Alkaline phosphatase (ALP) is a class of enzymes that are widely found in various tissues of the human body. It plays important roles in regulating diverse cellular functions. The aberrant levels of serum ALP are implicated in diseases. The development of sensitive and accurate detection tool for evaluating the level changes of ALP in living organisms will be very helpful in the fields of biochemistry, cytology and clinical medicine. Herein, we develop a near-infrared probe (QcyP) for the specific detection of different ALP levels both in different cell lines and in tumor-bearing mice models. The probe is composed of two moieties: a unique heptamethine cyanine fluorophore and a phosphate monoester. ALP can trigger an off-on fluorescence switch via an enzyme-catalyzed cleavage of the phosphate group. The fluorescence regulation mechanism is based on the rearrangement of the conjugated π-electron system. The probe exhibits high selectivity and good sensitivity towards ALP. The results demonstrate that the probe QcyP not only can be applied to discriminate the levels of ALP in different cell lines, but also can distinguish the ALP level changes between hepatic tumor mice model and normal mice.

碱性磷酸酶（ALP）是一类在人体各种组织中广泛发现的酶。它在调节多种细胞功能中起重要作用。血清ALP异常水平与疾病有关。开发灵敏而准确的检测工具以评估活生物体中ALP的水平变化将在生物化学，细胞学和临床医学领域中非常有帮助。本文中，我们开发了一种近红外探针（QcyP），用于在不同细胞系和荷瘤小鼠模型中特异性检测不同ALP水平。该探针由两个部分组成：独特的七甲胺花青荧光团和磷酸单酯。ALP可以通过酶催化的磷酸酯基团的裂解来触发关闭的荧光开关。荧光调节机制是基于共轭π电子系统的重排。该探针表现出高选择性和对ALP的良好敏感性。结果表明，探针QcyP不仅可以用于区分不同细胞系中的ALP水平，而且可以区分肝肿瘤小鼠模型和正常小鼠之间的ALP水平变化。