Surface acoustic wave enabled pipette on a chip

Abstract

Mono-disperse droplet formation in microfluidic devices allows the rapid production of thousands of identical droplets and has enabled a wide range of chemical and biological studies through repeat tests performed at pico-to-nanoliter volume samples. However, it is exactly this efficiency of production which has hindered the ability to carefully control the location and quantity of the distribution of various samples on a chip - the key requirement for replicating micro well plate based high throughput screening in vastly reduced volumetric scales. To address this need, here, we present a programmable microfluidic chip capable of pipetting samples from mobile droplets with high accuracy using a non-contact approach. Pipette on a chip (PoaCH) system selectively ejects (pipettes) part of a droplet into a customizable reaction chamber using surface acoustic waves (SAWs). Droplet pipetting is shown to range from as low as 150 pL up to 850 pL with precision down to tens of picoliters. PoaCH offers ease of integration with existing lab on a chip systems as well as a robust and contamination-free droplet manipulation technique in closed microchannels enabling potential implementation in screening and other studies.

A review: controlling the propagation of surface acoustic waves via waveguides for potential use in acoustofluidics

“…The above contributions have allowed FIDTs to be widely employed in acoustofluidic applications where their high intensity and greater beamwidth compression ratio can be utilized. Droplet translation and merging (Jung et al, 2016;Sesen et al, 2017;Sesen et al, 2014), particle concentration and mixing (Collins et al, 2016a;Collins et al, 2017), and cell sorting (Ren et al, 2015;Collins et al, 2016b) have all benefited from the use of FIDTs due to their ability to maximize the proportion of acoustic energy that results in efficient acoustic force gradients and acoustic streaming. As one advanced design of IDTs, rather than propagating forward with a fixed width along the LN substrate, FIDTs successfully manipulate SAWs to some extent, so that they converge into one narrow region or even a small spot.…”

Droplet control technologies for microfluidic high throughput screening (μHTS)

“…2(a)). Sesen et al 104 demonstrated the formation of desired chemical compositions using pipette on a chip platform which makes use of surface acoustic waves to pipette droplets selectively into a side channel (Fig. 2(b)).…”

“…In complex screening studies involving many reagents, the ability to actively control and induce splitting is often desired. At the expense of added complexity, droplet splitting can be achieved by utilising surface acoustic waves (SAWs) offering advanced control over this powerful method 104,172,202 . In one example, SAWs are directed at the oil/water interface whilst approaching a Y-junction ( Fig.…”

“…Depending on the power of the applied TSAWs, the extent of splitting can be controlled 172 . Another design makes use of a by-pass loop integrated to the main microfluidic channel; droplets passing this junction does not split in the absence of SAWs 104 . Once the SAWs are generated, they propel the continuous medium in the upper section of the by-pass loop which leads to a strong suction effect at the by-pass entrance junction when a droplet is passing through.…”

Fast selective trapping and release of picoliter droplets in a 3D microfluidic PDMS multi-trap system with bubbles

“…A system has been shown that is able to trap and release single cancer cells and particles with a hydrodynamic and pressure driven actuation system (one valve per trap), yet with a rather slow performance (e.g. several seconds for loading) 35 Very recently, two devices, using surface acoustic waves, have also been demonstrated, yet they similarly suffer from a slow performance and low droplet rate 36,37 …”