Fluorometric determination of the activity of alkaline phosphatase based on the competitive binding of gold nanoparticles and pyrophosphate to CePO4:Tb nanorods.

A fluorometric method is described for the determination of the activity of alkaline phosphatase (ALP). It relies on the competition between gold nanoparticles (AuNPs) and pyrophosphate (PPi) for the coordination sites on the surface of CePO4:Tb nanorods. The green fluorescence of the CePO4:Tb is reduced in the presence of AuNPs due to fluorescence resonance energy transfer (FRET), but can be restored on addition of PPi due to the stronger affinity of PPi to the CePO4:Tb. In the presence of ALP, PPi is hydrolyzed to form phosphate which has much weaker affinity for the CePO4:Tb. Hence, the AuNPs will reassemble on the CePO4:Tb, and fluorescence is reduced. Fluorescence drops linearly in the 0.2 to 100 U·L-1 activity range, and the detection limit is 60 mU·L-1 (at S/N = 3). The method does not require any modification of the surface of the CePO4:Tb and is highly sensitive and selective. The inhibition of ALP activity by Na3VO4 was also studied. In our perception, the method may find application in the diagnosis of ALP-related diseases, in screening for inhibitors, and in studies on ALP-related functions in biological systems. Graphical abstract A assay for the detection of alkaline phosphatase is proposed based on the fluorescence resonance energy transfer between CePO4:Tb and AuNPs. It relies on the competitive binding of AuNPs and pyrophosphate (PPi) to CePO4:Tb and the hydrolysis of PPi by ALP.

Simple and highly selective detection of arsenite based on the assembly-induced fluorescence enhancement of DNA quantum dots.

Novel fluorescent DNA quantum dots (QDs) were synthesized by hydrothermal treatment of G-/T-rich ssDNA at relatively low reaction temperature. The obtained DNA QDs demonstrate unique optical properties, maintain the basic structure and biological activities of ssDNA precursors, which makes the DNA QDs able to specifically bind with arsenite, driving the (GT)29 region suffer conformation evolution and form well-ordered assembly rather than random aggregations. We speculate that the strong inter-molecule interaction and efficient stacking of base pairs stiffen the assembly structure, block the nonradiative relaxation channels, populate the radiative decay, and thus making the assembly be highly emissive as a new fluorescence center. The arsenite-induced specific fluorescence enhancement facilitates DNA QDs as light-up probes for arsenite sensing. Under optimal conditions, a linear relationship between the increased fluorescence intensity of DNA QDs and the logarithmic values of arsenite concentration in the range of 1-150ppb with a detection limit of 0.2ppb (3σ) was obtained. The nanosensor shows excellent selectivity for "turn on" arsenite determination and arsenate does not show any interference, facilitating its application in complex real water analysis.