Filter cube

Every experiment was conducted on a microscope (TE2000-U, Nikon, Japan). Individual C. elegans were stably injected into the microchannel through 1 mL syringes (BD Bioscience, USA) administered by an automated syringe pump (neMESYS, Germany). A function generator (AFG3011C, Tektronix, USA) and an amplifier (25A250A, Amplifier Research, USA) were used to drive the IDTs. The resonant frequency of the device was first identified using a network analyzer (Vector Network Analyzer 2180, Array Solutions, USA). Upon identifying the resonant frequency, we then compared the acoustic streaming intensity in the microchannel within a frequency range (±1 MHz) around the resonant frequency at the same amplitude. An optimal driving frequency of 19.32 MHz was chosen because at this frequency the IDTs generated the strongest acoustic streaming in the microchannel. Images and videos were captured by a fast camera (Fastcam SA4, Photron, USA) through Photron FASTCAM Viewer (PFV, Photron, USA). A Nikon filter cube (excitation: 470 nm; emission: 515 nm), a CCD digital camera (CoolSNAP HQ2, Photometrics, USA), and a fiber optic illumination system (Intensilight, Nikon, Japan) were used to record the fluorescent images and videos. All acquired images and videos were analyzed by ImageJ (NIH, USA).