Multimode detection of β -glycosidase and pathogenic bacteria via cation exchange assisted signal amplification

A rapid strategy for the β -glycosidase ( β -Gal) and Escherichia coli ( E. coli ) sensing is presented, which is based on selective recognition reactions of QDs using visualization/fluorescence (FL)/atomic fluorescence spectrometry (AFS)/inductively coupled plasma mass spectrometry (ICP-MS) multimode assay. CdTe QDs can selectively recognize Ag + and Ag NPs with a cation exchange reaction (CER) where Ag + triggers the release of Cd 2+ and quenches the fluorescence signal of QDs. Taking advantage of the fact that β -Gal can hydrolyze 4-Aminophenyl β -D-galactopyranoside (PAPG) to produce p-aminophenol (PAP), which has the ability to reduce Ag + to form Ag NPs. The β -Gal can be easily detected by visualization or FL in a turn-on manner. Furthermore, combining with the selective separation of Cd 2+ by filter membrane, AFS and ICP-MS with higher sensitivity were used for the determination of the enzyme. Under optimized conditions, the system limits of detections (LODs) were 0.01 U/L, 0.03 mU/L, and 0.02 mU/L using FL, AFS, and ICP-MS as the detector, respectively. The relative standard deviations (RSDs, n = 7) for 0.1 U/L β -Gal were 2.2, 2.0, and 1.3% using FL/AFS/ICP-MS as the detector, respectively. And 0.1 U/L of β -Gal can be discriminated from the blank solution with the naked eye. In addition, given that the β -Gal can serve as an indicator of E. coli , we have successfully applied this strategy for the detection of E. coli with a LOD of 25 CFU/mL. Application of the method was demonstrated by analyzing human urine samples and milk samples for ultra-trace detection of E. coli . Graphical abstract The CVG-AFS/ICP-MS/visual/FL multimode β-Gal and E.coli detection via CER.