Reproducible bubble-induced acoustic microstreaming for bead disaggregation and immunoassay in microfluidics

Abstract

The bead-based immunoassay requires not only efficient mixing but also good control of bead-surfacearea-to-sample-volume ratio to realise accurate and reproducible detection of low concentration samples. This paper reports the development of a microfluidic platform with the reproducible and efficient bubbleinduced micromixing for bead disaggregation and immunoassay of prostate-specific antigen (PSA). The platform consists of a microfluidic chip with a microchamber and rectangular traps for capturing air bubbles and a home-made controller to generate sound wave using an external piezo transducer. Methods for reproducible bubble formation and bubble size control during mixing are explored. The influence of driving voltage, PDMS thickness and the substrate material on the mixing efficiency is characterised by mixing a fluorescence dye and a buffer solution. The optimised acoustic microstreaming is able to break clusters with hundreds of beads and homogenise individual beads over the microchamber. Immunoassay with efficient micromixing has been applied to PSA immunoassay with greatly reduced detection time. This study provides a practical guide for the design and development of the bubble-induced acoustic micromixers for bead disaggregation and on-chip immunoassays.

Versatile hybrid acoustic micromixer with demonstration of circulating cell-free DNA extraction from sub-ml plasma samples

“…This frequency is mainly a function of geometrical bubble parameters and can be theoretically estimated. 29 However, the resonant frequency can also be experimentally determined by visual observation due to the limited predictability of the models 16 and fabrication tolerances of the 3D printed moulds. Briefly, a frequency sweep is performed using a signal generator, and the microstreaming phenomenon is observed under the digital microscope.…”

“…These mixing times are comparable or better to similar previous static-flow bubble-based micromixers; however, these devices operate in significantly smaller volumes and have the drawback of the glued piezoelectric disc. [16][17][18][19] Moreover, the hybrid micromixer can perform efficient mixing over a wide range of volumes, something unique to our system. As a comparison, diffusion only mixing takes approximately 36 hours to homogenise the species in a 200 μl chamber (Fig.…”

“…This is a clear advantage over previously reported devices where all the micromixers would be activated simultaneously as they share the same substrate. [16][17][18][19]22 Integration of the mixer into 3D printed chips…”

“…Acoustic microstreaming has been shown to be an efficient mechanism to disaggregate and mix microbeads in microfluidic devices. 16 To evaluate the capabilities of our system to perform these operations, we fabricated a microfluidic chip (Fig. S8A †) containing a micromixing chamber of approximately 255 μl.…”

“…Researchers have previously developed a variety of highly efficient bubble-based micromixers, [13][14][15][16][17][18][19][20][21][22][23][24] but most of them are fabricated using (SU-8 mould) soft-lithography, a highly manual and laborious technique that requires specialised equipment and is difficult to mass-manufacture. Furthermore, the total cost of microfluidic chips fabricated using this technique is usually underestimated and can be unaffordable for many research groups.…”