AC/DC: Portable diagnostics face the music

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Science Translational Medicine  27 Jul 2016:
Vol. 8, Issue 349, pp. 349ec118
DOI: 10.1126/scitranslmed.aah4504

The unique cancer diagnostic challenges within resource-limited regions have catalyzed the creation of practical yet robust point-of-care (POC) platforms. Using microfluidics for these POC devices is attractive because flow is imperative for precise manipulation of reagents, solutions, or cells of interest. Such systems are often furnished with miniaturized valves and pumps that are prone to failure, so Phillips et al. focused instead on audible-frequency tones to generate controlled flow rates for fluid manipulation within microfluidic channels.

Fluidic systems are like electrical circuits, with fluid molecules and volumetric flow rate being analogous to electrical charge and current, respectively. The electrical potential that gives rise to current is the pressure difference across the channel. Most fluidic systems are driven by constant pressure from external pumps, regarded as DC (direct current) mode. Yet, elementary circuit design depicts AC (alternating current) mode as a means for providing more diverse, frequency-dependent circuits, such as resonators and high- and low-pass filters. The authors exploited these principles to build fluidic networks through combinations of straight channels (representing resistance), flexible diaphragms (capacitors), and audio generators (current source). The researchers created multichannel pump networks controlled by audio tones from a smartphone and demonstrated that different colored fluids representing unique resonant frequencies could be pumped from their inlet reservoirs when their channels’ corresponding audio tones were played.

Although their current AC model only applies to simple channel designs, the ability to generate and control flow rate using portable audio devices is highly promising for POC devices. Impressively, these AC fluidic networks can be custom-designed and frequency-controlled to drive flow through any channel arrangement. The authors only tested saline here and would need to investigate the movement of more complex biofluids, such as blood or urine, if setting sights on POC analyses. The multilayer fabrication and alignment steps they report could also be simplified for real field application and scalability. Modern smartphones are clearly poised to serve as integral hubs of the future, streaming not only your favorite rock songs, but also powering microfluidic sensors and communicating outputs remotely.

R. H. Phillips et al., Flow control using audio tones in resonant microfluidic networks: Towards cell-phone controlled lab-on-a-chip devices. Lab Chip 10.1039/C6LC00738D (2016). [Abstract]

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