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A colorimetric assay based on polydiacetylenes (PDA) nano-liposomes is reported for facile and sensitive detection of alkaline phosphatase (ALP) activity. The critical basis of this method is that the interaction of pyridoxal phosphate (PLP) with nitrogenous group functionalized PDA nano-liposomes induces distinct blue-to-red color changes of PDA nano-liposomes. In the presence of ALP, as a nature substrate, PLP is enzymatically hydrolyzed to form pyridoxal, which cannot interact with PDA nano-liposomes. As a result, the concentration of PLP is reduced and the color change of PDA nano-liposomes is retarded, which is associated with ALP level. Under optimal conditions, the proposed method showed good linear relationship with ALP activity in the range 10-200 U/L with a limit of detection of 2.8 U/L. The detection process could be vividly observed with the naked eye. Additional attempts by using the method for the evaluation of inhibitor efficiency were also achieved with satisfying results. The method was further challenged with real human serum samples, showing consistent results when compared with a commercial standard assay kit. Such simple and easy-to-use approach may provide a new alternative for clinical and biological detection of ALP., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Graphical abstract Highlights • A colorimetric method based on polydiacetylene liposomes was developed for the detection of alkaline phophatase (ALP). • Ca2+ could induce clear color changes of PDA liposomes from blue to red, while PPi can inhibit this process. • The presence of ALP can remove the inhibition effect of PPi and restore the colorimetric responses. • The detection appoach showed high sensitivity and selectivlty for ALP with the detection limit of 5.4 U/L. • This method could be extended for inhbitor effect evluation and ALP assay in serum samples with acceptable accuracy. 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 (Ca2+). PDA liposomes prepared from 10,12-pentacosadiynoic acid (PCDA) display the distinct blue-to-red color transition towards Ca2+, which can be effectively blocked by PPi due to the ultra-strong binding ability of Ca2+ 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. [ABSTRACT FROM AUTHOR]