How do you isolate bacteria from small biological samples? A new microfluidic device from scientists in Sweden can do just that.

A team headed by Zhigang Wu, of Uppsala University, has demonstrated a lab-on-a-chip system that can separate bacteria from human red blood cells, whilst keeping both sets of cells alive. Wu heralds the device as a 'simple, cost competitive and robust method' for clinical diagnostics, where it could be used to remove bacteria from a blood sample for quick identification.

The new device exploits the way fluids flow in small spaces to induce cells to separate from the flow of the liquid. The cells' deflection can be tuned to direct particles of a certain size to specific collection chambers. Whilst current methods for cell sorting can be slow and require large volumes to be used, Wu's system dramatically reduces the size of the sample needed. This allows the team to isolate bacteria directly without first needing to culture the samples, a time consuming process.

Wu says that 'the expected "killer applications" [of lab-on-a-chip devices] have not appeared until recently. Part of the reason for the delay is that many chip approaches only miniaturise their macro components instead of exploiting the advantages of microfluidics itself. By contrast,' he continues, 'the approach that we took was to exploit the combined merits of microtechnologies and microfluidics to achieve something that is difficult to achieve using conventional instruments.' 

Daniel Irimia, an expert in microfluidic analytic techniques at Harvard Medical School, Boston, US, describes the work as 'very creative'. He explains that by integrating two particle focusing strategies, the team has been able to produce a 'system that is quite efficient in separating bacteria from a diluted blood cell suspension.'

As well as its applications in diagnostics, the researchers suggest that the system might find use in -omics research. In this field samples are often large in number but small in size, and using conventional methods for cell sorting and screening can make the process prohibitively long. However, it's the clinical prospects that excite Irimia the most: 'The potential clinical applications in the diagnosis of sepsis and infections are very exciting and well worth the future efforts needed in translating this proof-of-principle into a robust system to be used in a hospital environment,' he says.

Laura Howes

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