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

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 . Fe 3 O 4 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 Fe 3 O 4 NPs surface, resulting in the suppression of Fe 3 O 4 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 Fe 3 O 4 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.