Ultrasensitive and rapid detection of Hg²⁺ in milk based on β-galactosidase driven colloidal motors

In this study, we present a new β-galactosidase-powered Janus colloidal motor for the active and rapid detection of Hg²⁺ in milk. The colloidal motor was fabricated by depositing a thin gold layer on one side of the self-assembled polyelectrolyte capsule, followed by immobilizing β-galactosidase and nitrogen-doped carbon quantum dots asymmetrically on the other side of the polyelectrolyte capsule. β-Galactosidase on the surface of the gold side can decompose the lactose in milk into glucose and galactose, leading to active motion. Furthermore, since nitrogen-doped carbon quantum dots on the colloidal motor's surface can be quenched by Hg²⁺ in milk, such colloidal motors are found to serve as an effective fluorescent sensing platform for the sensitive detection of Hg²⁺ ions. Benefiting from the efficient movement of the colloidal motors, the interaction between the nitrogen-doped carbon quantum dots and the quenched substrate is greatly enhanced, thus improving the detection efficiency and accuracy of Hg²⁺. Under the optimized conditions, the colloidal motors achieved a linear detection range of 0.031–15 μM and the low detection limit of 9.1 nM. The colloidal motors are proving to be an attractive multifunctional sensor platform, providing a valuable means of monitoring Hg²⁺ contamination in dairy products.