Rapid and robust detection of pathogenic microorganisms is important for quality and safety control in food production, pharmaceutical industries and water treatment and in health.  The plate count method is the common reference method used for enumeration of bacteria using either specific or general agar for bacterial growth to detect culturable bacteria under specific conditions. While the advantage is the low detection limit, it suffers from long assay time (48 hours). Therefore, there is a significant focus on developing and improving methods for detecting and quantifying bacterial cells. Capillary electrophoresis (CE) has been explored as an alternative method for separation and identification of microorganisms due to its robust nature including fast analyses, easily automated and low detection limit.  It is possible to detect a single fluorescently stained cell using laser-induced fluorescence (LIF) – the challenge to do this is from a volume that is useful instead of the nanolitres (nL) that are typically injected into a capillary.

Previously, we reported the use of ITP under FASI conditions to concentrate and detect the cells using LIF. The cells were stained with SYTO 9 in a lower concentration of trailing electrolyte (TE) and using electrokinetic injection to inject and concentrate the cells into a single peak prior to LIF detection. We have successfully demonstrate that this methods are capable to detect cells with limit of detection (LOD) of 135 cells/mL using SYTO 9.¹ This work will describe our recent attempts to lower this further through the use of pressure during the ITP-FASI injection to allow more cells to be injected and stacked before reaching to the detector hence, further lower the detection limit.

(1)           Phung, S. C.; Nai, Y. H.; Powell, S. M.; Macka, M.; Breadmore, M. C. Electrophoresis 2013, 34, 1657–1662.