Pretreatment-Free Dual-Excitation Three-Mode Detection of β-Lactamase in Milk and Bacteria by Cr³⁺-Doped ZnAl₂O₄ Phosphors

Abstract

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 ZnAl 2 O 4 :Cr 3+ 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 βlactamase. 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.