Acoustofluidic coating of particles and cells

Abstract

On-chip microparticle and cell coating technologies enable a myriad of applications in chemistry, engineering, and medicine. Current microfluidic coating technologies often rely on magnetic labeling and concurrent deflection of particles across laminar streams of chemicals. Herein, we introduce an acoustofluidic approach for microparticle and cell coating by implementing tilted-angle standing surface acoustic waves (taSSAWs) into microchannels with multiple inlets. The primary acoustic radiation force generated by the taSSAW field was exploited in order to migrate the particles across the microchannel through multiple laminar streams, which contained the buffer and coating chemicals. We demonstrate effective coating of polystyrene microparticles and HeLa cells without the need for magnetic labelling. We characterized the coated particles and HeLa cells with fluorescence microscopy and scanning electron microscopy. Our acoustofluidic-based particle and cell coating method is label-free, biocompatible, and simple. It can be useful in the on-chip manufacturing of many functional particles and cells.

Fig. 1

Schematic and working principle of the taSSAW based particle-coating device. (a) 3D illustration of the five-inlet, two-outlet PDMS microchannel and tilted IDTs on lithium niobate (LiNbO₃) substrate. Not to scale. (b) Particles entering the device from the bottom inlet are pushed to the pressure nodes by the acoustic radiation force. While the particles migrating across the microchannel, they are coated with the red stream, washed, coated with the blue stream, and leave the device in the final buffer stream.

Fig. 2

Demonstration of taSSAW-based particle deflection. 20.33 μm polystyrene partciles, the ink solutions, and the buffers are flowing in five layers when the taSSAW is OFF in the (a) active region, and (b) microchannel outlet region. (c) When the taSSAW is ON, the particles are pushed to the pressure nodes and migrate across the two ink solutions by the flow field, and (d) exit the device at the collection outlet.

Fig. 3

Characterization of particle deflection. (a) Stacked images of 20.33 μm particles crossing the microchannel at different acoustic powers. (b) Deflections of 9.51, 15.45, and 20.33 μm polystyrene particles are plotted at varying acoustic power values. Error bars represent standard deviation (n = 10).

Fig. 4

Single-layer coating of 20 μm negatively charged polsytyrene particles and HeLa cells. (a) The particles and the cells are vertically deflected through a fluorescenlty labeled positively charged PAH solution. (b) After removing the background fluorescene intensity of the PAH stream, coated polystyrene particles are seen leaving the stream. (c) The particles and (d) HeLa cells collected from the the collection outlet show conformal coating through fluorescene imaging.

Fig. 5

SEM analysis of (a) the uncoated, (b) PAH coated and (c) PAH/PSS coated polstyrene microparticles. (d) Uncoated polystyrene particles show smooth surfaces. (e) Single-layer (PAH) and (f) double-layer (PAF/PSS) coating shows increasing surface roughness compared to the uncoated particles.

Fig. 6

Zeta potential of uncoated polystyrene (PA), single-layer PAH coated, and double-layer PAH/PSS coated particles. Error bars represent standard deviation of 6 measurements.