We pioneered the use of DC electrophoretic force and electrical resistance measurement between two microwires in a microchannel to respectively extract and detect 1–10 μm polystyrene microplastics in water at 5–100 ppm concentration range.
Considering the increasing concern about the pervasiveness of small microplastics (<20 μm), technologies should invest on detection of particles in these size ranges. Finding the sources of pollution and stopping the spread of microplastics into the environment also need moving toward the development of portable sensors for on-site detection of microplastics.
Here, we proposed a simple low-cost microfluidic device to simultaneously extract and detect microplastics using electrophoretic force and electrical resistance measurement between two microwires in a straight microchannel.
Zabihihesari et al. 2023
Ex situ microplastic detection methods like visual recognition and optical spectroscopy are expensive, time-consuming, and labor-intensive, highlighting the need for on-site rapid detection and quantification technologies. While micro-electro-fluidic devices have been introduced, they require advanced microfabrication and expensive signal processing instruments, while being prone to blockage with larger microplastics, limiting their point-of-need applications.
We developed a simple wide PDMS channel equipped with two copper microwire electrodes, orthogonal to the flow direction and connected to a DC sourcemeter, for electrical resistance-based sensing of 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 will be tested for other types of microplastics in real samples and can be integrated into a handheld device for low cost and on-site microplastic detection.
Microplastic sample preparation before testing with the microfluidic sensor [Zabihihesari et al., 2023].
The proposed microfluidic method for DC electrical microplastic extraction and detection. (A) The experimental setup consisting of the microfluidic sensor, a syringe pump, a DC sourcemeter, and a computer. (B) Close up schematic of the dashed rectangular region of interest in (A) demonstrating microplastics accumulation around the anode during an electrical current sweep [Zabihihesari et al., 2023].
The sensing region of the proposed microfluidic sensor (A) under bright field microscopy for the blank solution and (B), (C) under fluorescent microscopy for 1 μm polystyrene suspension with a concentration of 25 ppm. The accumulation of microplastics around the anode 5 minutes after applying current is shown for the case when flow direction was (B) from the cathode to the anode and (C) vice versa. The flow rate in these experiments was 0.2 mL/min [Zabihihesari et al, 2023].
Normalized resistance drop of 1 μm, 5 μm and 10 μm polystyrene microplastic suspensions at (A) 5 ppm, (B) 25 ppm, and (C) 100 ppm concentrations a flow rate of 0.2 mL/min. Error bars are SD. *: p < 0.05, **: p < 0.01, ***: p < 0.001, ****: p < 0.0001. N = 10 in three independent trials.
Micro and Nanotechnology in Medicine (MNM) conference, the IEEE Engineering in Medicine & Biology Society (EMBS), December 5-9, 2022, Disney Aulani, Hawaii, US, 2022
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