A promising design of microfluidic electromembrane extraction coupled with sensitive colorimetric detection for colorless compounds based on quantum dots fluorescence.

In the present study, a microfluidic platform was exploited for electromembrane extraction. For device integration as a lab-on-a-chip system, the detection step was carried out by a colorimetric method based on fluorescence quenching of quantum dots. The model analyte was transferred under a pulsed applied electrical field across a polypropylene membrane, impregnated with 1-Octanol, into a final aqueous acceptor phase. The obtained acceptor phase was added into a solution containing CdTe quantum dots. Quenching of the quantum dots was tracked by analyzing the main three color components of red, green, and blue in different concentration levels of the analyte. All effective parameters on the extraction efficiency, fluorescence detection, and synthesis of quantum dots were optimized. Under the optimal conditions, the detection was accomplished by three different detection methods including HPLC-UV, spectrofluorometric detection, as well as colorimetry detection via a smartphone. Calibration curves were linear in the range of 2.0-500 µg L-1 for LC-UV, 30-2500 µg L-1 for fluorescence detection, and 2.5-20 µg mL-1 for image analysis. Inter- and intra-assay relative standard deviations were less than 10.1% in all detection modes.