As an essential phosphate group hydrolase, alkaline phosphatase (ALP), whose level in serum is correlated with bone disease, liver dysfunction, and cancer, could be used as a biomarker for clinical diagnosis and biomedical studies. Hence, developing a convenient and sensitive method for ALP assay has importance in disease diagnosis, drug treatment, and prognosis assessment. In this work, using a hairpin DNA strand as the substrate, we developed an ultrasensitive and simple fluorescence method for quantitative ALP assay based on the binding diff...