Adenosine triphosphate-triggered lipase colorimetric assay for portable detection of bacterial contamination.

A lipase-based colorimetric assay is presented for on-site detection of bacterial contamination via quantitative determination of adenosine triphosphate (ATP), a universal biomarker for viable bacteria. In this assay, p-nitrophenyl palmitate (pNPP) is encapsulated within zinc-based coordination polymers (ZnCPs), which function as a size-selective barrier to prevent premature substrate hydrolysis. Upon exposure to ATP, the ZnCPs undergo ATP-triggered disassembly, resulting in the controlled release of pNPP. The liberated substrate is subsequently hydrolyzed by lipase, generating a yellow chromogenic product that enables highly sensitive and specific colorimetric detection of ATP. To facilitate practical application and portability, both pNPP@ZnCPs and lipase are co-embedded within an agarose hydrogel matrix, forming a ready-to-use hydrogel test kit. Determination is accomplished via smartphone-based RGB imaging, allowing for rapid and convenient digital quantification of colorimetric changes. The assay exhibits outstanding sensitivity (limit of detection: 0.27 µM for ATP and 2 CFU/mL for Staphylococcus aureus), high selectivity, and robust performance, even in complex sample matrices such as milk and serum. These results underscore the assay’s accuracy, reliability, and significant potential for real-world applications. Designed as a broad-spectrum screening tool, this platform provides a powerful and practical solution for field-based hygiene monitoring and food safety assurance.