High sensitivity detection of: Escherichia coli based on the measurement of β-galactosidase activity by microchip capillary electrophoresis combined with field-amplified sample injection

A sensitive strategy developed for the detection of Escherichia coli (E. coli) by microchip capillary electrophoresis (MCE) combined with laser-induced fluorescence (LIF) is described in this paper. This strategy is based on the measurement of the activity of β-galactosidase (β-gal), an enzyme that is often used as a marker for coliforms. The enzyme activity is detected by the measurement of 4-aminophenol, which is produced upon hydrolysis of the substrate 4-aminophenyl-β-d-galactopyranoside (PAPG) by β-gal. The quantity of 4-aminophenol detected by MCE-LIF was proportional to the concentration of E. coli in the samples. To obtain higher sensitivity of detection, field-amplified sample injection (FASI) was employed in MCE. Under the optimal conditions, the fluorescence responses of 4-aminophenol obtained were directly proportional to the concentrations of E. coli ranging from 20 to 500 CFU mL^-1 with a detection limit of 10 CFU mL^-1. The results confirmed that MCE in combination with LIF is a promising approach for the detection of E. coli with high sensitivity.