Chemists looking to analyse single cells have combined lab-on-a-chip techniques with lasers to quickly and accurately burst the cells open.

Vasan Venugopalan at the University of California, Irvine, US, and colleagues used pulsed laser microbeams to burst the individual cells in a microfluidic device. The ability to rapidly open (lyse) a cell to examine its content is important when analysing biochemicals such as signalling and messenger molecules, since these can break down within seconds, said Venugopalan. It is also important to achieve high sample throughput.

Venugopalan fine-tuned the lysis process by loading sample cells with fluorescent dyes, and using a rapid camera to capture what happens in the nanoseconds after the cell is hit by the laser pulse. A pulse focused within a few micrometres of the cell produced a rapidly expanding bubble which broke the cell membrane. The growing bubble's excess energy was absorbed as the walls of the microchannel deformed outwards. But as the bubble then collapsed and the walls snapped back into place, the cell contents were re-localised into an area barely any bigger than the original cell, said Venugopalan, which should aid subsequent analysis.

A cell bursts inside a microfluidic channel, deforming the walls; as the walls snap back, the cell contents re-localise

Venugopalan pointed out that using laser irradiation to burst the cell requires no specialised on-chip instruments - unlike previous electrical methods which need on-chip electrodes. 'This can simplify device design, and provides the flexibility to accomplish cell lysis at different locations on the chip.'

Andrew deMello, who develops microfluidic systems at Imperial College London, UK, said the work was very timely, given the current interest in analysing single cells on-chip. 'The process is highly controllable, and allows you to do the analysis of the released cell content there and then,' he said. 'Pulse lasers are now routinely available, out of a catalogue, and theoretically you could integrate the laser with your normal optical detection equipment.'

Venugopalan now plans to start using the device in cell analysis. 'We are pursuing multiple applications, primarily for biochemical analysis of cell lysates, as well as understanding the cellular response to laser-induced perturbations,' he said.

James Mitchell Crow