Simple Microfluidic Device for Simultaneous Extraction and Detection of Microplastics in Water Using Dc Electrical Signal

Abstract

In this paper, we used DC electrophoretic force and electrical resistance measurement between two microwires in a microchannel to respectively extract and detect 1-10 µm microplastics in water at 5-100 ppm concentration range. Microplastic pollution of water bodies has highlighted the need for on-site rapid detection and quantification technologies. Ex-situ microplastic detection methods like visual recognition and optical spectroscopy are expensive, time-consuming, and labor-intensive. Recently, micro-electro-fluidic devices have been introduced for microplastic detection based on monitoring the temporary changes in current caused by translocation of single particles through a sensing gate, a narrow constriction, or a thin insolating layer between electrodes. These sensors require advanced microfabrication and expensive signal processing instruments while being prone to blockage when large microplastics and their aggreges are present; thereby limiting their applications for point-of-need detection of microplastics. We developed a simple wide PDMS channel with one inlet, one outlet, and two copper microwire electrodes connected to a DC sourcemeter for sensing polystyrene microplastics in water. Electrical resistance between the two microwires was associated with microplastics’ size and concentration, following their electrophoretic accumulation around the positive electrode.  A positive correlation was found between microplastic concentration and reduction in the normalized resistance. Reducing the flow rate strengthened the extraction and detection of larger microplastics. In the future, the sensor parameters (e.g., sensitivity, limit of detection, limit of quantification, and dynamic range) will be determined for different sizes of microplastics. Moreover, the sensor will be integrated into a handheld device for low cost and on-site microplastic detection.

Keywords: Microplastics, Microfluidics, Extraction, Detection, Concentration, Size