Trapping stable bubbles in hydrophobic microchannel for continuous ultrasonic microparticle manipulation

The application of bubbles in lab-on-chip devices has attracted considerable attention and is exerting an increasingly significant role in recent years due to its influential functions for fluid and particle manip-ulation. Herein, we demonstrated a simple air bubble trapping method based on the surface tension of hydrophobic chip material and demonstrated particle manipulation utilizing oscillating bubbles. The mi-crofluidic device has a T-shaped junction structure with triangular obstacles, which allows us to transfer air -pocket generated due to non-synchronized liquid filling in the microchannel to stable bubbles attached to channel wall at the desired location. The trapped bubbles can maintain stable state at a flow rate of less than 50 mu L/min. By activating bubbles with the sound wave at a specific frequency, we can achieve particle focusing, trapping, extraction and enrichment in a contact-free, label-free and continuous manner. The proposed bubble trapping method may serve as a reusable, detachable and biocompatible tool for broader bubble-based applications in chemical, biology, and engineering fields, such as drug delivery, cell focusing, as well as isolation of tumor cell. (c) 2021 Elsevier B.V. All rights reserved.