Smartphone readable colorimetry and ICP-MS dual-mode sensing platform for ultrasensitive and label-free detection of Escherichia coli based on filter-assisted separation

The development and application of portable and user-friendly biosensing technology for rapid detection of pathogenic bacteria are essential for human and environmental care. In this work, based on the phenomenon that the filter membrane can selectively separate MnO2 nanosheets (MnO2 NSs) and Mn2+, a novel label-free sensing platform was developed to detect the Escherichia coli (E. coli) using β-galactosidase (β-Gal) as a marker. MnO2 NSs were utilized as a dual-mode signal molecule of smartphone-based colorimetric analysis and inductively coupled plasma mass spectrometry (ICP-MS). β-Gal can catalyze the 4-Aminophenyl β-D-galactopyranoside (PAPG) to produce p-aminophenol (PAP), which could reduce MnO2 NSs to Mn2+. After selective separation of MnO2 NSs and Mn2+ by the filter, colorimetric detection was achieved with a smartphone by identifying the RGB value of the MnO2 NSs coated membrane, while the Mn2+ in the filtrate was detected by ICP-MS. Under optimal conditions, the limits of detection (LODs) of E. coli by smartphone-based RGB analysis and ICP-MS were 5.6 × 103 CFU mL-1 and 35 CFU mL-1, respectively. This method was successfully used for E. coli assay in meat, vegetables, and fruit samples with the advantages of sensitivity, simplicity, and short incubation time (within 1 h).