Colorimetric detection of melamine in complex matrices based on cysteamine-modified gold nanoparticles

A sensitive assay for melamine in complex matrices is built using cysteamine-modified gold nanoparticles (AuNPs) and an effective sample pretreatment protocol. Citrate-stabilized AuNPs were modified by cysteamine in order to weaken the electrostatic repulsion force between the gold nanoparticles. Detection sensitivity gained through this modification increased about 100 fold compared with the result using the unmodified AuNPs. Direct colorimetric visualizations of melamine in milk products, eggs and feeds was successfully demonstrated within the linear ranges of 1-200 mg L(-1) and detection limits below 1 mg L(-1). The proposed scheme could be an alternative means for onsite detection of melamine without costly instruments.