Development of luminescent nanoswitch for sensing of alkaline phosphatase in human serum based onAl3+-PPi interaction and Cu NCs with AIE properties

As an important biomarker, alkaline phosphatase (ALP) is one of the most commonly assayed enzymes in clinical practice. Here a novel turn-on fluorescent nanoswitch for ALP assay was suggested. The nanoswitch was easily constructed via two high-affinity ligands between GSH and Al³⁺ and PPi and Al³⁺ based on the difference in the affinity. The primary fluorescence of as-prepared GSH capped Cu nanoclusters (NCs) turned on first upon the Al³⁺ addition due to the Al³⁺ induced aggregation induced emission (AIE) enhancement based on the high affinity of GSH and Al³⁺. The presence of PPi then made Al³⁺ desorb from the surface of GSH capped Cu NCs due to the higher affinity of PPi and Al³⁺. As a result, the fluorescence of the Cu NCs was quenched. ALP could hydrolyze PPi into phosphate, destroying the PPi-Al³⁺ complex and releasing Al³⁺. Thus, the Al³⁺ binds to GSH again and the fluorescence was restored. The nanoswitch was demonstrated to be sensitive and selective for ALP assay and was successfully used for the ALP assay in the human serum.