Using obstacle trenches for enhancing microplastic trapping in microwells

The particle trapping efficiency of microwells is influenced by the fluid flow velocity. If the flow velocity is too slow, trapping will take longer. In contrast, if the flow velocity is too fast, the trapping efficiency will decrease. Therefore, deceleration near the microwells is important for increasing trapping efficiency. The aim of this study is to investigate important factors that affect local flow velocity and trapping efficiency. This includes the presence of obstacle trenches, flow rates, particle concentrations, particle sizes, and surface materials. Two models were investigated and compared: one with triangular obstacle trenches placed in front of the microwells and a control model without trenches. Trapping efficiency was evaluated by counting the number of particles trapped within the microwells. The obstacle trenches were designed as equilateral triangles while the microwells were designed as square shape with depths of 300 and 600 micrometers. The channel height was 500 micrometers, and the experimental particles were 10 and 30 micrometers in diameter. Experimental results showed that the model with obstacle trenches achieved approximately twice the trapping efficiency compared to the control. Additionally, both particle concentrations and flow rates showed similar trends, with lower flow rates achieved higher trapping efficiency. However, under high flow rate, the trapping efficiency decreased. This indicates that both factors negatively affect trapping efficiency at high flow rate condition. In contrast, larger particles (30 micrometers) and changing the surface material from resin to PDMS had a more significant impact on trapping efficiency than other factors. After confirming that obstacle trenches increase trapping efficiency, a microfluidic chip was integrated with an impedance-based detection system for identifying microplastics in water. It was found that pure water maintained a constant electrical resistance, whereas the presence of microplastics caused the resistance to increase over time. Ultimately, we anticipate that improving the efficiency of both trapping and detecting microplastics will contribute to better water quality and raise awareness of the dangers of microplastic contamination, representing a crucial step toward long-term improvement in quality of life.