Smartphone readable colorimetry and ICP-MS dual-mode sensing platform for ultrasensitive and label-free detection of...

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).