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Upconversional Nanoprobe with Highly Efficient Energy Transfer for Ultrasensitive Detection of Alkaline Phosphatase.

Sensitive detection of alkaline phosphatase activity in human serum is important for diagnosis of various diseases. In this work, a novel sandwich structured upconversion nanoparticle, NaYF4:Yb/Er@NaErF4@NaYF4, is fabricated to construct upcon-versional nanoprobe for ultrasensitive detection of phosphate and alkaline phosphatase activity. The inner shell of NaErF4 bridges the emitters in the core with the external luminescence quenchers to greatly improve the energy transfer efficiency. The quencher herein is a coordination complex formed between sulfosalicylic acid and ferric ions. Owing to the higher affinity for phosphate, ferric ions dissociate from the complex and potently combine with phosphate ions, thus interrupting the energy transfer process and recovering the luminescence. This upconversional nanoprobe shows rapid and sensitive detection of phosphate with a limit of detection of 2.5 nM. Since alkaline phosphatase catalyzes the hydrolysis of p-nitrophenyl phosphate to form p-nitrophenol and inorganic phos-phate ions, the nanoprobe is further utilized to achieve sensitive detection of alkaline phosphatase with a limit of detection of 0.5 μU/mL. This novel strategy offers a new opportunity for develop-ing sensitive upconversional nanoprobes and many other energy-transfer-based applications.