neurotoxin using Cu²⁺ mediated gold nanoparticles agglomeration

We report a colorimetric detection of functional botulinum neurotoxin (BoNT) based on its proteolytic activity. Active BoNT can enzymatically cleave SNAptide, a short peptide with 15 amino acids. The cleaved peptides subsequently induced the agglomeration of gold nanoparticles, allowing a colorimetric signal that can be discerned by the naked eye at the low concentration of 1 ng/mL (6.67 pM), and achieve low limit of detection at 0.25 ng/mL (1.67 pM 3 σ/s) by spectral absorbance. This colorimetric detection will provide a simple and promising method for applications at low-resource sites.