High-resolution colorimetric detection of lipase activity based on enzyme-controlled reshaping of gold nanorods

We developed a novel enzyme-controlling colorimetric assay to measure lipase activity. The method relied on enzymatic reaction-assisted gold deposition on gold nanorods (AuNRs) to generate a significant color change, which was strongly dependent on lipase activity. The H₂O₂ produced by autoxidation of the ethylene oxide subunits in Tween 80 reduced AuCl₄^- ions to Au atoms, which were coated onto of the surface of the AuNRs. In addition, lipase catalyzed the hydrolysis of the carboxyl ester bond in Tween 80, which controlled the rate of reshaping of AuNRs and tailored the localized surface plasmon resonance of the AuNRs. A linear response ranging from 0 to 4.5 mg mL^-1 and a detection limit of 0.017 mg mL^-1 for lipase were obtained. The methodology provided a sensitive, convenient, and rapid assay to monitor enzyme activities by judging different colors using both naked-eye detection and colorimetric instruments.