A Microfluidic Platform for the Rapid Detection of Microplastics

Abstract

Plastic product is indispensable to human. Due to the limitations of wastewater treatment, collection and management, tremendous amounts of microplastics (MPs) are discharged or generated (by secondary degradation from larger plastic wastes) in the natural environments, leading to an ecological risk and health concern. Moreover, the high consumption of one-off plastic products (e.g., PPE and packaging) for COVID-19 prevention in the past few years has further worsened the problem. For example, it is estimated that there were 1.56 billion face masks, resulting in more than 1370 trillion MPs entering seawater in 2020. Pure plastics are generally non-toxic but usually manufactured with additives or absorb harmful substances from the surrounding. Therefore, MPs can serve as vectors for transferring toxic substances and pathogens to organisms.

Compared to larger MPs, the impact of very small MPs (vsMPs) (i.e., < 10 μm) is increasingly concerning due to their tiny size, making them readily bind to harmful substances and breach tissue barriers. Separation of the vsMPs is essential to assess MP pollution's severity and potential human risks. However, their quantities are consistently underestimated as the lack of effective sorting technologies. Even though some novel technologies have been developed to address the problem, they are still subjected to the need for bulky equipment, trained operations and associated high costs. Moreover, they are usually not applicable to vsMPs.

This doctoral thesis is concerned with developing a portable platform for MPs separation by using spiral inertial microfluidics. This size-based separation technique utilizes the balance of the forces within the spiral microchannel leading to a net force that concentrates target particles on a specific outlet. The technique has gained significant research interest in sorting biological particles because of its relatively high throughput, label-free nature, excellent focusing ability, and ease of integration into other technologies.

As such, this thesis aims to develop the inertial microfluidic technique for MPs separation to address the existing challenges in MPs detection and pollution monitoring. Utilization of the technique, a portable, low-cost and easy-to-use MPs sorting system is developed to make MPs detection more convenient and customize on-site MPs separation. In addition, it is also targeted for sorting vsMPs, which are inadequate to be sorted currently and are consistently underestimated everywhere. The technique combined with the sedimental effect can form a MPs sorting system which can simultaneously separate MPs of a range of sizes (> 100 μm, 20-100 μm, and 2-5 μm) with overall > 85% recovery from a wide range of samples, including seawater, deep-sea sediment and MPs released from plastic containers for food and beverage. Moreover, the technique is portable and easy to integrate with other downstream technologies with a potential to be an on-site MPs detection sensor.

It is hoped that the reported technique would offer a more convenient tool for researchers from different backgrounds to conduct MPs researches and assess the severity of MPs pollution, including those vsMPs to fill the loophole in the current technologies, and would ultimately play a small role in combating global MPs pollution.

Date of Award	28 Aug 2023
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Bee Luan KHOO (Supervisor)