Wulff-type boronic acid-functionalized quantum dots for rapid and sensitive detection of Gram-negative bacteria

Abstract

Bacterial infection is a major threat to human health. However, traditional bacteria detection methods need long time and specific conditions. This work reports a fluorescent Gram-negative bacteria probe based on CdSe/CdS/ZnS quantum dots (QDs). The interaction between L-cysteine (Cys) - 4-aminophenylboronic acid (APBA) functionalized QDs (QDs/Cys-APBA) and bacteria outer surfaces lipopolysaccharide induces rapid quenching of the fluorescence of QDs. Escherichia coli and P. Aeruginosa, two typical Gram-negative bacteria, can be detected in 30 min and with a lower limit of detection (LOD) of 58 and 97 CFU/mL, respectively. The probe with the Wulff-type boronic acid structure formed by Cys and APBA is very sensitive to Escherichia coli over a relative wide range of pH from 5.0 to 9.0. It retains high selectivity and sensitivity in the presence of other Gram-positive bacteria such as Staphylococcus aureus and Bacillus subtilis. Its practical potential is shown for estimating the degree of Escherichia coli contamination in cow milk. Meanwhile, bacteria growth is hardly affected by the presence of the QDs/Cys-APBA in the detection process, showing the robustness of the QDs/Cys-APBA as a probe for bacteria detection. This study provides an efficient route for rapid and highly sensitive pathogen diagnosis.