Colorimetric detection of botulinum neurotoxin activity using gold nanoparticles

We report a sensitive colorimetric detection of botulinum neurotoxin (BoNT) activity using gold nanoparticles (AuNPs). First, the SNAPtide modified with biotin and cysteine in its two ends, would be cleaved into two short peptides by BoNT activity. The unreacted and cleaved peptides with biotin would be removed by magnetic separation, leaving only cleaved peptides with cysteine end. Next, AuNPs were added to bind with the cleaved peptides via thiol group of cysteine. These AuNPs functionalized with peptides would aggregate and cause a color change by addition of Cu²⁺. By this method, the detection limit of BoNTs reached to 1 ng/ml (6.67 pM), which is so far the most sensitive colorimetric detection of BoNT activity, providing a simple and instrumentation free approach suitable for resource-poor settings.