The visual detection of amoxicillin using a dual-mode probe based on CQDs-doped MnO2 nanospheres

Abstract

Amoxicillin (AMO), a broad penicillin antibiotic, has been widely employed for the treatment of bacterial infections. However, the unreasonable use of amoxicillin may cause a serious threat to human health and its visual determination remains a challenge. Herein, a MnO2@CQDs probe was used for the dual-mode detection of AMO, which was synthetized by CQDs doped in MnO2 nanosphere. In the colorimetric mode, MnO2@CQDs oxidized colorless 3, 3ʹ, 5, 5ʹ-tetramethylbenzidine (TMB) into yellow oxidized TMB (oxTMB). In the presence of AMO, the AMO could deoxidize oxTMB to cause multiple color changes from yellow to colorless. In the fluorescence mode, MnO2@CQDs initially exhibited quenched fluorescence due to the presence of MnO2. Upon the addition of AMO, MnO2 was reduced to Mn2⁺ ions, then CQDs were released and recovered fluorescence at the emission wavelength of 450 nm. The colorimetry detection range was wide from 0.005 to 0.09 μM, and the detection limit was 1.6 nM. With increasing concentration of AMO, the color changed from yellow to colourless which allowed naked eye observation. The fluorescence method was rapid, requiring only 1 min, and exhibited a linear detection range from 0.003 to 0.045 μM, with a detection limit as low as 1 nM. In addition, a paper-based sensing platform was constructed, where fluorescence intensity transitioned from dark to blue with increasing AMO levels. The RGB analysis demonstrated that AMO concentration could be discriminated effectively using a smartphone-assisted detection system. The MnO2@CQDs sensor showed excellent selectivity and specificity for AMO colorimetric and fluorescence detection. Moreover, the probe exhibited good practicability in tap water, milk and serum, with results comparable to those obtained by high-performance liquid chromatography. Overall, the MnO2@CQDs dual-mode probe provides an efficient, convenient and rapid strategy for the visual and quantitative detection of AMO in complex environments.