Ratiometric detection of copper ions and alkaline phosphatase activity based on semiconducting polymer dots assembled with rhodamine B hydrazide

The rational surface functionalization of semiconducting polymer dots (Pdots) has attracted much attention to extend their applications in fabricating chemo/biosensing platform. In this study, a novel ratiometric fluorescent sensing platform using functionalized Pdots as probes for fluorescence signal transmission has been designed for sensing Cu(II) and activity of alkaline phosphatase (ALP) with high selectivity and enhanced sensitivity. The highly fluorescent Pdots were firstly prepared with Poly[(9,9-dioctylfluoreny1-2,7-diyl)-co-(1,4-benzo-{2,1',3}-thiadiazole)] (PFBT) via nanoprecipitation method, and then assembled with non-fluorescent rhodamine B hydrazide (RB-hy), which shows special binding activity to Cu(II), through adsorption process to obtain functionalized nanohybrids, Pdots@RB-hy. As thus, a FRET donors/acceptors pair, in which PFBT Pdots act as energy donors while RB-hy-Cu(II) complexes act as energy acceptors were constructed. On the basis of the varies in fluorescence intensities of donors/acceptors in the presence of different amounts of Cu(II), a ratiometric method for sensing Cu(II) has been proposed. The proposed ratiometric Cu(II) sensor shows a good linear detection range from 0.05 to 5 mu M with a detection limit of 15 nM. Furthermore, using the Pdots@RB-hyCu(II) system as signal transducer, a ratiometric sensing for alkaline phosphatase (ALP) activity has also been established with pyrophosphate (PPi) as substrates. The constructed ratiometric sensor of ALP activity displays a linear detection range from 0.005 to 15 U L-1 with a detection limit of 0.0018 U L-1. The sensor was further successfully used for ALP activity detection in human serum with satisfactory results.