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Microfluidic Device for the Determination of Water Chlorination Levels Combining a Fluorescent meso-Enamine BODIPY Probe and a Micro-hydrocyclone for Gas Bubble Separation.

Chlorination procedures are commonly applied in swimming-pool and waste water treatment, yet also in food, pharmaceutical and paper production. The amount of chlorine in water needs to be strictly controlled, to ensure efficient killing of pathogens but avoiding the induction of negative health effects. Miniaturized microfluidic fluorescence sensors are an appealing approach here when aiming at on-line or at-site measurements. Two meso-enamine-substituted BODIPY dyes were found to exhibit favorable indication properties, their reaction with hypochlorite leading to strong fluorescence enhancement. Real time assays became possible after integration of these fluorescent probes with newly designed 2D and 3D microfluidic chips, incorporating a passive sinusoidal mixer and a micro-hydrocyclone, respectively. A comparison of the two microfluidic systems, including their abilities to prevent accumulation or circulation of micro-bubbles produced by the chemical indication reaction, showed excellent fluidic behavior for the micro-hydrocyclone-based device. After coupling to a miniaturized optical reader for fluorescence detection, the 2D microfluidic system showed a promising detection range of 0.04‒0.5 mg L‒1 while still being prone to bubble-induced fluctuations and suffering from considerably low signal gain. The micro-hydrocyclone-based system was distinctly more robust against gas bubbles, showed a higher signal gain and allowed to halve the limit of detection to 0.02 mg L-1. The use of the 3D system to quantify the chlorine content of swimming pool water samples for sensitive and quantitative chlorine monitoring was demonstrated.