Microfluidic fractionation of microplastics, bacteria and microalgae with induced-charge electro-osmotic eddies.

Background: Fractionation of microalgal cells has important applications in producing pharmaceuticals and treating diseases. Multiple types of microalgal cells generally coexist in the oceans or lakes and are easily contaminated by microplastics and bacteria. Therefore, it is of paramount significance to develop an effective fractionation approach for microalgal cells for biological applications. Counter-rotating induced-charge electro-osmotic (ICEO) eddies present unique advantages in separating microalgal cells for flexible electrode extension fashion and profile regulation manner. Enthused by these, we proposed a contact-free microfluidic approach for the fractionation of microplastics, bacteria, and microalgae with extensible counter-rotating ICEO eddies.

Results: Firstly, we investigated the flow-field distribution actuated by counter-rotating ICEO eddies, the influence of working parameters on the fluid velocity, and the effect of particle sizes and charges on particle separation. Secondly, depending on the investigation of the movement of microparticles and microalgal cells, we explored synthetic effects of flow rate, voltage, and frequency on the fractionation of microalgal cells from microplastics with an efficiency of about 100 %. Thirdly, this method was used to remove the bacteria for pure Dunaliella salina with a purity of about 95.24 %. Fourthly, this approach was engineered in the fractionation of Diatoms, Chlorella, and Dunaliella salina, and the influence of voltage and frequency on the purity of microalgae was studied. Finally, we proposed a multi-stage separation of microalgal cells with extended counter-rotating ICEO eddies and obtained an efficiency of 91.00 % in the first stage and a purity of 91.55 % and 90.48 % in the second stage.

Significance: This contact-free method holds good potential in the selection of target microalgal cells to address the tricky issues of chronic wound treatment with the advantage of flexible electrode extension fashion and profile regulation manner.