The role of channel height and actuation method on particle manipulation in surface acoustic wave (SAW)-driven microfluidic devices

Abstract Surface acoustic wave (SAW) micromanipulation offers modularity, easy integration into microfluidic devices and a high degree of flexibility. A major challenge for acoustic manipulation, however, is the existence of a lower limit on the minimum particle size that can be manipulated. As particle size reduces, the drag force resulting from acoustic streaming dominates over acoustic radiation forces; reducing this threshold is key to manipulating smaller specimens. To address this, we investigate a novel excitation configuration based on diffractive-acoustic SAW (DASAW) actuation and demonstrate a reduction in the critical minimum particle size which can be manipulated. DASAW exploits the inherent diffractive effects arising from a limited transducer area in a microchannel, requiring only a travelling SAW (TSAW) to generate time-averaged pressure gradients. We show that these acoustic fields focus particles at the channel walls, and further compare this excitation mode with more typical standing SAW (SSAW) actuation. Compared to SSAW, DASAW reduces acoustic streaming effects whilst generating a comparable pressure field. The result of these factors is a critical particle size with DASAW (1 \upmu μ m) that is significantly smaller than that for SSAW actuation (1.85 \upmu μ m), for polystyrene particles and a given $$\lambda _{\text {SAW}}$$ λ SAW = 200 \upmu μ m. We further find that streaming magnitude can be tuned in a DASAW system by changing the channel height, noting optimum channel heights for particle collection as a function of the fluid wavelength at which streaming velocities are minimised in both DASAW and SSAW devices

On-demand sample injection: combining acoustic actuation with a tear-drop shaped nozzle to generate droplets with precise spatial and temporal control

An on-demand droplet injection method for controlled delivery of nanolitre-volume liquid samples to scientific instruments for subsequent analysis is presented.</p

Surface acoustic wave enabled pipette on a chip

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

Improved Photocatalytic and Bacterial Growth Inhibition Properties Realized for PbS/SnO2-rGO Nanocomposite

PbS/SnO2 (PS) and rGO-PbS/SnO2 (rPS) nanocomposites (NCs) were synthesized through one-pot green synthesis and chemical precipitation methods. In this paper, a comparison of the synthesized composites' photodegradation and bacterial growth inhibition properties has been conducted. For both composites, XRD analyses show the presence of tetragonal-structured SnO2 and cubic-structured PbS peaks. rGO blending increases PS crystallite size from 29 nm to 34 nm. rPS NC shows uniformly packed grains with well-defined boundaries. Absorption peaks of PS redshifts with rGO inclusion. The decreased band gap for rPS might be due to the synergistic effect of sulfur/oxygen vacancies and significant interaction between rGO and PbS/SnO2 NC. The rPS catalyst demonstrated a maximum degradation efficiency of 93% against rhodamine B (RhB) dye. Antibacterial activity of PbS/SnO2 improves with rGO inclusion. PS and rPS NCs are more resistant to gram-positive bacteria than gram-negative bacteria