3,3′,5,5′-Tetramethylbenzidine assisted construction of a label-free colorimetric and ratiometric fluorescent dual-channel sensor for the detection of levofloxacin

Abstract

A colorimetric and ratiometric fluorescent dual-channel sensor was constructed for levofloxacin (LVFX) detection only using 3,3′,5,5′-tetramethylbenzidine (TMB). LVFX was found to be a light-activatable oxidase mimic, which can generate free radicals and oxidize colorless TMB to blue product (oxTMB) upon irradiation at 365 nm, providing a visible color signal. Interestingly, increasing LVFX concentration causes more TMB to be oxidized, leading to a reduction in the fluorescence intensity of TMB at 410 nm and a rise in the fluorescence intensity of LVFX at 511 nm under excitation at 350 nm. The detection limits of the colorimetric and ratiometric fluorescent sensor for LVFX were 0.26 μM and 0.23 μM, respectively. Moreover, a smartphone-based dual-channel portable device was constructed to integrate the photocatalytic oxidation reaction and the colorimetric and fluorescent detection of LVFX. Successfully detecting LVFX in milk and egg white samples in 5 min suggests the device has great potential in on-site assays.