Colorimetric and fluorescent dual-mode detection of Escherichia coli using Fe3O4 nanoparticle coated with fluorescein-labeled aptamer

Abstract

Ensuring the reliable and accurate detection of Escherichia coli (E. coli) is essential for maintaining food safety and safeguarding human health. In this work, a dual-mode sensor that integrates colorimetric and fluorescence detection was developed for the precise identification of E. coli. Fe3O4 nanoparticles (NPs) were coated with a fluorescein-labeled aptamer (FAM-Apt) to enhance their peroxidase-like activity under neutral pH conditions. Simultaneously, this coating also effectively suppressed the fluorescence emitted by FAM. Upon exposure to E. coli, specific binding of the bacteria causes the detachment of FAM-Apt from the Fe3O4 NPs surface, resulting in the suppression of Fe3O4 NPs catalytic activity under neutral pH and the alleviation of the quenching effect on FAM fluorescence. This leads to a simultaneous decrease in the colorimetric signal and an increase in fluorescence signal, facilitating the development of a dual-mode detection method for E. coli with an impressive limit of detection (LOD) of 10 CFU/mL in the colorimetric mode and 6 CFU/mL in the fluorescence mode. This approach highlights the untapped potential of Fe3O4 NPs as a peroxidase mimic in dual-mode sensors, offering a promising strategy for E. coli detection with significant implications for enhancing food safety and public health practices.