ZnAl 2 O 4 :Cr 3+ hollow spheres composed of secondary nanoparticles with single spinel phase were fabricated using carbon templets. Monitoring the emission of 687 nm, two wide excitation bands attributed to the electrons of Cr 3+ transiting from 4 A 2g ( 4 F) → 4 T 1g ( 4 F) and 4 A 2g ( 4 F) → 4 T 2g ( 4 F) were observed. The broad excitation band at about 397 nm was asymmetric and consisted of two peaks, indicating that there was a trigonal distortion existing in the lattices. The intensity of all emitting peaks revealed sharp increasing trend with the sintering temperature increase, and the intensity of emission at 698 nm assigned to inversion defects was more intense than that of emission at 687 nm assigned to octahedral Cr 3+ ions in the undistorted spinel lattice. The samples with higher synthesized temperature revealed longer decay time, and the relative weightage of shorter decay time component decreased with the increase of sintering temperature, indicating that the surface defects decreased.
Jie Zhu,Yang Sun,Meng-Xin Duan,Zheng-Wu Wang,Xin Tan,Zhen Yu,He-Fang Wang
The fast and accurate detection of β-lactamase is a prerequisite of customized treatments and food safety. We present a pretreatment-free dual-excitation three-mode detection of β-lactamase by using ZnAl2O4:Cr3+ etched by ethylenediaminetetraacetic acid disodium (ZAO-EDTA) as a phosphorescent probe and nitrocefin as the signal mediator. The changes in the wavelength overlaps of UV–vis absorbance of nitrocefin upon interactions with β-lactamase and the dual excitation of ZAO-EDTA enable the design of three detection modes: i.e., the enhanced emission when excited at 393 nm, the quenched emission when excited at 533 nm, and the ratio of enhanced excitation of 393 nm and decreased excitation of 533 nm to determine β-lactamase. All three modes have a wide linear range, high sensitivity and selectivity, and fine anti-interference capability. The lowest limit of detection is observed in the ratiometric excitation mode (0.2 U·L–1), and the proposed method can directly detect β-lactamase in bacteria and milk samples without any pretreatments, with the spiked recoveries of 95.3–113% and relative standard deviation < 3.1%. Therefore, the proposed method would be attractive for the detection of β-lactamase in a complex sample, and the ZAO-EDTA probe can be widely used to establish other excitation ratiometric optosensings by changing other signal mediators.
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