Facile colorimetric assay of alkaline phosphatase activity using polydiacetylene liposomes with calcium ions and pyrophosphate

Abstract The detection of alkaline phosphatase (ALP) activity has received great attention since its activity in serum is highly associate with various human diseases. Herein, we describe a simple yet effective colorimetric assay for ALP activity based on polydiacetylene (PDA) and competitive binding of pyrophosphate (PPi) with calcium ions (Ca 2+ ). PDA liposomes prepared from 10,12-pentacosadiynoic acid (PCDA) display the distinct blue-to-red color transition towards Ca 2+ , which can be effectively blocked by PPi due to the ultra-strong binding ability of Ca 2+ with PPi. Since PPi can be specifically hydrolyzed into orthophosphate (Pi) by ALP, the negative effect of PPi could be removed when ALP is introduced into the system, thereby producing a colorimetric signal relying on ALP activity. Based on this strategy, ALP was sensitively and selectively detected with a limit of detection of 5.4 U/L. Besides, the proposed sensing method was successfully applied to evaluate the inhibitor efficiency. Detection of ALP in real human serum samples could also be achieved by this system with acceptable accuracy. As the proposed PDA liposome sensor is simple and straightforward, this strategy holds great potential as a promising alternative for ALP-based clinic diagnosis or biological research.