Inner filter effect based fluorometric determination of the activity of alkaline phosphatase by using carbon dots codoped with boron and nitrogen

Boron and nitrogen codoped carbon dots functionalized with cyclodextrin (beta-CD-N/B-C-dots) were obtained from beta-cyclodextrin. The material displays strong fluorescence (with excitation/emission peak wavelengths of 400/500 nm) and was characterized by UV-vis, transmission electron microscopy and FTIR. If the substrate p-nitrophenylphosphate is enzymatically cleaved by alkaline phosphatase (ALP), a yellow product is formed whose absorption overlaps the excitation spectrum of the beta-CD-N/B-Cdots. Hence, fluorescence is reduced due to an inner filter effect. In additon, the beta-CD cavity offers a pocket for substrate recognition. The findings were used to design a method for the determination of the activity of ALP. It has a working range that extends from 0.003 to 5.5 U.L-1, with a 0.3 mU.L-1 detection limit. The method is fast, simple, inexpensive, and highly sensitive and selective.